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University of York 1 10 July 2015
Electromagnetic properties of nanostructured materials
Ian D Flintoft John F Dawson Iain G Will Linda Dawson
Physical Layer Research Group Department of Electronics University of York
10th July 2015
Contents1 Introduction 3
2 Electromagnetic parameters of materials 3
21 Dielectric properties 4
22 Magnetic properties 5
23 Reflection and transmission at a plane interface 6
24 Reflection and transmission of a TEM wave from a slab 10
25 Reflection and transmission of a TETM wave from a slab in a waveguide 14
26 Contributions to the sample transmission 14
27 Parameter extraction methods 17
271 Nicholson-Ross-Weir parameter extraction 17
272 Thin slab limit 24
273 The effective parameter method 26
274 Sample position and thickness independent methods 28
275 NIST iterative inversion 29
276 MATLAB implementation and experiment simulation 32
3 A coaxial measurement jig 33
31 Design of a coaxial measurement jig 33
32 Coaxial jig test sample manufacture 38
33 Coaxial jig test results 40
4 Nanoparticle film and material fabrication 47
5 Conclusions and Plans for future work 48
51 Material characterisation capability 48
52 Application of nano-particle films 48
53 Proposals and collaboration 49
6 References 49
7 Bibliography 50
Electromagnetic properties of nanostructured materials
University of York 2 10 July 2015
Glossary
CFC Carbon Fibre Composite
CNT Carbon Nano-Tube
DC Direct Current
EMT Effective Medium Theory
GA Genetic Algorithm
NRW Nicholson-Ross-Weir
PTFE Polytetrafluoroethylene
RF Radio Frequency
SE Shielding Effectiveness
SMA Sub-miniature Version A
SNR Signal-to-Noise Ratio
SWCNT Single Walled Carbon Nano-Tube
TE Transverse Electric
TEM Transverse Electromagnetic
TM Transverse Magnetic
VNA Vector Network Analyser
Electromagnetic properties of nanostructured materials
University of York 3 10 July 2015
1 Introduction
This report summarises the progress to date of work funded by the University of York Research
Priming Fund on ldquoElectromagnetic properties of nanostructured materialsrdquo
The inclusion of nanoscale structures within materials has the potential to provide enhanced or
customised electromagnetic properties Applications include shielding of sensitive systems from
electromagnetic radiation (eg as widely used in the electronics and aerospace industries) and the
ability to allow some radio signals to pass whilst preventing others (eg privacy and security
applications) The work has allowed the Physical Layer Research Group to develop its measurement
capability so that the electromagnetic properties of nanostructured materials can be measured and
also to begin working on materials by fabricating a range of nano-particle based films
In Section 2 a review of the electromagnetic properties of materials and the extraction of
electromagnetic parameters from various measurements is discussed The software developed for
parameter extraction is then summarised In Section 3 the design and testing of a coaxial shielding
measurement jig is described In Section 4 the potential nano-structured materials that could be
fabricated to address currently funded research application areas are identified Section 5 provides
some concluding remarks and describes future and ongoing work in this area
2 Electromagnetic parameters of materials
Functionally the electromagnetic performance of materials are often specified in terms of their
transmission and reflection coefficients which define the amplitude and phase of plane
electromagnetic waves that propagate through and are reflected from a sample respectively The
proportion of the incident electromagnetic energy that is absorbed within the material (ie neither
reflected nor transmitted) may also be an important consideration in many application areas These
properties of the material depend on both its internal micro-structure and the overall macroscopic
shape of the material For the purposes of material characterisation a planar sample is often used
since the electromagnetic scattering and transmission from an infinite plane sheet of homogeneous
material is amenable to exact theoretical analysis thereby providing a solid reference for validation
of measurement procedures and numerical simulations
If probed by sufficiently high frequency electromagnetic waves the micro-structure of the material
can be discerned in the characteristics of the scattered waves This applies at different length scales
associated with the physical structure of the material The shortest length scale of interest
corresponds to the nano-scale level in which the atomic structure can be resolved Most
engineering materials have structure at larger length scales associated with their fabrication and
application For example carbon-fibre reinforced composites (CFCs) consist of filaments of carbon
with diameters of the order micro-meters embedded in a dielectric resin The microstructure
therefore has apertures between the fibres with a similar length scale that influences the
electromagnetic properties of the composite even at low frequencies
In many applications the frequencies of interest are far below the length-scale of the microstructure
and a homogenised view of the material can be taken averaging the electromagnetic fields at the
surface of the material to give simpler effective parameters for the material properties This
approach is called Effective Medium Theory (EMT) This is essentially a generalisation of the classical
macroscopic treatment of dielectric and magnetic materials in Maxwellrsquos electromagnetic theory by
Electromagnetic properties of nanostructured materials
University of York 4 10 July 2015
averaging over the atomic level electric and magnetic dipole moments caused by the induced charge
movements in the material when subjected to an external electromagnetic field This leads to the
definition of the classical electric permittivity and magnetic permeability of the material
In this chapter a brief review of the electromagnetic parameters is presented followed by a review
and implementation of the different methodologies that can be employed to extract material
parameters from different measurement system including the coaxial shielding jig described in
Section 3
21 Dielectric properties
Linear isotropic materials can be described by the introducing the electric flux density D that is
related to the electric field E via the complex permittivity ()Ƹߝ
۲() = ()Ƹ()۳ߝ = ε۳() + () = ε۳() + εχොக()۳()
Here ε is the permittivity of free-space P the electric polarisation vector and χොக() the electricsusceptibility The complex permittivity can be decomposed into real and imaginary parts
()Ƹߝ = minusᇱߝ jεᇱᇱ≝ Ƹ()εߝ
where the relative permittivity is
()Ƹߝ = εᇱminus jε
ᇱᇱ= 1 + χොக()ߝ
The real part characterises energy storage in material while the imaginary part characterisesloss due to the bound charge movement The loss tangent is defined ratio of energy lost percycle to energy stored per cycle and given by
tanߜக =εᇱᇱ
εᇱ
allowing the relative permittivity to be written
()Ƹߝ = εᇱ(1 minus j tanߜக)
Some materials have free ionic charges that respond to a DC electric field by producing aconduction current
۸() = ()ୈେ۳ߪ
The overall effective relative permittivity is then
()Ƹߝ = εᇱminus j൬ε
ᇱᇱ+ୈେߪε
൰
In real materials there are often partially bound charges which blur the distinction betweendielectric loss and conduction effects The AC conductivity may be written [Bake2005]
ߪ = minusᇱߪ jߪᇱᇱasymp ୈେߪ minus jߪᇱᇱ
The overall dielectric response is then characterised the a complex relative permittivity
()Ƹߝ = εᇱminus
ᇱᇱߪ
εminus jቆε
ᇱᇱ+ᇱߪ
εቇ
Electromagnetic properties of nanostructured materials
University of York 5 10 July 2015
In order for the material to have a causal time response the complex permittivity must
satisfy the Kramers-Kronig relations
εᇱ() minus ஶߝ = minus
2
ߨන
εߠᇱᇱ(ߠ)minus ε
ᇱᇱ()
minusଶߠ ଶdߠ
ஶ
εᇱᇱ() = minus
2
ߨන
εᇱ(ߠ) minus ε
ᇱ()
minusଶߠ ଶdߠ
ஶ
These can also be written in ldquoonce subtracted formrdquo
εᇱ() minus ε
ᇱ() = minus minus
ߨPVන
εᇱᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
ஶ
εᇱᇱ() minus ε
ᇱᇱ() = minus
ߨPVන
εᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
Various models for the frequency response of a material have been developed- some arelisted in Table 1
Model Dispersion Relation
Drude σ =
ଶ
1
ߛ + j=
ଶ
minusߛ j
ߛଶ + ଶ
Debye()ߝ = ஶߝ +
ߝ∆
1 + j
Lorentz ()ߝ = ஶߝ +ఌଶ
ఌଶ + Γఌω minus ଶ
Cole-Cole[Gabr1996] ()ߝ = ஶߝ +
ߝ∆1 + (j )ଵఈ
+ୈେߪjε
Table 1 Common dispersion models for dielectrics and conductors
22 Magnetic properties
In a completely analogous way the magnetic permeability of a material can be defined by
()Ƹߤ = minusᇱߤ jߤᇱᇱ= +ߤσlowast
j≝ ߤ()Ƹߤ
where σlowast is the magnetic conductance The relative permeability is then
()Ƹߤ = ߤᇱminus jߤ
ᇱᇱ= ߤ +σlowast
jߤ
Electromagnetic properties of nanostructured materials
University of York 6 10 July 2015
Figure 1 Interfacial transmission of TE and TM waves at z-normal boundary
23 Reflection and transmission at a plane interface
The reflection coefficient at an infinite plane interface between two different materials can be
determined from the boundary conditions on the electromagnetic field at the surface Consider a
plane-wave propagating in the z-x plane with wave vector
ܓ ൌ ௫ܠො ௭ܢො
in an isotropic medium with complex permittivity Ƹandߝ permeability Ƹߤ The wave can be
decomposed into transverse electric (TE) and transverse magnetic (TM) components
۳(ܚǢ ) ൌ Ǣܧe୨ܓήܡܚො
۶(ܚǢ ) ൌ Ǣܧ
1
Ƹߤe୨ܓήܚ(െ௭ܠො ௫ܢො)
and
۳ Ǣܚ) ) ൌ Ǣܧ e୨ܓήܚ൬ܠොെ
௫
௭ො൰ܢ
۶ Ǣܚ) ) ൌ Ǣܧ
Ƹߝ
௭e୨ܓήܡܚොǡ
where Ǣܧ and Ǣܧ
are the transverse field amplitudes and the dispersion relation is
௫ଶ ௭
ଶ ൌ ଶߤƸߝƸǤ
If the medium is lossless then the wave-vector is real and can be written
ܓ ൌ መܓ ൌ ොܠߠ) (ොܢߠ
Electromagnetic properties of nanostructured materials
University of York 7 10 July 2015
where is the angle between the z-axis and the wave vector and = ߝߤradic The total amplitudes of
the TE and TM fields are then related to the transverse field amplitudes by
ܧ = ܧ
ܧ = ܧ
cosߠ
The complete transverse fields can be written
۳ = ܧ
e୨௭e୨௫ܡො
۶ = minus
ܧ
ߟ
e୨௭e୨௫ܠො
and
۳ = ܧ
e୨௭e୨௫ܠො
۶ =
ܧ
ߟ
e୨௭e୨௫ܡො
where the transverse wave impedances are defined by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
Writing the total transverse field as
۳ = ܧ +ොܠ ܧ
ܡො
۶ = ܪ minusොܡ ܪ
ܠො
noting the minus sign for the x component of the TE magnetic field the propagation in the medium
is reduced to two uncoupled one-dimensional transmission line problems of the form
(ݖ)ܧ = ܧା(ݖ) + ܧ
(ݖ) = ܧାe୨௭ + ܧ
eା୨௭ = ܧା(ݖ)൫1 + Γ(ݖ)൯
(ݖ)ܪ = ܪା(ݖ) + ܪ
(ݖ) =1
ߟ൫ܧ
ାe୨௭minus ܧeା୨௭൯=
ܧା(ݖ)
ߟ൫1 minus Γ(ݖ)൯
where the e୨௫ phase factor has been suppressed This is illustrated in Figure 1 The propagation
of the forward and backward waves can be described by a propagation matrix
ܧା(ݖଵ)
ܧ(ଵݖ)
൨= e୨(௭మ௭భ) 0
0 e୨(௭మ௭భ)൨ܧା(ݖଶ)
ܧ(ଶݖ)
൨
while the total transverse fields propagate according to a ldquochain matrixrdquo given by
Electromagnetic properties of nanostructured materials
University of York 8 10 July 2015
(ଵݖ)ܧ(ଵݖ)ܪ
൨= cos ௭(ݖଶminus (ଵݖ jߟ sin ௭(ݖଶminus (ଵݖ
jߟଵ sin ௭(ݖଶminus (ଵݖ cos ௭(ݖଶminus (ଵݖ
൨(ଶݖ)ܧ(ଶݖ)ܪ
൨
The electric field reflection coefficient is
Γ(ݖ) =ܧ(ݖ)
ܧା(ݖ)
and propagates according to
Γ(ݖଵ) = Γ(ݖଵ)eଶ୨(௭మ௭భ)
while the wave impedance
(ݖ) =(ݖ)ܧ
(ݖ)ܪ= ߟ
1 + Γ(ݖ)
1 minus Γ(ݖ)
propagates as
(ଵݖ) = ߟ(ଶݖ) cos ௭(ݖଶminus (ଵݖ + jߟ sin ௭(ݖଶminus (ଵݖ
ߟ cos ௭(ݖଶminus (ଵݖ + j(ݖଶ) sin ௭(ݖଶminus (ଵݖ
Note that
Γ(ݖ) =(ݖ) minus ߟ(ݖ) + ߟ
At a plane interface between two semi-infinite media denoted left (L) and right (R) located at z = 0
the transverse electric and magnetic fields must be continuous Matching the phase in the x-
direction at the interface leads to Snellrsquos Law
௫ = ௫
If the left medium is lossless then
௫ = sinߠ= ඥߤƸߝƸ sinߠ = ௫
where is the angle in incidence and hence from the dispersion relationships
൫ ௫൯
ଶ+ ൫ ௭
൯ଶ
= ଶߤƸߝƸ ≝ ൫ ൯ଶ
we find that
௭ = ටଶߤƸߝƸ minus ൫ ௫
൯ଶ
= ඥଶߤƸߝƸ minus ( sinߠ)ଶ
For the left medium ௭ = cosߠ Matching the electric and magnetic fields either side of the
boundary
ܧ = ܧ
ା + ܧ = ܧ
ା + ܧ = ܧ
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
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ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
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or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
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Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
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௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
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ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
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6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
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Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
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Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
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Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 2 10 July 2015
Glossary
CFC Carbon Fibre Composite
CNT Carbon Nano-Tube
DC Direct Current
EMT Effective Medium Theory
GA Genetic Algorithm
NRW Nicholson-Ross-Weir
PTFE Polytetrafluoroethylene
RF Radio Frequency
SE Shielding Effectiveness
SMA Sub-miniature Version A
SNR Signal-to-Noise Ratio
SWCNT Single Walled Carbon Nano-Tube
TE Transverse Electric
TEM Transverse Electromagnetic
TM Transverse Magnetic
VNA Vector Network Analyser
Electromagnetic properties of nanostructured materials
University of York 3 10 July 2015
1 Introduction
This report summarises the progress to date of work funded by the University of York Research
Priming Fund on ldquoElectromagnetic properties of nanostructured materialsrdquo
The inclusion of nanoscale structures within materials has the potential to provide enhanced or
customised electromagnetic properties Applications include shielding of sensitive systems from
electromagnetic radiation (eg as widely used in the electronics and aerospace industries) and the
ability to allow some radio signals to pass whilst preventing others (eg privacy and security
applications) The work has allowed the Physical Layer Research Group to develop its measurement
capability so that the electromagnetic properties of nanostructured materials can be measured and
also to begin working on materials by fabricating a range of nano-particle based films
In Section 2 a review of the electromagnetic properties of materials and the extraction of
electromagnetic parameters from various measurements is discussed The software developed for
parameter extraction is then summarised In Section 3 the design and testing of a coaxial shielding
measurement jig is described In Section 4 the potential nano-structured materials that could be
fabricated to address currently funded research application areas are identified Section 5 provides
some concluding remarks and describes future and ongoing work in this area
2 Electromagnetic parameters of materials
Functionally the electromagnetic performance of materials are often specified in terms of their
transmission and reflection coefficients which define the amplitude and phase of plane
electromagnetic waves that propagate through and are reflected from a sample respectively The
proportion of the incident electromagnetic energy that is absorbed within the material (ie neither
reflected nor transmitted) may also be an important consideration in many application areas These
properties of the material depend on both its internal micro-structure and the overall macroscopic
shape of the material For the purposes of material characterisation a planar sample is often used
since the electromagnetic scattering and transmission from an infinite plane sheet of homogeneous
material is amenable to exact theoretical analysis thereby providing a solid reference for validation
of measurement procedures and numerical simulations
If probed by sufficiently high frequency electromagnetic waves the micro-structure of the material
can be discerned in the characteristics of the scattered waves This applies at different length scales
associated with the physical structure of the material The shortest length scale of interest
corresponds to the nano-scale level in which the atomic structure can be resolved Most
engineering materials have structure at larger length scales associated with their fabrication and
application For example carbon-fibre reinforced composites (CFCs) consist of filaments of carbon
with diameters of the order micro-meters embedded in a dielectric resin The microstructure
therefore has apertures between the fibres with a similar length scale that influences the
electromagnetic properties of the composite even at low frequencies
In many applications the frequencies of interest are far below the length-scale of the microstructure
and a homogenised view of the material can be taken averaging the electromagnetic fields at the
surface of the material to give simpler effective parameters for the material properties This
approach is called Effective Medium Theory (EMT) This is essentially a generalisation of the classical
macroscopic treatment of dielectric and magnetic materials in Maxwellrsquos electromagnetic theory by
Electromagnetic properties of nanostructured materials
University of York 4 10 July 2015
averaging over the atomic level electric and magnetic dipole moments caused by the induced charge
movements in the material when subjected to an external electromagnetic field This leads to the
definition of the classical electric permittivity and magnetic permeability of the material
In this chapter a brief review of the electromagnetic parameters is presented followed by a review
and implementation of the different methodologies that can be employed to extract material
parameters from different measurement system including the coaxial shielding jig described in
Section 3
21 Dielectric properties
Linear isotropic materials can be described by the introducing the electric flux density D that is
related to the electric field E via the complex permittivity ()Ƹߝ
۲() = ()Ƹ()۳ߝ = ε۳() + () = ε۳() + εχොக()۳()
Here ε is the permittivity of free-space P the electric polarisation vector and χොக() the electricsusceptibility The complex permittivity can be decomposed into real and imaginary parts
()Ƹߝ = minusᇱߝ jεᇱᇱ≝ Ƹ()εߝ
where the relative permittivity is
()Ƹߝ = εᇱminus jε
ᇱᇱ= 1 + χොக()ߝ
The real part characterises energy storage in material while the imaginary part characterisesloss due to the bound charge movement The loss tangent is defined ratio of energy lost percycle to energy stored per cycle and given by
tanߜக =εᇱᇱ
εᇱ
allowing the relative permittivity to be written
()Ƹߝ = εᇱ(1 minus j tanߜக)
Some materials have free ionic charges that respond to a DC electric field by producing aconduction current
۸() = ()ୈେ۳ߪ
The overall effective relative permittivity is then
()Ƹߝ = εᇱminus j൬ε
ᇱᇱ+ୈେߪε
൰
In real materials there are often partially bound charges which blur the distinction betweendielectric loss and conduction effects The AC conductivity may be written [Bake2005]
ߪ = minusᇱߪ jߪᇱᇱasymp ୈେߪ minus jߪᇱᇱ
The overall dielectric response is then characterised the a complex relative permittivity
()Ƹߝ = εᇱminus
ᇱᇱߪ
εminus jቆε
ᇱᇱ+ᇱߪ
εቇ
Electromagnetic properties of nanostructured materials
University of York 5 10 July 2015
In order for the material to have a causal time response the complex permittivity must
satisfy the Kramers-Kronig relations
εᇱ() minus ஶߝ = minus
2
ߨන
εߠᇱᇱ(ߠ)minus ε
ᇱᇱ()
minusଶߠ ଶdߠ
ஶ
εᇱᇱ() = minus
2
ߨන
εᇱ(ߠ) minus ε
ᇱ()
minusଶߠ ଶdߠ
ஶ
These can also be written in ldquoonce subtracted formrdquo
εᇱ() minus ε
ᇱ() = minus minus
ߨPVන
εᇱᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
ஶ
εᇱᇱ() minus ε
ᇱᇱ() = minus
ߨPVන
εᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
Various models for the frequency response of a material have been developed- some arelisted in Table 1
Model Dispersion Relation
Drude σ =
ଶ
1
ߛ + j=
ଶ
minusߛ j
ߛଶ + ଶ
Debye()ߝ = ஶߝ +
ߝ∆
1 + j
Lorentz ()ߝ = ஶߝ +ఌଶ
ఌଶ + Γఌω minus ଶ
Cole-Cole[Gabr1996] ()ߝ = ஶߝ +
ߝ∆1 + (j )ଵఈ
+ୈେߪjε
Table 1 Common dispersion models for dielectrics and conductors
22 Magnetic properties
In a completely analogous way the magnetic permeability of a material can be defined by
()Ƹߤ = minusᇱߤ jߤᇱᇱ= +ߤσlowast
j≝ ߤ()Ƹߤ
where σlowast is the magnetic conductance The relative permeability is then
()Ƹߤ = ߤᇱminus jߤ
ᇱᇱ= ߤ +σlowast
jߤ
Electromagnetic properties of nanostructured materials
University of York 6 10 July 2015
Figure 1 Interfacial transmission of TE and TM waves at z-normal boundary
23 Reflection and transmission at a plane interface
The reflection coefficient at an infinite plane interface between two different materials can be
determined from the boundary conditions on the electromagnetic field at the surface Consider a
plane-wave propagating in the z-x plane with wave vector
ܓ ൌ ௫ܠො ௭ܢො
in an isotropic medium with complex permittivity Ƹandߝ permeability Ƹߤ The wave can be
decomposed into transverse electric (TE) and transverse magnetic (TM) components
۳(ܚǢ ) ൌ Ǣܧe୨ܓήܡܚො
۶(ܚǢ ) ൌ Ǣܧ
1
Ƹߤe୨ܓήܚ(െ௭ܠො ௫ܢො)
and
۳ Ǣܚ) ) ൌ Ǣܧ e୨ܓήܚ൬ܠොെ
௫
௭ො൰ܢ
۶ Ǣܚ) ) ൌ Ǣܧ
Ƹߝ
௭e୨ܓήܡܚොǡ
where Ǣܧ and Ǣܧ
are the transverse field amplitudes and the dispersion relation is
௫ଶ ௭
ଶ ൌ ଶߤƸߝƸǤ
If the medium is lossless then the wave-vector is real and can be written
ܓ ൌ መܓ ൌ ොܠߠ) (ොܢߠ
Electromagnetic properties of nanostructured materials
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where is the angle between the z-axis and the wave vector and = ߝߤradic The total amplitudes of
the TE and TM fields are then related to the transverse field amplitudes by
ܧ = ܧ
ܧ = ܧ
cosߠ
The complete transverse fields can be written
۳ = ܧ
e୨௭e୨௫ܡො
۶ = minus
ܧ
ߟ
e୨௭e୨௫ܠො
and
۳ = ܧ
e୨௭e୨௫ܠො
۶ =
ܧ
ߟ
e୨௭e୨௫ܡො
where the transverse wave impedances are defined by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
Writing the total transverse field as
۳ = ܧ +ොܠ ܧ
ܡො
۶ = ܪ minusොܡ ܪ
ܠො
noting the minus sign for the x component of the TE magnetic field the propagation in the medium
is reduced to two uncoupled one-dimensional transmission line problems of the form
(ݖ)ܧ = ܧା(ݖ) + ܧ
(ݖ) = ܧାe୨௭ + ܧ
eା୨௭ = ܧା(ݖ)൫1 + Γ(ݖ)൯
(ݖ)ܪ = ܪା(ݖ) + ܪ
(ݖ) =1
ߟ൫ܧ
ାe୨௭minus ܧeା୨௭൯=
ܧା(ݖ)
ߟ൫1 minus Γ(ݖ)൯
where the e୨௫ phase factor has been suppressed This is illustrated in Figure 1 The propagation
of the forward and backward waves can be described by a propagation matrix
ܧା(ݖଵ)
ܧ(ଵݖ)
൨= e୨(௭మ௭భ) 0
0 e୨(௭మ௭భ)൨ܧା(ݖଶ)
ܧ(ଶݖ)
൨
while the total transverse fields propagate according to a ldquochain matrixrdquo given by
Electromagnetic properties of nanostructured materials
University of York 8 10 July 2015
(ଵݖ)ܧ(ଵݖ)ܪ
൨= cos ௭(ݖଶminus (ଵݖ jߟ sin ௭(ݖଶminus (ଵݖ
jߟଵ sin ௭(ݖଶminus (ଵݖ cos ௭(ݖଶminus (ଵݖ
൨(ଶݖ)ܧ(ଶݖ)ܪ
൨
The electric field reflection coefficient is
Γ(ݖ) =ܧ(ݖ)
ܧା(ݖ)
and propagates according to
Γ(ݖଵ) = Γ(ݖଵ)eଶ୨(௭మ௭భ)
while the wave impedance
(ݖ) =(ݖ)ܧ
(ݖ)ܪ= ߟ
1 + Γ(ݖ)
1 minus Γ(ݖ)
propagates as
(ଵݖ) = ߟ(ଶݖ) cos ௭(ݖଶminus (ଵݖ + jߟ sin ௭(ݖଶminus (ଵݖ
ߟ cos ௭(ݖଶminus (ଵݖ + j(ݖଶ) sin ௭(ݖଶminus (ଵݖ
Note that
Γ(ݖ) =(ݖ) minus ߟ(ݖ) + ߟ
At a plane interface between two semi-infinite media denoted left (L) and right (R) located at z = 0
the transverse electric and magnetic fields must be continuous Matching the phase in the x-
direction at the interface leads to Snellrsquos Law
௫ = ௫
If the left medium is lossless then
௫ = sinߠ= ඥߤƸߝƸ sinߠ = ௫
where is the angle in incidence and hence from the dispersion relationships
൫ ௫൯
ଶ+ ൫ ௭
൯ଶ
= ଶߤƸߝƸ ≝ ൫ ൯ଶ
we find that
௭ = ටଶߤƸߝƸ minus ൫ ௫
൯ଶ
= ඥଶߤƸߝƸ minus ( sinߠ)ଶ
For the left medium ௭ = cosߠ Matching the electric and magnetic fields either side of the
boundary
ܧ = ܧ
ା + ܧ = ܧ
ା + ܧ = ܧ
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
University of York 15 10 July 2015
ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 3 10 July 2015
1 Introduction
This report summarises the progress to date of work funded by the University of York Research
Priming Fund on ldquoElectromagnetic properties of nanostructured materialsrdquo
The inclusion of nanoscale structures within materials has the potential to provide enhanced or
customised electromagnetic properties Applications include shielding of sensitive systems from
electromagnetic radiation (eg as widely used in the electronics and aerospace industries) and the
ability to allow some radio signals to pass whilst preventing others (eg privacy and security
applications) The work has allowed the Physical Layer Research Group to develop its measurement
capability so that the electromagnetic properties of nanostructured materials can be measured and
also to begin working on materials by fabricating a range of nano-particle based films
In Section 2 a review of the electromagnetic properties of materials and the extraction of
electromagnetic parameters from various measurements is discussed The software developed for
parameter extraction is then summarised In Section 3 the design and testing of a coaxial shielding
measurement jig is described In Section 4 the potential nano-structured materials that could be
fabricated to address currently funded research application areas are identified Section 5 provides
some concluding remarks and describes future and ongoing work in this area
2 Electromagnetic parameters of materials
Functionally the electromagnetic performance of materials are often specified in terms of their
transmission and reflection coefficients which define the amplitude and phase of plane
electromagnetic waves that propagate through and are reflected from a sample respectively The
proportion of the incident electromagnetic energy that is absorbed within the material (ie neither
reflected nor transmitted) may also be an important consideration in many application areas These
properties of the material depend on both its internal micro-structure and the overall macroscopic
shape of the material For the purposes of material characterisation a planar sample is often used
since the electromagnetic scattering and transmission from an infinite plane sheet of homogeneous
material is amenable to exact theoretical analysis thereby providing a solid reference for validation
of measurement procedures and numerical simulations
If probed by sufficiently high frequency electromagnetic waves the micro-structure of the material
can be discerned in the characteristics of the scattered waves This applies at different length scales
associated with the physical structure of the material The shortest length scale of interest
corresponds to the nano-scale level in which the atomic structure can be resolved Most
engineering materials have structure at larger length scales associated with their fabrication and
application For example carbon-fibre reinforced composites (CFCs) consist of filaments of carbon
with diameters of the order micro-meters embedded in a dielectric resin The microstructure
therefore has apertures between the fibres with a similar length scale that influences the
electromagnetic properties of the composite even at low frequencies
In many applications the frequencies of interest are far below the length-scale of the microstructure
and a homogenised view of the material can be taken averaging the electromagnetic fields at the
surface of the material to give simpler effective parameters for the material properties This
approach is called Effective Medium Theory (EMT) This is essentially a generalisation of the classical
macroscopic treatment of dielectric and magnetic materials in Maxwellrsquos electromagnetic theory by
Electromagnetic properties of nanostructured materials
University of York 4 10 July 2015
averaging over the atomic level electric and magnetic dipole moments caused by the induced charge
movements in the material when subjected to an external electromagnetic field This leads to the
definition of the classical electric permittivity and magnetic permeability of the material
In this chapter a brief review of the electromagnetic parameters is presented followed by a review
and implementation of the different methodologies that can be employed to extract material
parameters from different measurement system including the coaxial shielding jig described in
Section 3
21 Dielectric properties
Linear isotropic materials can be described by the introducing the electric flux density D that is
related to the electric field E via the complex permittivity ()Ƹߝ
۲() = ()Ƹ()۳ߝ = ε۳() + () = ε۳() + εχොக()۳()
Here ε is the permittivity of free-space P the electric polarisation vector and χොக() the electricsusceptibility The complex permittivity can be decomposed into real and imaginary parts
()Ƹߝ = minusᇱߝ jεᇱᇱ≝ Ƹ()εߝ
where the relative permittivity is
()Ƹߝ = εᇱminus jε
ᇱᇱ= 1 + χොக()ߝ
The real part characterises energy storage in material while the imaginary part characterisesloss due to the bound charge movement The loss tangent is defined ratio of energy lost percycle to energy stored per cycle and given by
tanߜக =εᇱᇱ
εᇱ
allowing the relative permittivity to be written
()Ƹߝ = εᇱ(1 minus j tanߜக)
Some materials have free ionic charges that respond to a DC electric field by producing aconduction current
۸() = ()ୈେ۳ߪ
The overall effective relative permittivity is then
()Ƹߝ = εᇱminus j൬ε
ᇱᇱ+ୈେߪε
൰
In real materials there are often partially bound charges which blur the distinction betweendielectric loss and conduction effects The AC conductivity may be written [Bake2005]
ߪ = minusᇱߪ jߪᇱᇱasymp ୈେߪ minus jߪᇱᇱ
The overall dielectric response is then characterised the a complex relative permittivity
()Ƹߝ = εᇱminus
ᇱᇱߪ
εminus jቆε
ᇱᇱ+ᇱߪ
εቇ
Electromagnetic properties of nanostructured materials
University of York 5 10 July 2015
In order for the material to have a causal time response the complex permittivity must
satisfy the Kramers-Kronig relations
εᇱ() minus ஶߝ = minus
2
ߨන
εߠᇱᇱ(ߠ)minus ε
ᇱᇱ()
minusଶߠ ଶdߠ
ஶ
εᇱᇱ() = minus
2
ߨන
εᇱ(ߠ) minus ε
ᇱ()
minusଶߠ ଶdߠ
ஶ
These can also be written in ldquoonce subtracted formrdquo
εᇱ() minus ε
ᇱ() = minus minus
ߨPVන
εᇱᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
ஶ
εᇱᇱ() minus ε
ᇱᇱ() = minus
ߨPVන
εᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
Various models for the frequency response of a material have been developed- some arelisted in Table 1
Model Dispersion Relation
Drude σ =
ଶ
1
ߛ + j=
ଶ
minusߛ j
ߛଶ + ଶ
Debye()ߝ = ஶߝ +
ߝ∆
1 + j
Lorentz ()ߝ = ஶߝ +ఌଶ
ఌଶ + Γఌω minus ଶ
Cole-Cole[Gabr1996] ()ߝ = ஶߝ +
ߝ∆1 + (j )ଵఈ
+ୈେߪjε
Table 1 Common dispersion models for dielectrics and conductors
22 Magnetic properties
In a completely analogous way the magnetic permeability of a material can be defined by
()Ƹߤ = minusᇱߤ jߤᇱᇱ= +ߤσlowast
j≝ ߤ()Ƹߤ
where σlowast is the magnetic conductance The relative permeability is then
()Ƹߤ = ߤᇱminus jߤ
ᇱᇱ= ߤ +σlowast
jߤ
Electromagnetic properties of nanostructured materials
University of York 6 10 July 2015
Figure 1 Interfacial transmission of TE and TM waves at z-normal boundary
23 Reflection and transmission at a plane interface
The reflection coefficient at an infinite plane interface between two different materials can be
determined from the boundary conditions on the electromagnetic field at the surface Consider a
plane-wave propagating in the z-x plane with wave vector
ܓ ൌ ௫ܠො ௭ܢො
in an isotropic medium with complex permittivity Ƹandߝ permeability Ƹߤ The wave can be
decomposed into transverse electric (TE) and transverse magnetic (TM) components
۳(ܚǢ ) ൌ Ǣܧe୨ܓήܡܚො
۶(ܚǢ ) ൌ Ǣܧ
1
Ƹߤe୨ܓήܚ(െ௭ܠො ௫ܢො)
and
۳ Ǣܚ) ) ൌ Ǣܧ e୨ܓήܚ൬ܠොെ
௫
௭ො൰ܢ
۶ Ǣܚ) ) ൌ Ǣܧ
Ƹߝ
௭e୨ܓήܡܚොǡ
where Ǣܧ and Ǣܧ
are the transverse field amplitudes and the dispersion relation is
௫ଶ ௭
ଶ ൌ ଶߤƸߝƸǤ
If the medium is lossless then the wave-vector is real and can be written
ܓ ൌ መܓ ൌ ොܠߠ) (ොܢߠ
Electromagnetic properties of nanostructured materials
University of York 7 10 July 2015
where is the angle between the z-axis and the wave vector and = ߝߤradic The total amplitudes of
the TE and TM fields are then related to the transverse field amplitudes by
ܧ = ܧ
ܧ = ܧ
cosߠ
The complete transverse fields can be written
۳ = ܧ
e୨௭e୨௫ܡො
۶ = minus
ܧ
ߟ
e୨௭e୨௫ܠො
and
۳ = ܧ
e୨௭e୨௫ܠො
۶ =
ܧ
ߟ
e୨௭e୨௫ܡො
where the transverse wave impedances are defined by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
Writing the total transverse field as
۳ = ܧ +ොܠ ܧ
ܡො
۶ = ܪ minusොܡ ܪ
ܠො
noting the minus sign for the x component of the TE magnetic field the propagation in the medium
is reduced to two uncoupled one-dimensional transmission line problems of the form
(ݖ)ܧ = ܧା(ݖ) + ܧ
(ݖ) = ܧାe୨௭ + ܧ
eା୨௭ = ܧା(ݖ)൫1 + Γ(ݖ)൯
(ݖ)ܪ = ܪା(ݖ) + ܪ
(ݖ) =1
ߟ൫ܧ
ାe୨௭minus ܧeା୨௭൯=
ܧା(ݖ)
ߟ൫1 minus Γ(ݖ)൯
where the e୨௫ phase factor has been suppressed This is illustrated in Figure 1 The propagation
of the forward and backward waves can be described by a propagation matrix
ܧା(ݖଵ)
ܧ(ଵݖ)
൨= e୨(௭మ௭భ) 0
0 e୨(௭మ௭భ)൨ܧା(ݖଶ)
ܧ(ଶݖ)
൨
while the total transverse fields propagate according to a ldquochain matrixrdquo given by
Electromagnetic properties of nanostructured materials
University of York 8 10 July 2015
(ଵݖ)ܧ(ଵݖ)ܪ
൨= cos ௭(ݖଶminus (ଵݖ jߟ sin ௭(ݖଶminus (ଵݖ
jߟଵ sin ௭(ݖଶminus (ଵݖ cos ௭(ݖଶminus (ଵݖ
൨(ଶݖ)ܧ(ଶݖ)ܪ
൨
The electric field reflection coefficient is
Γ(ݖ) =ܧ(ݖ)
ܧା(ݖ)
and propagates according to
Γ(ݖଵ) = Γ(ݖଵ)eଶ୨(௭మ௭భ)
while the wave impedance
(ݖ) =(ݖ)ܧ
(ݖ)ܪ= ߟ
1 + Γ(ݖ)
1 minus Γ(ݖ)
propagates as
(ଵݖ) = ߟ(ଶݖ) cos ௭(ݖଶminus (ଵݖ + jߟ sin ௭(ݖଶminus (ଵݖ
ߟ cos ௭(ݖଶminus (ଵݖ + j(ݖଶ) sin ௭(ݖଶminus (ଵݖ
Note that
Γ(ݖ) =(ݖ) minus ߟ(ݖ) + ߟ
At a plane interface between two semi-infinite media denoted left (L) and right (R) located at z = 0
the transverse electric and magnetic fields must be continuous Matching the phase in the x-
direction at the interface leads to Snellrsquos Law
௫ = ௫
If the left medium is lossless then
௫ = sinߠ= ඥߤƸߝƸ sinߠ = ௫
where is the angle in incidence and hence from the dispersion relationships
൫ ௫൯
ଶ+ ൫ ௭
൯ଶ
= ଶߤƸߝƸ ≝ ൫ ൯ଶ
we find that
௭ = ටଶߤƸߝƸ minus ൫ ௫
൯ଶ
= ඥଶߤƸߝƸ minus ( sinߠ)ଶ
For the left medium ௭ = cosߠ Matching the electric and magnetic fields either side of the
boundary
ܧ = ܧ
ା + ܧ = ܧ
ା + ܧ = ܧ
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
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௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
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ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
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eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
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Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
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ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
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or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
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௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 4 10 July 2015
averaging over the atomic level electric and magnetic dipole moments caused by the induced charge
movements in the material when subjected to an external electromagnetic field This leads to the
definition of the classical electric permittivity and magnetic permeability of the material
In this chapter a brief review of the electromagnetic parameters is presented followed by a review
and implementation of the different methodologies that can be employed to extract material
parameters from different measurement system including the coaxial shielding jig described in
Section 3
21 Dielectric properties
Linear isotropic materials can be described by the introducing the electric flux density D that is
related to the electric field E via the complex permittivity ()Ƹߝ
۲() = ()Ƹ()۳ߝ = ε۳() + () = ε۳() + εχොக()۳()
Here ε is the permittivity of free-space P the electric polarisation vector and χොக() the electricsusceptibility The complex permittivity can be decomposed into real and imaginary parts
()Ƹߝ = minusᇱߝ jεᇱᇱ≝ Ƹ()εߝ
where the relative permittivity is
()Ƹߝ = εᇱminus jε
ᇱᇱ= 1 + χොக()ߝ
The real part characterises energy storage in material while the imaginary part characterisesloss due to the bound charge movement The loss tangent is defined ratio of energy lost percycle to energy stored per cycle and given by
tanߜக =εᇱᇱ
εᇱ
allowing the relative permittivity to be written
()Ƹߝ = εᇱ(1 minus j tanߜக)
Some materials have free ionic charges that respond to a DC electric field by producing aconduction current
۸() = ()ୈେ۳ߪ
The overall effective relative permittivity is then
()Ƹߝ = εᇱminus j൬ε
ᇱᇱ+ୈେߪε
൰
In real materials there are often partially bound charges which blur the distinction betweendielectric loss and conduction effects The AC conductivity may be written [Bake2005]
ߪ = minusᇱߪ jߪᇱᇱasymp ୈେߪ minus jߪᇱᇱ
The overall dielectric response is then characterised the a complex relative permittivity
()Ƹߝ = εᇱminus
ᇱᇱߪ
εminus jቆε
ᇱᇱ+ᇱߪ
εቇ
Electromagnetic properties of nanostructured materials
University of York 5 10 July 2015
In order for the material to have a causal time response the complex permittivity must
satisfy the Kramers-Kronig relations
εᇱ() minus ஶߝ = minus
2
ߨන
εߠᇱᇱ(ߠ)minus ε
ᇱᇱ()
minusଶߠ ଶdߠ
ஶ
εᇱᇱ() = minus
2
ߨන
εᇱ(ߠ) minus ε
ᇱ()
minusଶߠ ଶdߠ
ஶ
These can also be written in ldquoonce subtracted formrdquo
εᇱ() minus ε
ᇱ() = minus minus
ߨPVන
εᇱᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
ஶ
εᇱᇱ() minus ε
ᇱᇱ() = minus
ߨPVන
εᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
Various models for the frequency response of a material have been developed- some arelisted in Table 1
Model Dispersion Relation
Drude σ =
ଶ
1
ߛ + j=
ଶ
minusߛ j
ߛଶ + ଶ
Debye()ߝ = ஶߝ +
ߝ∆
1 + j
Lorentz ()ߝ = ஶߝ +ఌଶ
ఌଶ + Γఌω minus ଶ
Cole-Cole[Gabr1996] ()ߝ = ஶߝ +
ߝ∆1 + (j )ଵఈ
+ୈେߪjε
Table 1 Common dispersion models for dielectrics and conductors
22 Magnetic properties
In a completely analogous way the magnetic permeability of a material can be defined by
()Ƹߤ = minusᇱߤ jߤᇱᇱ= +ߤσlowast
j≝ ߤ()Ƹߤ
where σlowast is the magnetic conductance The relative permeability is then
()Ƹߤ = ߤᇱminus jߤ
ᇱᇱ= ߤ +σlowast
jߤ
Electromagnetic properties of nanostructured materials
University of York 6 10 July 2015
Figure 1 Interfacial transmission of TE and TM waves at z-normal boundary
23 Reflection and transmission at a plane interface
The reflection coefficient at an infinite plane interface between two different materials can be
determined from the boundary conditions on the electromagnetic field at the surface Consider a
plane-wave propagating in the z-x plane with wave vector
ܓ ൌ ௫ܠො ௭ܢො
in an isotropic medium with complex permittivity Ƹandߝ permeability Ƹߤ The wave can be
decomposed into transverse electric (TE) and transverse magnetic (TM) components
۳(ܚǢ ) ൌ Ǣܧe୨ܓήܡܚො
۶(ܚǢ ) ൌ Ǣܧ
1
Ƹߤe୨ܓήܚ(െ௭ܠො ௫ܢො)
and
۳ Ǣܚ) ) ൌ Ǣܧ e୨ܓήܚ൬ܠොെ
௫
௭ො൰ܢ
۶ Ǣܚ) ) ൌ Ǣܧ
Ƹߝ
௭e୨ܓήܡܚොǡ
where Ǣܧ and Ǣܧ
are the transverse field amplitudes and the dispersion relation is
௫ଶ ௭
ଶ ൌ ଶߤƸߝƸǤ
If the medium is lossless then the wave-vector is real and can be written
ܓ ൌ መܓ ൌ ොܠߠ) (ොܢߠ
Electromagnetic properties of nanostructured materials
University of York 7 10 July 2015
where is the angle between the z-axis and the wave vector and = ߝߤradic The total amplitudes of
the TE and TM fields are then related to the transverse field amplitudes by
ܧ = ܧ
ܧ = ܧ
cosߠ
The complete transverse fields can be written
۳ = ܧ
e୨௭e୨௫ܡො
۶ = minus
ܧ
ߟ
e୨௭e୨௫ܠො
and
۳ = ܧ
e୨௭e୨௫ܠො
۶ =
ܧ
ߟ
e୨௭e୨௫ܡො
where the transverse wave impedances are defined by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
Writing the total transverse field as
۳ = ܧ +ොܠ ܧ
ܡො
۶ = ܪ minusොܡ ܪ
ܠො
noting the minus sign for the x component of the TE magnetic field the propagation in the medium
is reduced to two uncoupled one-dimensional transmission line problems of the form
(ݖ)ܧ = ܧା(ݖ) + ܧ
(ݖ) = ܧାe୨௭ + ܧ
eା୨௭ = ܧା(ݖ)൫1 + Γ(ݖ)൯
(ݖ)ܪ = ܪା(ݖ) + ܪ
(ݖ) =1
ߟ൫ܧ
ାe୨௭minus ܧeା୨௭൯=
ܧା(ݖ)
ߟ൫1 minus Γ(ݖ)൯
where the e୨௫ phase factor has been suppressed This is illustrated in Figure 1 The propagation
of the forward and backward waves can be described by a propagation matrix
ܧା(ݖଵ)
ܧ(ଵݖ)
൨= e୨(௭మ௭భ) 0
0 e୨(௭మ௭భ)൨ܧା(ݖଶ)
ܧ(ଶݖ)
൨
while the total transverse fields propagate according to a ldquochain matrixrdquo given by
Electromagnetic properties of nanostructured materials
University of York 8 10 July 2015
(ଵݖ)ܧ(ଵݖ)ܪ
൨= cos ௭(ݖଶminus (ଵݖ jߟ sin ௭(ݖଶminus (ଵݖ
jߟଵ sin ௭(ݖଶminus (ଵݖ cos ௭(ݖଶminus (ଵݖ
൨(ଶݖ)ܧ(ଶݖ)ܪ
൨
The electric field reflection coefficient is
Γ(ݖ) =ܧ(ݖ)
ܧା(ݖ)
and propagates according to
Γ(ݖଵ) = Γ(ݖଵ)eଶ୨(௭మ௭భ)
while the wave impedance
(ݖ) =(ݖ)ܧ
(ݖ)ܪ= ߟ
1 + Γ(ݖ)
1 minus Γ(ݖ)
propagates as
(ଵݖ) = ߟ(ଶݖ) cos ௭(ݖଶminus (ଵݖ + jߟ sin ௭(ݖଶminus (ଵݖ
ߟ cos ௭(ݖଶminus (ଵݖ + j(ݖଶ) sin ௭(ݖଶminus (ଵݖ
Note that
Γ(ݖ) =(ݖ) minus ߟ(ݖ) + ߟ
At a plane interface between two semi-infinite media denoted left (L) and right (R) located at z = 0
the transverse electric and magnetic fields must be continuous Matching the phase in the x-
direction at the interface leads to Snellrsquos Law
௫ = ௫
If the left medium is lossless then
௫ = sinߠ= ඥߤƸߝƸ sinߠ = ௫
where is the angle in incidence and hence from the dispersion relationships
൫ ௫൯
ଶ+ ൫ ௭
൯ଶ
= ଶߤƸߝƸ ≝ ൫ ൯ଶ
we find that
௭ = ටଶߤƸߝƸ minus ൫ ௫
൯ଶ
= ඥଶߤƸߝƸ minus ( sinߠ)ଶ
For the left medium ௭ = cosߠ Matching the electric and magnetic fields either side of the
boundary
ܧ = ܧ
ା + ܧ = ܧ
ା + ܧ = ܧ
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
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ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
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௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
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ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
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=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
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6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
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Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
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Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
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Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
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Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 5 10 July 2015
In order for the material to have a causal time response the complex permittivity must
satisfy the Kramers-Kronig relations
εᇱ() minus ஶߝ = minus
2
ߨන
εߠᇱᇱ(ߠ)minus ε
ᇱᇱ()
minusଶߠ ଶdߠ
ஶ
εᇱᇱ() = minus
2
ߨන
εᇱ(ߠ) minus ε
ᇱ()
minusଶߠ ଶdߠ
ஶ
These can also be written in ldquoonce subtracted formrdquo
εᇱ() minus ε
ᇱ() = minus minus
ߨPVන
εᇱᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
ஶ
εᇱᇱ() minus ε
ᇱᇱ() = minus
ߨPVන
εᇱ(ߠ)
minusߠ) minusߠ)( )dߠ
ஶ
Various models for the frequency response of a material have been developed- some arelisted in Table 1
Model Dispersion Relation
Drude σ =
ଶ
1
ߛ + j=
ଶ
minusߛ j
ߛଶ + ଶ
Debye()ߝ = ஶߝ +
ߝ∆
1 + j
Lorentz ()ߝ = ஶߝ +ఌଶ
ఌଶ + Γఌω minus ଶ
Cole-Cole[Gabr1996] ()ߝ = ஶߝ +
ߝ∆1 + (j )ଵఈ
+ୈେߪjε
Table 1 Common dispersion models for dielectrics and conductors
22 Magnetic properties
In a completely analogous way the magnetic permeability of a material can be defined by
()Ƹߤ = minusᇱߤ jߤᇱᇱ= +ߤσlowast
j≝ ߤ()Ƹߤ
where σlowast is the magnetic conductance The relative permeability is then
()Ƹߤ = ߤᇱminus jߤ
ᇱᇱ= ߤ +σlowast
jߤ
Electromagnetic properties of nanostructured materials
University of York 6 10 July 2015
Figure 1 Interfacial transmission of TE and TM waves at z-normal boundary
23 Reflection and transmission at a plane interface
The reflection coefficient at an infinite plane interface between two different materials can be
determined from the boundary conditions on the electromagnetic field at the surface Consider a
plane-wave propagating in the z-x plane with wave vector
ܓ ൌ ௫ܠො ௭ܢො
in an isotropic medium with complex permittivity Ƹandߝ permeability Ƹߤ The wave can be
decomposed into transverse electric (TE) and transverse magnetic (TM) components
۳(ܚǢ ) ൌ Ǣܧe୨ܓήܡܚො
۶(ܚǢ ) ൌ Ǣܧ
1
Ƹߤe୨ܓήܚ(െ௭ܠො ௫ܢො)
and
۳ Ǣܚ) ) ൌ Ǣܧ e୨ܓήܚ൬ܠොെ
௫
௭ො൰ܢ
۶ Ǣܚ) ) ൌ Ǣܧ
Ƹߝ
௭e୨ܓήܡܚොǡ
where Ǣܧ and Ǣܧ
are the transverse field amplitudes and the dispersion relation is
௫ଶ ௭
ଶ ൌ ଶߤƸߝƸǤ
If the medium is lossless then the wave-vector is real and can be written
ܓ ൌ መܓ ൌ ොܠߠ) (ොܢߠ
Electromagnetic properties of nanostructured materials
University of York 7 10 July 2015
where is the angle between the z-axis and the wave vector and = ߝߤradic The total amplitudes of
the TE and TM fields are then related to the transverse field amplitudes by
ܧ = ܧ
ܧ = ܧ
cosߠ
The complete transverse fields can be written
۳ = ܧ
e୨௭e୨௫ܡො
۶ = minus
ܧ
ߟ
e୨௭e୨௫ܠො
and
۳ = ܧ
e୨௭e୨௫ܠො
۶ =
ܧ
ߟ
e୨௭e୨௫ܡො
where the transverse wave impedances are defined by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
Writing the total transverse field as
۳ = ܧ +ොܠ ܧ
ܡො
۶ = ܪ minusොܡ ܪ
ܠො
noting the minus sign for the x component of the TE magnetic field the propagation in the medium
is reduced to two uncoupled one-dimensional transmission line problems of the form
(ݖ)ܧ = ܧା(ݖ) + ܧ
(ݖ) = ܧାe୨௭ + ܧ
eା୨௭ = ܧା(ݖ)൫1 + Γ(ݖ)൯
(ݖ)ܪ = ܪା(ݖ) + ܪ
(ݖ) =1
ߟ൫ܧ
ାe୨௭minus ܧeା୨௭൯=
ܧା(ݖ)
ߟ൫1 minus Γ(ݖ)൯
where the e୨௫ phase factor has been suppressed This is illustrated in Figure 1 The propagation
of the forward and backward waves can be described by a propagation matrix
ܧା(ݖଵ)
ܧ(ଵݖ)
൨= e୨(௭మ௭భ) 0
0 e୨(௭మ௭భ)൨ܧା(ݖଶ)
ܧ(ଶݖ)
൨
while the total transverse fields propagate according to a ldquochain matrixrdquo given by
Electromagnetic properties of nanostructured materials
University of York 8 10 July 2015
(ଵݖ)ܧ(ଵݖ)ܪ
൨= cos ௭(ݖଶminus (ଵݖ jߟ sin ௭(ݖଶminus (ଵݖ
jߟଵ sin ௭(ݖଶminus (ଵݖ cos ௭(ݖଶminus (ଵݖ
൨(ଶݖ)ܧ(ଶݖ)ܪ
൨
The electric field reflection coefficient is
Γ(ݖ) =ܧ(ݖ)
ܧା(ݖ)
and propagates according to
Γ(ݖଵ) = Γ(ݖଵ)eଶ୨(௭మ௭భ)
while the wave impedance
(ݖ) =(ݖ)ܧ
(ݖ)ܪ= ߟ
1 + Γ(ݖ)
1 minus Γ(ݖ)
propagates as
(ଵݖ) = ߟ(ଶݖ) cos ௭(ݖଶminus (ଵݖ + jߟ sin ௭(ݖଶminus (ଵݖ
ߟ cos ௭(ݖଶminus (ଵݖ + j(ݖଶ) sin ௭(ݖଶminus (ଵݖ
Note that
Γ(ݖ) =(ݖ) minus ߟ(ݖ) + ߟ
At a plane interface between two semi-infinite media denoted left (L) and right (R) located at z = 0
the transverse electric and magnetic fields must be continuous Matching the phase in the x-
direction at the interface leads to Snellrsquos Law
௫ = ௫
If the left medium is lossless then
௫ = sinߠ= ඥߤƸߝƸ sinߠ = ௫
where is the angle in incidence and hence from the dispersion relationships
൫ ௫൯
ଶ+ ൫ ௭
൯ଶ
= ଶߤƸߝƸ ≝ ൫ ൯ଶ
we find that
௭ = ටଶߤƸߝƸ minus ൫ ௫
൯ଶ
= ඥଶߤƸߝƸ minus ( sinߠ)ଶ
For the left medium ௭ = cosߠ Matching the electric and magnetic fields either side of the
boundary
ܧ = ܧ
ା + ܧ = ܧ
ା + ܧ = ܧ
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
University of York 15 10 July 2015
ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
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≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 6 10 July 2015
Figure 1 Interfacial transmission of TE and TM waves at z-normal boundary
23 Reflection and transmission at a plane interface
The reflection coefficient at an infinite plane interface between two different materials can be
determined from the boundary conditions on the electromagnetic field at the surface Consider a
plane-wave propagating in the z-x plane with wave vector
ܓ ൌ ௫ܠො ௭ܢො
in an isotropic medium with complex permittivity Ƹandߝ permeability Ƹߤ The wave can be
decomposed into transverse electric (TE) and transverse magnetic (TM) components
۳(ܚǢ ) ൌ Ǣܧe୨ܓήܡܚො
۶(ܚǢ ) ൌ Ǣܧ
1
Ƹߤe୨ܓήܚ(െ௭ܠො ௫ܢො)
and
۳ Ǣܚ) ) ൌ Ǣܧ e୨ܓήܚ൬ܠොെ
௫
௭ො൰ܢ
۶ Ǣܚ) ) ൌ Ǣܧ
Ƹߝ
௭e୨ܓήܡܚොǡ
where Ǣܧ and Ǣܧ
are the transverse field amplitudes and the dispersion relation is
௫ଶ ௭
ଶ ൌ ଶߤƸߝƸǤ
If the medium is lossless then the wave-vector is real and can be written
ܓ ൌ መܓ ൌ ොܠߠ) (ොܢߠ
Electromagnetic properties of nanostructured materials
University of York 7 10 July 2015
where is the angle between the z-axis and the wave vector and = ߝߤradic The total amplitudes of
the TE and TM fields are then related to the transverse field amplitudes by
ܧ = ܧ
ܧ = ܧ
cosߠ
The complete transverse fields can be written
۳ = ܧ
e୨௭e୨௫ܡො
۶ = minus
ܧ
ߟ
e୨௭e୨௫ܠො
and
۳ = ܧ
e୨௭e୨௫ܠො
۶ =
ܧ
ߟ
e୨௭e୨௫ܡො
where the transverse wave impedances are defined by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
Writing the total transverse field as
۳ = ܧ +ොܠ ܧ
ܡො
۶ = ܪ minusොܡ ܪ
ܠො
noting the minus sign for the x component of the TE magnetic field the propagation in the medium
is reduced to two uncoupled one-dimensional transmission line problems of the form
(ݖ)ܧ = ܧା(ݖ) + ܧ
(ݖ) = ܧାe୨௭ + ܧ
eା୨௭ = ܧା(ݖ)൫1 + Γ(ݖ)൯
(ݖ)ܪ = ܪା(ݖ) + ܪ
(ݖ) =1
ߟ൫ܧ
ାe୨௭minus ܧeା୨௭൯=
ܧା(ݖ)
ߟ൫1 minus Γ(ݖ)൯
where the e୨௫ phase factor has been suppressed This is illustrated in Figure 1 The propagation
of the forward and backward waves can be described by a propagation matrix
ܧା(ݖଵ)
ܧ(ଵݖ)
൨= e୨(௭మ௭భ) 0
0 e୨(௭మ௭భ)൨ܧା(ݖଶ)
ܧ(ଶݖ)
൨
while the total transverse fields propagate according to a ldquochain matrixrdquo given by
Electromagnetic properties of nanostructured materials
University of York 8 10 July 2015
(ଵݖ)ܧ(ଵݖ)ܪ
൨= cos ௭(ݖଶminus (ଵݖ jߟ sin ௭(ݖଶminus (ଵݖ
jߟଵ sin ௭(ݖଶminus (ଵݖ cos ௭(ݖଶminus (ଵݖ
൨(ଶݖ)ܧ(ଶݖ)ܪ
൨
The electric field reflection coefficient is
Γ(ݖ) =ܧ(ݖ)
ܧା(ݖ)
and propagates according to
Γ(ݖଵ) = Γ(ݖଵ)eଶ୨(௭మ௭భ)
while the wave impedance
(ݖ) =(ݖ)ܧ
(ݖ)ܪ= ߟ
1 + Γ(ݖ)
1 minus Γ(ݖ)
propagates as
(ଵݖ) = ߟ(ଶݖ) cos ௭(ݖଶminus (ଵݖ + jߟ sin ௭(ݖଶminus (ଵݖ
ߟ cos ௭(ݖଶminus (ଵݖ + j(ݖଶ) sin ௭(ݖଶminus (ଵݖ
Note that
Γ(ݖ) =(ݖ) minus ߟ(ݖ) + ߟ
At a plane interface between two semi-infinite media denoted left (L) and right (R) located at z = 0
the transverse electric and magnetic fields must be continuous Matching the phase in the x-
direction at the interface leads to Snellrsquos Law
௫ = ௫
If the left medium is lossless then
௫ = sinߠ= ඥߤƸߝƸ sinߠ = ௫
where is the angle in incidence and hence from the dispersion relationships
൫ ௫൯
ଶ+ ൫ ௭
൯ଶ
= ଶߤƸߝƸ ≝ ൫ ൯ଶ
we find that
௭ = ටଶߤƸߝƸ minus ൫ ௫
൯ଶ
= ඥଶߤƸߝƸ minus ( sinߠ)ଶ
For the left medium ௭ = cosߠ Matching the electric and magnetic fields either side of the
boundary
ܧ = ܧ
ା + ܧ = ܧ
ା + ܧ = ܧ
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
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ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
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ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
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=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
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6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
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Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
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Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
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Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
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Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 7 10 July 2015
where is the angle between the z-axis and the wave vector and = ߝߤradic The total amplitudes of
the TE and TM fields are then related to the transverse field amplitudes by
ܧ = ܧ
ܧ = ܧ
cosߠ
The complete transverse fields can be written
۳ = ܧ
e୨௭e୨௫ܡො
۶ = minus
ܧ
ߟ
e୨௭e୨௫ܠො
and
۳ = ܧ
e୨௭e୨௫ܠො
۶ =
ܧ
ߟ
e୨௭e୨௫ܡො
where the transverse wave impedances are defined by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
Writing the total transverse field as
۳ = ܧ +ොܠ ܧ
ܡො
۶ = ܪ minusොܡ ܪ
ܠො
noting the minus sign for the x component of the TE magnetic field the propagation in the medium
is reduced to two uncoupled one-dimensional transmission line problems of the form
(ݖ)ܧ = ܧା(ݖ) + ܧ
(ݖ) = ܧାe୨௭ + ܧ
eା୨௭ = ܧା(ݖ)൫1 + Γ(ݖ)൯
(ݖ)ܪ = ܪା(ݖ) + ܪ
(ݖ) =1
ߟ൫ܧ
ାe୨௭minus ܧeା୨௭൯=
ܧା(ݖ)
ߟ൫1 minus Γ(ݖ)൯
where the e୨௫ phase factor has been suppressed This is illustrated in Figure 1 The propagation
of the forward and backward waves can be described by a propagation matrix
ܧା(ݖଵ)
ܧ(ଵݖ)
൨= e୨(௭మ௭భ) 0
0 e୨(௭మ௭భ)൨ܧା(ݖଶ)
ܧ(ଶݖ)
൨
while the total transverse fields propagate according to a ldquochain matrixrdquo given by
Electromagnetic properties of nanostructured materials
University of York 8 10 July 2015
(ଵݖ)ܧ(ଵݖ)ܪ
൨= cos ௭(ݖଶminus (ଵݖ jߟ sin ௭(ݖଶminus (ଵݖ
jߟଵ sin ௭(ݖଶminus (ଵݖ cos ௭(ݖଶminus (ଵݖ
൨(ଶݖ)ܧ(ଶݖ)ܪ
൨
The electric field reflection coefficient is
Γ(ݖ) =ܧ(ݖ)
ܧା(ݖ)
and propagates according to
Γ(ݖଵ) = Γ(ݖଵ)eଶ୨(௭మ௭భ)
while the wave impedance
(ݖ) =(ݖ)ܧ
(ݖ)ܪ= ߟ
1 + Γ(ݖ)
1 minus Γ(ݖ)
propagates as
(ଵݖ) = ߟ(ଶݖ) cos ௭(ݖଶminus (ଵݖ + jߟ sin ௭(ݖଶminus (ଵݖ
ߟ cos ௭(ݖଶminus (ଵݖ + j(ݖଶ) sin ௭(ݖଶminus (ଵݖ
Note that
Γ(ݖ) =(ݖ) minus ߟ(ݖ) + ߟ
At a plane interface between two semi-infinite media denoted left (L) and right (R) located at z = 0
the transverse electric and magnetic fields must be continuous Matching the phase in the x-
direction at the interface leads to Snellrsquos Law
௫ = ௫
If the left medium is lossless then
௫ = sinߠ= ඥߤƸߝƸ sinߠ = ௫
where is the angle in incidence and hence from the dispersion relationships
൫ ௫൯
ଶ+ ൫ ௭
൯ଶ
= ଶߤƸߝƸ ≝ ൫ ൯ଶ
we find that
௭ = ටଶߤƸߝƸ minus ൫ ௫
൯ଶ
= ඥଶߤƸߝƸ minus ( sinߠ)ଶ
For the left medium ௭ = cosߠ Matching the electric and magnetic fields either side of the
boundary
ܧ = ܧ
ା + ܧ = ܧ
ା + ܧ = ܧ
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
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௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
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ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
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eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
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Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
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ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
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௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 8 10 July 2015
(ଵݖ)ܧ(ଵݖ)ܪ
൨= cos ௭(ݖଶminus (ଵݖ jߟ sin ௭(ݖଶminus (ଵݖ
jߟଵ sin ௭(ݖଶminus (ଵݖ cos ௭(ݖଶminus (ଵݖ
൨(ଶݖ)ܧ(ଶݖ)ܪ
൨
The electric field reflection coefficient is
Γ(ݖ) =ܧ(ݖ)
ܧା(ݖ)
and propagates according to
Γ(ݖଵ) = Γ(ݖଵ)eଶ୨(௭మ௭భ)
while the wave impedance
(ݖ) =(ݖ)ܧ
(ݖ)ܪ= ߟ
1 + Γ(ݖ)
1 minus Γ(ݖ)
propagates as
(ଵݖ) = ߟ(ଶݖ) cos ௭(ݖଶminus (ଵݖ + jߟ sin ௭(ݖଶminus (ଵݖ
ߟ cos ௭(ݖଶminus (ଵݖ + j(ݖଶ) sin ௭(ݖଶminus (ଵݖ
Note that
Γ(ݖ) =(ݖ) minus ߟ(ݖ) + ߟ
At a plane interface between two semi-infinite media denoted left (L) and right (R) located at z = 0
the transverse electric and magnetic fields must be continuous Matching the phase in the x-
direction at the interface leads to Snellrsquos Law
௫ = ௫
If the left medium is lossless then
௫ = sinߠ= ඥߤƸߝƸ sinߠ = ௫
where is the angle in incidence and hence from the dispersion relationships
൫ ௫൯
ଶ+ ൫ ௭
൯ଶ
= ଶߤƸߝƸ ≝ ൫ ൯ଶ
we find that
௭ = ටଶߤƸߝƸ minus ൫ ௫
൯ଶ
= ඥଶߤƸߝƸ minus ( sinߠ)ଶ
For the left medium ௭ = cosߠ Matching the electric and magnetic fields either side of the
boundary
ܧ = ܧ
ା + ܧ = ܧ
ା + ܧ = ܧ
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
University of York 15 10 July 2015
ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
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௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
University of York 27 10 July 2015
This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 9 10 July 2015
ܪ =
1
ߟ൫ܧ
ା minus ܧ൯=
1
ߟ൫ܧ
ା minus ܧ൯= ܪ
leads to a matching matrix condition at the interface
ቈܧା
ܧ=
1
Ԧ
1 ԦߩԦߩ 1
൨ቈܧା
ܧ
where the interfacial reflection and transmission coefficients for incidence from the left are given by
Ԧߩ =ߟ minus ߟ
ߟ + ߟ
Ԧ =ߟ2
ߟ + ߟ
The inverse matching condition is
ቈܧା
ܧ=
1
ശ
1 ശߩശߩ 1
൨ቈܧା
ܧ
where
ശߩ =ߟminus ߟ
ߟ + ߟ
ശ =ߟ2
ߟ + ߟ
and
Ԧ = 1 + Ԧߩ Ԧߩ = ശߩminus ശ = 1 + ശߩ = 1 minus Ԧߩ Ԧ ശ = 1 minus ଶ(Ԧߩ)
Note that the wave impedance is continuous across the interface
=ܧ
ܪ
=ܧ
ܪ
=
The reflection coefficients on either side of the boundary are related by
Γ =ܧ
ܧା
=Ԧߩ + Γ
1 + ԦΓߩhArr Γ =
ܧ
ܧା
=ശߩ + Γ
1 + ശΓߩ
The scattering matrix for the interface is given by
ቈܧ
ܧା=
Ԧߩ ശԦ ശߩ
൨ቈܧା
ܧ
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
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ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
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ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
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=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
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6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
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Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
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Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
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Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
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Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 10 10 July 2015
Figure 2 Oblique incidence on a slab in terms of transverse fields
24 Reflection and transmission of a TEM wave from a slab
We now consider the reflection and transmission from a slab of material formed by two interfaces as
shown in Figure 2 The interfacial reflection and transmission coefficients for the two interfaces are
ԦǢଵߩ =Ǣଵߟ െ ǢߟǢଵߟ Ǣߟ
ԦǢଶߩ =Ǣୠߟ െ ǢଵߟǢୠߟ Ǣଵߟ
ԦǢଵ ൌ ͳ ԦǢଵߩ
ԦǢଶ ൌ ͳ ԦǢଶߩ
where
Ǣߟ =
Ƹߤ
௭Ǣ
Ǣߟ =
௭Ǣ
Ƹߝ
௭Ǣ= ටଶߤƸߝƸെ ൫ ௫Ǣ൯ଶ
= ඥଶߤƸߝƸminus (ୟߠୟ)ଶ
If the medium either side of the slab is lossless then phase matching in the x-direction gives
௫ୟ ൌ ௫
ୠ ୟߠୟ ൌ ୠߠୠ
Specifically if the medium on either side of the slab is the same
௭Ǣ = ඥଶߤୟߝୟminus (ୟߠୟ)ଶ ൌ ඥߤୟߝୟඥ1 minus ଶ(ୟߠ)
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
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eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
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Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
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ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
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௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
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ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
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=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
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pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
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DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 11 10 July 2015
௭ଵ = ඥଶߤƸଵߝƸଵminus (ୟsinߠୟ)ଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (sinߠୟ)ଶ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
where ෝଵ = ඥߤƸଵߝƸଵ fraslୟߝୟߤ is the relative refractive index of the slab relative to the material either
side
The matching and propagation matrices for the two interfaces and one layer are
ቈଵܧା
ଵܧ=
1
Ԧଵቈ
1 Ԧଵߩ
Ԧଵߩ 1ቈଵܧା
ଵܧ
ቈଵܧା
ଵܧ= e
୨భ(௭మ௭భ) 00 e୨భ(௭మ௭భ)
൨ቈଶܧା
ଶܧ
ቈଶܧା
ଶܧ=
1
Ԧଶቈ
1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
which can be put together to give
ቈଵܧା
ଵܧ=
1
Ԧଵ Ԧଶቈ
1 Ԧଵߩ
Ԧଵߩ 1e
୨ఋభ 00 e୨ఋభ
൨ቈ1 Ԧଶߩ
Ԧଶߩ 1ቈଶܧା
ଶܧ
where
≝ଵߜ ௭ଵ(ݖଶminus (ଵݖ ≝ ௭ଵ ଵ
Changing the dependent and independent variables in the linear system leads to the scattering
matrix
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ቈଵܧା
ଶܧ=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଵܧା
ଶܧ≝ ଵቈ
ଵܧା
ଶܧ
where
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
Γ = minusԦଶߩ + Ԧଵeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଶߩ + ശଵeଶ୨ఋభߩ
1 + ശଶeଶ୨ఋభߩശଵߩ
ሬ=൫1 minus Ԧଵߩ
ଶ ൯
Ԧଵ
൫1 minus Ԧଵߩଶ ൯
Ԧଶ
e୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ=
ശଵശଶe୨ఋభ
1 + ശଶeଶ୨ఋభߩശଵߩ
An alternative arrangement of the linear equations gives the transmission scattering matrix for the
slab
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
University of York 15 10 July 2015
ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 12 10 July 2015
ቈଵܧ
ଵܧା=
1
ሬቈminusdet ଵ Γ
minusΓ 1ቈଶܧ
ଶܧା=
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨ቈଶܧ
ଶܧା= ധ
ଵቈଶܧ
ଶܧା
ቈଶܧ
ଶܧା=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
ቈଵܧ
ଵܧା
ധଵ =
ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଵଵቈminusdet ଵ ଵଵଵ
minus ଶଶଵ 1
ଵ = ଵଵଵ ଵଶଵ
ଶଵଵ ଶଶଵ൨=
1
ଶଶଵቈ ଵଶଵ det ധଵ1 minus ଶଵଵ
det ଵ = ΓΓ minus ሬሬ
det ଵ = ΓΓ minus ሬሬ
det ധଵ = ሬ
Note that for a matched section of line
det ଵ = minusሬሬ
and therefore
ധଵ =
1
ሬቈdet ଵ Γ
minusΓ 1=
1
e୨ఋభeଶ୨ఋభ 0
0 1൨= e
୨ఋభ 00 e୨ఋభ
൨
The complex wave vector in a lossy medium can be written in terms of propagation and attenuation
coefficients as
ଵܓ = ௫ଵܠො+ ௭ܢො= minusଵࢼ jࢻଵ = ൫ߚ௫ଵminus +ොܠ௫ଵ൯ߙ ൫ߚ௭ଵminus ොܢ௭ଵ൯ߙ
subject to
ଵܓ ∙ ଵܓ = ඥߤƸଵߝƸଵ
The spatial variation of the internal fields in the slab therefore has the form
e୨௭e୨௫ = e୨൫ఉభఈభ൯௭e୨൫ఉభఈభ൯௫ = e൫ఈభ௭ାఈభ௫൯e୨൫ఉభ௭ାఉభ௫൯
The condition for zero reflection Γ rarr 0 from the slab is
Ԧଵߩ + Ԧଶeଶ୨ఋభߩ = 0
or
eଶ୨ఋభ = eଶఈభభeଶ୨ఉభభ = minusԦଵߩ
Ԧଶߩ
For a lossless slab with a lossless medium at either side at normal incidence in a TEM wave structure
Ԧଵߩ fraslԦଶߩ is real so this condition requires either
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
University of York 15 10 July 2015
ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 13 10 July 2015
eଶ୨ఉభభ = 1 andߩԦଶ = Ԧଵߩminus
or
eଶ୨ఉభభ = minus1 andߩԦଶ = Ԧଵߩ
The first case corresponds to the slab being a multiple of a half-wavelength (in the medium) thick
and further requires the medium to be the same on either side of the slab
௭ଵߚ2 ଵ =ߨ2
ଵߣଵ = ߟandߨ2 = ߟ
The second case corresponds to the slab being a quarter-wavelength (in the medium thick) and
imposes a matching condition on the transverse impedances
௭ଵߚ2 ଵ =ଶగ
ఒభଵ = (2 + ଵߟandߨ(1
ଶ = ߟߟ
In this lossless case zero reflection requires total transmission Γ rarr 0 rArr ሬ= 1 since there is no
absorption in the slab
Now consider illumination from the left
ቈଵܧ
ଶܧା= Γ ሬ
ሬ Γ൨ଵܧା
0൨
so that
ଵܧ = Γܧଵ
ା
ଶܧା = ሬܧଵ
ା
and the reflected and transmitted power are
ሬ =
1
ୟߟหܧଵ
หଶ
=1
ୟߟหΓห
ଶหܧଵ
ାหଶ≝ ℛሬ
หܧଵାห
ଶ
ୟߟ= ℛሬሬ୧୬
ሬ୲ୟ୬ୱ =
1
ୠߟหܧଶ
ାหଶ
=1
ୠߟหሬห
ଶหܧଵ
ାหଶ≝ ሬ
หܧଵାห
ଶ
ୟߟ= ሬሬ
୧୬
where the reflectance transmittance and absorbance of the sample are respectively
ℛሬ≝ሬ
ሬ୧୬
= หΓหଶ
≝ሬ୲ୟ୬ୱ
ሬ୧୬
=ୟߟ
ୠߟหሬห
ଶ
≝ሬ୧୬ minus ሬ
minus ሬ୲ୟ୬ୱ
ሬ୧୬
= 1 minus ℛሬminus ሬ= 1 minus หΓหଶminusୟߟ
ୠߟหሬห
ଶ
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
University of York 15 10 July 2015
ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
University of York 22 10 July 2015
For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
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ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
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=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 14 10 July 2015
Here we have assumed that the left and right media are lossless If the left and right media are the
same then the ratio of intrinsic impedances is unity
25 Reflection and transmission of a TETM wave from a slab in a waveguide
For transverse electric (TE) and transverse magnetic (TM) waves the formulation is essentially the
same as the oblique incidence TEM case with a redefinition of transverse impedances and dispersion
relation
௭= ට ଶminus ୡ
ଶ = ටଶߤƸߝƸminus ୡଶ
ߟ ≝
Ƹߤ
௭
ߟ ≝
௭
Ƹߝ
Typically TE10 mode is used for material characterisation If the medium either side of the slab is the
same and lossless we have
௭ୟ = ට ୟଶminus ୡ
ଶ = ୟඥ1 minus ( ୡ ୟfrasl )ଶ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ
where
ୡ≝ୡ
ඥߤୟߝୟ≝ ୟ ୡ≝ ୟ
ߨ2
ୡߣ
Then
௭ଵ = ටଶߤƸଵߝƸଵminus ୡଶ = ඥߤୟߝୟටߤƸଵߝƸଵminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ
Also for TE waves only
ୟߟ ≝
Ƹୟߤ
௭ୟ=
ඥߤୟ fraslୟߝ
ඥ1 minus (ୡ frasl )ଶ=
ୟߟ
ඥ1 minus (ୡ frasl )ଶ
௭ߟ = Ƹߤ
26 Contributions to the sample transmission
The transmission through a slab can be factorised into three components due to the initial reflection
from the front face absorption through the slab and multiple reflections
ሬ= ሬ ሬୟୠୱ
ሬ୫ ୳୪୲୧
where
ሬ = 1 minus Ԧଵߩ
ଶ =ߟ4
൫ߟ + 1൯ଶ
Electromagnetic properties of nanostructured materials
University of York 15 10 July 2015
ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
University of York 22 10 July 2015
For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
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6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
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Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
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Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 15 10 July 2015
ሬୟୠୱ = = e୨ఋభ = e୨൫ఉభఈభ൯భ = eఈభభe୨ఉభభ
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
= ൫ߩԦଵ൯ଶ
ஶ
ୀ
For samples with large absorption || ≪ 1 and ሬ୫ ୳୪୲୧ is small Note that the overall reflection
coefficient likewise contains three terms The first Ԧଵߩ is the reflection from the front face of the
sample the second 1 minus ଶ accounts for the initial reflection from the back face and is small if
absorption in the sample is significant The third term 1 1 minus Ԧଵߩଶ ଶfrasl is a multiple reflection term
that is only important for thin or low loss materials
For a good conductor with no magnetic losses
ߟ =1
ߟඨƸଵߤƸଵߝ
=1
ߟඨ
ଵߤminusଵߝ ଵߪ frasl
asymp (1 + )ඨଵߤߝ
ଵߪ2≪ 1
and hence
ሬ = ߟ4 = 4(1 + )ඨ
ଵߤߝߨ
ଵߪ= 4(1 + )ඨ
ଵߤߝߨ
େ୳ߪଵߪ= 4(1 + )ඨ
ߝߨେ୳ߪ
ඨଵߤ
ଵߪ
where େ୳ߪ =58 MSm Taking the magnitude in decibels [Paul1992 eqn (1131)]
หሬ ห[dB] = 10 logଵ൬ߝߨ32େ୳ߪ
൰+ 10 logଵቆଵߤ
ଵߪቇ= minus16814 + 10 logଵቆ
ଵߤ
ଵߪቇ
The absorption term can be written
ሬୟୠୱ = = eఈభభe୨ఉభభ
where
minus௭ଵߚ ௭ଵߙ = ඥߤƸଵߝƸଵ = ඥߤଵ(ߝଵminus ଵߪ frasl ) asymp (1 minus )ටଵߪଵߤ
2=1 minus
ୱଵߜ
and the skin depth is
ୱଵߜ = ඨ2
ଵߪଵߤ= ඨ
1
ߨଵߪଵߤ=
1
ඥߤߨߪେ୳
1
ඥߤଵߪଵ
Hence
௭ଵߚ asymp ௭ଵߙ asymp1
ୱଵߜ
and
ሬୟୠୱasymp eభ ఋ౩భfrasl e୨భ ఋ౩భfrasl
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 16 10 July 2015
or taking the magnitude in decibels [Paul1992 eqn (1132)]
ሬୟୠୱ [dB] = minus20 logଵ(e)
ଵ
ୱଵߜ= minus20 logଵ(e)ඥߤߨߪେ୳ ଵඥߤଵߪଵ= minus13143 ଵඥߤଵߪଵ
The multiple reflection terms is
ሬ୫ ୳୪୲୧=
1
1 minus Ԧଵߩଶ ଶ
=1
1 minus ൬minusߟ 1ߟ + 1
൰ଶ
eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
asymp1
1 minus eଶభ ఋ౩భfrasl eଶ୨భ ఋ౩భfrasl
For thick samples ( ଵ≫ (ୱଵߜ we see that ሬ୫ ୳୪୲୧rarr 1 For thin conducting samples
ሬ୫ ୳୪୲୧rarr
1
1 minus (1 minus 2 (ଵߜ=
1
2 ଵߜ=
ୱଵߜ
2(+ 1) ଵ=
1
ඥߤߨߪେ୳
1
2(+ 1) ଵ
1
ඥߤଵߪଵ
หሬ୫ ୳୪୲୧ห[dB] = minus3263 minus 10 logଵ൫ߤଵߪଵ ଵଶ൯
Note that in this limit the product
ሬ ሬ୫ ୳୪୲୧=
2
େ୳ߪߟ
1
ଵߪ ଵ
is independent of frequency and determines the DC transmission through the sample
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus20077 minus 20 logଵ൫ߪଵ ଵ൯= minus4550 minus 20 logଵ(ߪଵ ଵ)
This can also be written as
หሬ ሬ୫ ୳୪୲୧ห[dB] = minus4550 + 20 logଵ൫ ୗଵ൯
where the surface resistance of the sample is
ୗଵ =1
ଵߪ ଵ
ldquoohms per squarerdquo This follows from the fact that the resistance across the ends of a thin film of
thickness ଵ width and lengthܮ is
=ܮଵߩ
ܣ=
ܮ
ଵߪ ଵ=
1
ଵߪ ଵ
ܮ
= ୗଵ
ܮ
ୀௐሱ⎯ሮ ୗଵ
The corresponding shielding effectiveness defined here as the reciprocal of the magnitude of the
transmission coefficient
SE [dB] = 4550 minus 20 logଵ൫ ୗଵ൯
is shown in Figure 3
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
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University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
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University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 17 10 July 2015
Figure 3 DC shielding effectiveness of a thin conductive sample as a function of its surface resistance
27 Parameter extraction methods
The complex permittivity and permeability of a material can be determined from a measurement of
its complex reflection and transmission coefficient in a TEM or TETM wave measurement cell In
this section we review these techniques and present MATLAB implementations of the most
promising ones
271 Nicholson-Ross-Weir parameter extraction
The reflection and transmission coefficient of a slab in a TEM wave and TETM waveguide structure
can both be written
Γ =Ԧଵߩ + Ԧଶeଶ୨ఋభߩ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
ሬ=Ԧଵ Ԧଶe୨ఋభ
1 + Ԧଶeଶ୨ఋభߩԦଵߩ
where the complex phase shift in the slab is
ଵߜ = ௭ଵ ଵ
For TEM waves
௭ୟ = ඥߤୟߝୟඥ1 minus (sinߠୟ)ଶఏୀሱ⎯⎯ሮ ඥߤୟߝୟ = ୟ
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (sinߠୟ)ଶ
ఏୀሱ⎯⎯ሮ ෝଵඥߤୟߝୟ = ෝଵ ୟ
while for TETM waves in a waveguide
௭ୟ = ඥߤୟߝୟඥ1 minus (ୡ frasl )ଶ =ߨ2
ୟߣඥ1 minus ୟߣ) fraslୡߣ )ଶ ≝
ߨ2
ୟߣ
0
20
40
60
80
100
120
0001 001 01 1 10
Sh
ield
ing
Eff
ec
tiv
en
es
s(d
B)
Surface Resistance (ohms per square)
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
University of York 22 10 July 2015
For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
University of York 27 10 July 2015
This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 18 10 July 2015
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ ≝ߨ2
ଵߣ
Here the guided wavelengths are
ୟߣ =ୟߣ
ඥ1 minus ୟߣ) fraslୡߣ )ଶ
ଵߣ =ୟߣ
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
In the latter case the dispersion relation includes the effects of both the complex material
parameters and the dispersion characteristics of the waves For both types of wave the transverse
impedances are given by
ߟ =
Ƹߤ
௭
ߟ =
௭
Ƹߝ
and the interfacial reflection coefficients at the two interfaces are
Ԧଵߩ =minusଵߟ ୟߟ
ଵߟ + ୟߟ
Ԧଶߩ =minusୠߟ ଵߟ
ୠߟ + ଵߟ
Since the medium on both sides is the same we find that
Ԧଵߩ = Ԧଶߩminus
Ԧଵ = 1 + Ԧଵߩ
Ԧଶ = 1 + Ԧଶߩ = 1 minus Ԧଵߩ
and the coefficients can be written
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where the transmission factor through the slab is
≝ e୨ఋభ
and the relative transverse impedance is
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
University of York 22 10 July 2015
For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
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=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
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ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
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=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
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6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 19 10 July 2015
≝ߟଵߟ
ߟ
Noting that
Ԧଵߩ =minusߟ 1
ߟ + 1hArr ߟ =
1 + Ԧଵߩ
1 minus Ԧଵߩ
minusߟ1
ߟ=
Ԧଵߩ2ଶ
1 minus Ԧଵߩଶ
these can also be written
Γ = Γ =൫ߟ
ଶ minus 1൯(1 minus ଶ)
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
ሬ= ሬ=ߟ4
൫ߟ+ 1൯ଶminus ൫ߟminus 1൯
ଶଶ
and the ratio is given by
Γ
ሬ=
Ԧଵߩ2
1 minus Ԧଵߩଶ
1 minus ଶ
2=ߟଶ minus 1
ߟ2∙1 minus ଶ
2=
1
2ቆߟminus
1
ߟቇ1 minus ଶ
2
From the definition of we can also obtain the relationships
1 + ଶ
2= cosߜଵ
1 minus ଶ
2= j sinߜଵ
j tanߜଵ =1 minus ଶ
1 + ଶ
j tanଵߜ2
=1 minus
1 +
The reflection and transmission parameters can thus also be written [Barr2012]
Γ =൫ߟ
ଶ minus 1൯j sinߜଵ
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
ሬ=ߟ2
൫ߟ+ 1൯ଶ
j sinߜଵ + eߟ2୨ఋభ
The NRW method inverts these equations directly [Nico1970Weir1974] We start by defining
ଵ≝ ሬ+ Γ
ଶ≝ ሬminus Γ
Electromagnetic properties of nanostructured materials
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so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
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Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
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For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
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log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
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୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
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=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
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Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
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det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 20 10 July 2015
so that
ଵ ଶ = ൫ሬ+ Γ൯൫ሬminus Γ൯= ሬଶminus Γଶ
ଵ+ ଶ = 2 ሬ
ଵminus ଶ = 2Γ
Factorising the combinations
ଵ ଶfrasl = ሬplusmn Γ =൫ minus Ԧଵߩ
ଶ ൯plusmn ൫ߩԦଵminus Ԧଵߩଶ൯
1 minus Ԧଵߩଶ ଶ
=൫1 ∓ Ԧଵ൯൫ߩ plusmn Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ
we obtain
ଵ = + Ԧଵߩ
1 + Ԧଵߩ
ଶ = minus Ԧଵߩ
1 minus Ԧଵߩ
and hence inverting the first relation for and the second for Ԧଵweߩ find
=ଵminus Ԧଵߩ
1 minus Ԧଵߩ ଵ=
൫ሬ+ Γ൯minus Ԧଵߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Ԧଵߩ = minus ଶ
1 minus ଶ=
minus ൫ሬminus Γ൯
1 minus ൫ሬminus Γ൯
Further considering the product
ଵ ଶ = ሬଶminus Γଶ =൫ + Ԧଵ൯൫ߩ minus Ԧଵ൯ߩ
൫1 minus Ԧଵ൯൫1ߩ + Ԧଵ൯ߩ=
ଶminus Ԧଵߩଶ
1 minus Ԧଵߩଶ ଶ
we can construct the term
൫1 minus Ԧଵߩଶ ଶ൯൛1 plusmn ൫ሬଶminus Γଶ൯ൟ= 1 minus Ԧଵߩ
ଶ ଶ plusmn ൫ ଶminus Ԧଵߩଶ ൯= ൫1 ∓ Ԧଵߩ
ଶ ൯(1 plusmn ଶ)
Defining
χ ≝1 + ଵ ଶ
ଵ + ଶ=
1 + ൫ሬଶminus Γଶ൯
2 ሬ
Υ ≝1 minus ଵ ଶ
ଵminus ଶ=1 minus ൫ሬଶminus Γଶ൯
2Γ
we can deduce
χ =1 + ൫ሬଶminus Γଶ൯
2 ሬ=൫1 minus Ԧଵߩ
ଶ ൯(1 + ଶ)
2൫1 minus Ԧଵߩଶ ൯
=1 + ଶ
2
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
University of York 22 10 July 2015
For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
University of York 27 10 July 2015
This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 21 10 July 2015
Υ =1 minus ൫ሬଶminus Γଶ൯
2Γ=൫1 + Ԧଵߩ
ଶ ൯(1 minus ଶ)
Ԧଵ(1ߩ2 minus ଶ)=
1 + Ԧଵߩଶ
Ԧଵߩ2
These quadratic equations can be solved to give
= χ plusmn ඥχଶminus 1 with || le 1
Ԧଵߩ = Υplusmn ඥΥଶminus 1 withหߩԦଵหle 1
where the signs are chosen to maintain a modulus less than or equal to unity Note that
Υ plusmn 1 =൫1 plusmn Ԧଵߩ
ଶ ൯ଶ
ሬሬሬሬଵߩ2ଶ
It is also possible to determine the relative transverse impedance and propagation factor directly in
terms of the scattering parameters [Ziol2003]
ߟଶ =
Υ + 1
Υ minus 1=
1 + ଵ
1 minus ଵ∙1 minus ଶ
1 + ଶ=൫Γ + 1൯
ଶminus ሬଶ
൫Γ minus 1൯ଶminus ሬଶ
with Re le൧ߟ 0
= e୨ఋభ = cosߜଵminus j sinߜଵ =1 + ଶ
2minus1 minus ଶ
2=
1 + ሬଶminus Γଶ
2 ሬminus
2Γ
൫ߟminus 1 fraslߟ ൯ሬ
Direct inversion then proceeds from the transmission factor through the slab
e୨ఋభ = e୨భభ =
by taking the logarithm of both sides
minusj ௭ଵ ଵ = log()
allowing the complex wave vector to be obtained as
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
The complex logarithm has multiple branches corresponding to the thickness of the slab being
multiples of the wavelength in the slab ଵߣ Since ଵߣ is a-priori unknown since the material
parameters are unknown this causes an ambiguity in determining the phase of the wave number
that has to be resolved as discussed below From the dispersion relation we have
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ =
ߨ2
ୟߣට ෝଵ
ଶminus ୟߣ) fraslୡߣ )ଶ =j
ଵlog()
and hence the relative complex refractive index is determined as
ෝଵଶ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
=1
ୟଶ൬
j
ଵlog()൰
ଶ
+ ቀୡቁଶ
Electromagnetic properties of nanostructured materials
University of York 22 10 July 2015
For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 22 10 July 2015
For non-magnetic materials we can assume Ƹଵߤ = 1 and obtain the relative permittivity as
Ƹଵߝ =Ƹଵߝୟߝ
=ƸୟߤƸଵߤ
ෝଵଶ
ఓෝ౨భୀଵሱ⎯⎯⎯ሮ ෝଵ
ଶ
In the general case the permeability can be obtained from the relative transverse impedance (for
TEMTE waves only) using
ߟ =ଵߟ
ߟ=ƸଵߤƸୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
ଵߣ
ୟߣ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
giving
Ƹଵߤ =ƸଵߤƸୟߤ
=ୟߣ
ଵߣቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ=
ඥ ෝଵଶminus ୟߣ) fraslୡߣ )ଶ
ඥ1 minus ୟߣ) fraslୡߣ )ଶቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
The permittivity then follows either from the relative refractive index
Ƹଵߝ =Ƹଵߝୟߝ
=ෝଵଶ
Ƹଵߤ
or by inverting the dispersion relation
ෝଵଶ = ƸଵߝƸଵߤ = ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
= ቆୟߣଵߣ
ቇ
ଶ
+ ൬ୟߣୡߣ൰ଶ
to give
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߣଶ
Ƹଵߤቆ
1
ଵߣଶ +
1
ୡߣଶቇ
This can also be written
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ= ඥ1 minus (ୡ frasl )ଶƸୟߤƸଵߤቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ൬
௭ଵ
ୟ൰+
ƸୟߤƸଵߤቀୡቁଶ
The complex wave number
௭ଵ =ߨ2
ଵߣ=
j
ଵlog()
is a multi-valued complex function Writing
= ||e୨థe୨ଶగ with minus geߨ lt ߨ
we define the principal value of the logarithm by
Log() ≝ log|| + j
so that the branches are given explicitly by
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
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This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
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The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
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Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 23 10 July 2015
log() = Log() + j2ߨ= log|| + j( + (ߨ2
where ni ℤ and = 0 for the principal branch (this is compatible with MATLAB) Hence
௭ଵ =ߨ2
ଵߣ=
j
ଵlog() =
j
ଵlog|| minus
+ ߨ2
ଵ
The phase constant is
௭ଵߚ = Re ௭ଵ൧=ߨ2
Re ଵ൧ߣ= minus
+ ߨ2
ଵ
so the electrical length of the slab is
ଵ
Re ଵ൧ߣ=
ଵߚ௭ଵ
ߨ2= minus
+ ߨ2
ߨ2= minus
ߨ2
minus
For the principal branch = 0 and we find that geߨminus le 0 corresponds to ଵ le Re ଵ൧ߣ 2frasl At
low enough frequency we therefore expect to be in the principal branch however at higher
frequencies gt 0 corresponding to the slab being multiple wavelengths thick
One way to resolve the branch ambiguity is to use a stepwise approach to determine the phase at
each frequency point ൛= 1 hellip ൟfrom that at the last frequency point assuming that the first
frequency in the series lies in the principal branch ଵ le Re ଵ൧ߣ 2frasl and that the interval between all
the frequency points is such that ൫ ൯minus ൫ ଵ൯lt ߨ [Luuk2011] For the first frequency we
calculate
( ଵ) = arg[( ଵ)] s t geߨminus ( ଵ) le 0
௭ଵ( ଵ) ଵ = j log|( ଵ)| minus ( ଵ)
and then for successive frequencies we calculate
൫ ൯= ൫ ଵ൯+ argቈ൫ ൯
൫ ଵ൯= ( ଵ) + argቈ
( )
( ଵ)
ୀଵ
(gt 1)
so that
௭ଵ൫ ൯ଵ = j logห ൫ ൯หminus ( ଵ) minus argቈ( )
( ଵ)
ୀଵ
(gt 1)
This is equivalent to unwrapping the phase of the principal argument of log() [Barr2012] Note
that phase unwrapping has the same requirements the lowest frequency should be in the principal
(p=0) branch and ൫ ൯minus ൫ ଵ൯lt ߨ
Another way to deal with the ambiguity is to measure the group delay ୫ through the slab
[Weir1974Chal2009]
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
University of York 27 10 July 2015
This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 24 10 July 2015
୫ ୟୱ= minus1
ߨ2
d୫ ୟୱ
d= ଵ
dߚ௭ଵ
d=
ଵ
ߨ2
dߚ௭ଵ
d
and compare it to the group delay predicted by the algorithm
௭ଵߚ =ߨ2
ଵ ୫ ୟୱ= minus
+ ߨ2
ଵ
to give
= minusߨ2
minus ୫ ୟୱ
= roundminusߨ2
minus ୫ ୟୱ൨= roundቈminusIm[Log()]
ߨ2minus ୫ ୟୱ
We round to the nearest integer since minus2) ߨ(1 le le +2) ߨ(1 corresponds to minus2minus)
1) Re ଵ൧ߣ 2frasl le ଵ le +2minus) 1) Re ଵ൧ߣ 2frasl
For TEM waves the dispersion relations reduce to [Ghod1989Ghod1990]
௭ୟ = ඥߤୟߝୟ
௭ଵ = ඥߤୟߝୟෝଵ = ඥߤୟߝୟඥߤƸଵߝƸଵ
Once the wave number and transverse interfacial reflection coefficient have been found from the
inversion above the material parameters can be obtained via the relative impedance
ߟ = ඨƸଵߤ
Ƹଵߝ=
1 + Ԧଵߩ
1 minus Ԧଵߩ
using
Ƹଵߝ =ෝଵߟ
=௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ = ෝଵߟ =௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
272 Thin slab limit
For thin slabs the transmission factor can be approximated to first order using [Ziol2003]
1 minus = 1 minus e୨ఋభ భభ൧≪ଵሱ⎯⎯⎯⎯⎯⎯⎯⎯ሮ 1 minus (1 minus jߜଵ) = jߜଵ = j ௭ଵ ଵ
Hence
1 minus asymp j ௭ଵ ଵ =൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
University of York 27 10 July 2015
This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 25 10 July 2015
=ߟ1 +
1 minus ∙1 minus ሬ+ Γ
1 + ሬminus Γasymp
2
j ௭ଵ ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
can be reduced to
௭ଵ =1
j ଵ
൫1 minus ሬminus Γ൯൫1 + Ԧଵ൯ߩ
1 minus +Ԧଵ൫ሬߩ Γ൯
ߟ ௭ଵ =2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ
In the first equation the interfacial reflection coefficient determined from the NRW inversion or
directly from the scattering parameters can be used to determine the wave number without any
issues related to the logarithm But it seems to give a relatively inaccurate result for ௭ଵ For TEM
and TE waves
ߟ ௭ଵ =ଵߟ ௭ଵ
ୟߟ=Ƹଵߤୟߟ
hence
Ƹଵߤ =ୟߟ2
j ଵ∙1 minus ሬ+ Γ
1 + ሬminus Γ=
ୟߟ2j ଵ
1
ඥ1 minus (ୡ frasl )ଶ∙1 minus ሬ+ Γ
1 + ሬminus Γ
Now
ߟ =ଵߟ
ୟߟ=Ƹଵߤୟߤ
௭ୟ
௭ଵ= Ƹଵߤ
௭ୟ
௭ଵ=
ඥ1 minus (ୡ frasl )ଶ
ඥ ෝଵଶminus (ୡ frasl )ଶ
so
ෝଵଶ = ƸଵߝƸଵߤ = ቆ
Ƹଵߤ
ߟቇ
ଶ
൬1 minus ቀୡቁଶ
൰+ ቀୡቁଶ
Using the equation for the relative impedance gives
Ƹଵߝ =Ƹଵߤ
ߟଶ ൬1 minus ቀ
ୡቁଶ
൰+1
Ƹଵߤቀୡቁଶ
ఠౙrarrሱ⎯⎯ሮ
Ƹଵߤ
ߟଶ =
ୟߟ2
j ଵ∙1 minus ଵ
1 + ଵ
Alternatively from the dispersion relation
Ƹଵߝ =Ƹଵߝୟߝ
=1
Ƹଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ=ୟߤƸଵߤቊ൬
௭ଵ
ୟ൰ଶ
+ ቀୡቁଶ
ቋ
These equations can also be derived by considering
Vଵminus 1
Vଵ + 1=ሬ+ Γ minus 1
ሬ+ Γ + 1=
minusj
ߟtan
ଵߜ2asymp minusj
ଵ
2௭ଵ
ߟ= minusj
ଵ
2
ୟߟ ௭ଵ
ଵߟ
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
University of York 27 10 July 2015
This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 26 10 July 2015
Vଶminus 1
Vଶ + 1=ሬminus Γ minus 1
ሬminus Γ + 1= minusjߟtan
ଵߜ2asymp minusj
ଵ
2ߟ ௭ଵ = minusj
ଵ
2
Ƹଵߤୟߟ
The second equation is the same as the one above and allows the permeability to be determined
The permittivity can then be determined from the dispersion relation as above or the first equation
can be used to determine
௭ଵ
ଵߟ=
௭ଵଶ
Ƹଵߤ=ୟߝୟߤƸଵߤ
൜ෝଵଶminus ቀ
ୡቁଶ
ൠ
and thus
ෝଵଶ =
ƸଵߝƸଵߤୟߝୟߤ
=Ƹଵߤ
ୟߝୟߤ
௭ଵ
ଵߟ+ ቀ
ୡቁଶ
giving
Ƹଵߝୟߝ
=1
ୟߝቆ
௭ଵ
ଵߟቇ+
ୟߤƸଵߤቀୡቁଶ
For TEM waves the permittivity and permeability can both be obtained directly since
ୟߟ ௭ଵ
ଵߟ=ୟߝୟߤୟߟ
Ƹଵߤ
( ෝଵଶminus (ୡ frasl )ଶ)
ඥ1 minus (ୡ frasl )ଶ ఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߝୟߝ
Ƹଵߤୟߟ
=Ƹଵߤୟߟ
ඥ1 minus (ୡ frasl )ଶఠౙrarrሱ⎯⎯ሮ ୟ
Ƹଵߤୟߤ
giving
Ƹଵߝୟߝasymp
2j
ୟ ଵ∙ሬ+ Γ minus 1
ሬ+ Γ + 1
Ƹଵߤୟߤ
asymp2j
ୟ ଵ∙ሬminus Γ minus 1
ሬminus Γ + 1
These equations do not require any of the NRW inversion variables and can be evaluated directly
However the permeability equation may not be as well behaved as the permittivity equation since it
contains the 1 plusmn ଵ terms [Ziol2003]
273 The effective parameter method
We define the effective relative permittivity and permeability such that
௭ଵ ≝ ௭ୟඥߤƸଵߝƸଵ
≝ߟ ඨƸଵߤƸଵߝ
Electromagnetic properties of nanostructured materials
University of York 27 10 July 2015
This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 27 10 July 2015
This is valid for quasi-TEM structures ndash such as microstrip and stripline - as well true TEM lines We
can also reformulate waveguide using effective parameters The wave number can be written
௭ଵ = ඥߤୟߝୟට ෝଵଶminus (ୡ frasl )ଶ ≝ ௭ୟඥߤƸଵߝƸଵ
by taking
Ƹଵߤ = Ƹଵߤ
Ƹଵߝ = ൬1 minus ቀୡቁଶ
൰ߝƸଵ +1
Ƹଵߤቀୡቁଶ
The effective parameter problem is isomorphic to TEM problem The solution is straightforward
once the wave numbers in the two regions and the relative impedance are known [Boug1997]
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ
Ƹଵߤ =௭ଵ
௭ୟߟ
We can therefore determine effective parameters from the wave number and wave impedance (or
interfacial reflection coefficient) from an NRW inversion
Ƹଵߝ =௭ଵ
௭ୟ
1
ߟ=
௭ଵ
௭ୟቆ1 minus Ԧଵߩ
1 + Ԧଵߩቇ
Ƹଵߤ =௭ଵ
௭ୟ=ߟ
௭ଵ
௭ୟቆ
1 + Ԧଵߩ
1 minus Ԧଵߩቇ
As usual
ƸଵߤƸଵߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଶ
ෝ ଵ = ƸଵߝƸଵߤ = ቆ௭ଵ
௭ୟቇ
ଶ
If the material is non-magnetic with Ƹଵߤ = 1 then
Ƹଵߝ = Ƹଵ൯ߤƸଵ൫ߝ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ୟߣ
௭ଵߣቇ
ାଵ
= ቆ1 + Ԧଵߩ
1 minus Ԧଵߩቇ
ଵ
ቆ௭ଵ
௭ୟቇ
ାଵ
where isin ℝ A number of choice for n have been made in the literature
n = -1 Stuchly [Stuc1978]
n = 0 NRW [Nich1970]
n = 1 Boughriet non-iterative method [Boug1997]
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 28 10 July 2015
The choice n = 1 is numerically more robust as it eliminates the problematic 1 minus Ԧଵߩ 1 + fraslԦଵߩ
terms however it does not help for magnetic materials
274 Sample position and thickness independent methods
The scattering parameters at the reference planes of the material are
Γ = Γ = Ԧଵߩ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= Ԧଵߩ
1 minus ଶ
1 minus Ԧଵߩଶ ଶ
ሬ= ሬ=൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
=൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
The scattering parameters measured by a VNA including sections of assumed lossless propagation
of length ୟୠon each port are
ଵଵ ଵଶ
ଶଵ ଶଶ൨= Γeଶ୨ఋ ሬe୨(ఋାఋౘ)
ሬe୨(ఋାఋౘ) Γeଶ୨ఋౘ൨
where
ୟߜ = ௭ୟ ୟ
ୠߜ = ௭ୠ ୠ = ௭ୟ ୠ
Explicitly these give
ଵଵ = eଶ୨ఋߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଵଶ = ଶଵ = e୨(ఋାఋౘ)൫1 minus Ԧଵߩ
ଶ ൯e୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
ଶଶ = eଶ୨ఋౘߩԦଵ
1 minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
Uncertainty in ୟୠcan be a significant cause of error The alleviate this we can form various
combinations of the scattering parameters that are independent of the position of the sample in
line We assume that the total length of the measurement system is
= ୟ + ଵ + ୠ
and that the length of the sample is also known accurately Hence
minus ଵ = ୟ + ୠ
is known but not the individual lengths ୟ and ୠ Invariant combinations include [Bake1990
Chal2009]
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 29 10 July 2015
det= ଵଵ ଶଶminus ଵଶ ଶଵ = eଶ୨( భ)Ԧଵߩଶ minus eଶ୨ఋభ
1 minus Ԧଵߩଶ eଶ୨ఋభ
= eଶ୨( భ)Ԧଵߩଶ minus ଶ
1 minus Ԧଵߩଶ ଶ
≝ minuseଶ୨( భ)ܤ
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ܣ =ଵଵ ଶଶ
ଵଶ ଶଵ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
൫1 minus eଶ୨ఋభ൯ଶ
eଶ୨ఋభ=
Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ
=ଵଶ + ଶଵ
ଵଶ + ଶଵ
= e୨భ൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
where
ଵଶ = ଶଵ
= e୨
is the transmission factor through the empty cell We deduce that
ܤ =ଶminus Ԧଵߩ
ଶ
1 minus Ԧଵߩଶ ଶ
rArr ଶ =ܤ + Ԧଵߩ
ଶ
1 + Ԧଵߩܤଶ
rArr ܣ =Ԧଵߩଶ
൫1 minus Ԧଵߩଶ ൯
ଶ
(1 minus ଶ)ଶ
ଶ=
Ԧଵߩଶ (1 minus ଶ(ܤ
൫ܤ + Ԧଵߩଶ ൯൫1 + Ԧଵߩܤ
ଶ ൯
This can be rearranged into a quadratic equation for Ԧଵߩଶ and solved to give
Ԧଵߩଶ =
1)ܣminus + (ଶܤ + (1 minus ଶ(ܤ
ܤܣ2= plusmn
ඥminus4ܣଶܤଶ + 1)ܣ + (ଶܤ minus (1 minus ଶଶ(ܤ
ܤܣ2
We choose the sign so that หߩԦଵหle 1 The remaining ambiguity from taking the square root must be
resolved by using the techniques above
275 NIST iterative inversion
NIST have developed a robust inversion method based on the equations [Bake1990]
ଵଶ + ଶଵ
2= e୨( భ)
൫1 minus Ԧଵߩଶ ൯
1 minus Ԧଵߩଶ ଶ
ଵଵ + ଶଶ
2=
eଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
They use an iterative solver to find the solution of the non-linear equations
ܠ)۴ ω β) =
where
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 30 10 July 2015
=ܠ ߝᇱ
ߝᇱᇱ൨
ܠ)۴ ω β) = ܠ)ܨ ω β)ܠ)୧ܨ ω β)
൨
ܠ)୧ܨ ω β) = Re Imfrasl ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
൩
The solution is found independently at each frequency point The NRW inversion can be used to
provide an initial guess is varied according to the sample length measurement noise and material
For low loss materials the transmission is strong so we take = 0
For high loss materials the reflection is strong so we take to be large
Generally we take as a ratio of noiseuncertainty in S21 to that in S11
The solution can be achieved using a multivariate Newton-Rhapson approach [Bake1990AppE ]
ܠ = minusଵܠ (ଵܠ)۴(ଵܠ)۸
where the Jacobian matrix is
(ܠ)۸ = ൦
part ଵ fraslଵݔpart part ଵ fraslଶݔpart
part ଶ fraslଵݔpart part ଶ fraslଵݔpart⋯ part ଵ fraslݔpart
hellip part ଶ fraslݔpart⋮ ⋮
part fraslଵݔpart part fraslଵݔpart⋱ ⋮hellip part fraslݔpart
൪ተ
ܠ
or another nonlinear equation solver The Jacobian can be evaluated using finite difference
approximations in order to obtain a derivative-free problem
Note that the second term is not reference plane invariant For an invariant approach we can use
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ det
or
ߚଵଶ + ଶଵ
2+ (1 minus (ߚ
| ଵଵ| + | ଶଶ|
2
instead We can generalise this to obtain the permeability by adding a second complex equation The
approach can also be restated as an optimisation problem
minܠ
ܠ) ω β)
where
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 31 10 July 2015
ܠ) ω β) = อ൬ଵଶ + ଶଵ
2+ ߚ
ଵଵ + ଶଶ
2൰ฬ୫ ୟୱ
minus ቆe୨( భ)൫1 minus Ԧଵߩ
ଶ ൯
1 minus Ԧଵߩଶ ଶ
+ ߚeଶ୨ + eଶ୨ౘ
2∙Ԧଵ(1ߩ minus ଶ)
1 minus Ԧଵߩଶ ଶ
ቇቤܠ
อ
ଶ
[Bart2010] fitted the calculated ଵଵ ଵଶ with a polynomial approximation
ߝᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱ()
ே
ୀ
ߝᇱᇱ() =
ே
ୀ
= prod ൫ minus ൯ேୀଵஷ
prod ൫ minus ൯ேୀଵ
ߝᇱᇱ()
ே
ୀ
of the permittivitypermeability to the measured values This uses the Lagrange representation of
the polynomials in terms of functional pairs ൫ ߝᇱ()൯ with linearly spaced frequencies The
order of polynomial is increased until the prescribed error bound is met The bound is informed by
the measurement uncertainty to limit the polynomial order and avoid ldquofitting to noiserdquo
=ܠ ൦
ߝᇱ()⋮
ߝᇱᇱ()
⋮
൪
ଶேtimesଵ
൦
1⋮0⋮
൪le geܠ
maxߝ
⋮maxߝ
⋮
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
୫ ୧୬ gt ୫ ୟୱrArr rarr + 1
This gives smooth results with some immunity to noise and systematic effects but does not enforce
physical constraints on the extracted permittivity
Another approach is to enforce a prescribed model for permittivitypermeability and use an
optimisation approach This can directly enforce physical constraints but it requires prior knowledge
of likely form of material parameters [Tric2009][Zhan2010] For example a one term Debye
relaxation with DC conductivity
()Ƹߝ = ஶߝ + ߝ∆
1 + j
+ୈେߪjε
can be fitted using the GA schema
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 32 10 July 2015
=ܠ ൦
infinߝߝ∆DCߪ
൪
൦
1000
൪le geܠ ൦
maxߝmaxߝ ݔ
maxߪ
൪
ܠ) β) =1
ቤ൬ߚ
ଵଶ + ଶଵ
2+ (1 minus (ߚ det ൰ฬ
୫ ୟୱఠೖ
minus ൬ߚଵଶ + ଶଵ
2minus (1 minus (ߚ det ൰ฬ
ୡୟ୪ୡఠೖ
ቤ
ଶே
ୀଵ
minܠ
ܠ) β)
Many variations on the objective function are possible
276 MATLAB implementation and experiment simulation
1 A number of the extraction algorithms reviewed above have been implemented in the AEG
MATLAB Materials Toolbox The functions are summarized in Table 2
Function Description
matExtractNRW Basic NRW algorithm
matExtractNRWThin NRW algorithm with thin-sheet assumption
matExtractEffective Effective parameter algorithm
matExtractNIST NIST iterative algorithm
matExtractGA GA based optimization algorithm
matTestExtract Test function implementing simulated measurement with errors
Table 2 Parameter extraction functions implemented in the AEG Materials Toolbox
In addition to the extraction functions themselves a test function that implements a simulated
measurement was also developed In outline this function carries out the following steps
1 A set of known material parameters (relative permittivity permeability and thickness are
taken as inputs
2 The scattering parameters of the planar material slab referenced to the surfaces of the
sample are determined using a multilayer transmission and reflection code
3 The reference planes are moved to the locations of the two ports of a test cell of prescribed
geometry
4 Gaussian noise is added to the scattering parameters to give a defined signal-to-noise ratio
(SNR)
5 Systematic errors are introduced into the locations of the reference plane and sample
thickness according to a specified relative error
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 33 10 July 2015
6 Each of the extraction algorithms is then applied to the simulated measured scattering
parameters to determine the relative permittivity and permeability
The extracted parameters are finally compared to the known input parameters
The results from a simple example consisting of a 5 mm thick slab of non-magnetic material with a
frequency independent relative permittivity of 4 and conductivity of 01 Sm are shown in Figure 4
In this case the SNR was set at 50 dB and no systematic errors were introduced For this simple low
permittivity material all the algorithms are fairly reliable however the direct inversion algorithms
show significant errors at some frequencies due to the noise on the simulated measurement data
The indirect algorithms are much less susceptible to the simulated measurement noise
Another more realistic example is shown in Figure 5 In this case the input material parameters are a
parametric model for the permittivity of infiltrated fat derived from experimental data [Gabr1996]
The SNR was again set at 50 dB and a 1 systematic error in the sample location in the cell was
introduced The direct inversion algorithms are seen to be particularly sensitive to systematic errors
while the indirect methods are generally more reliable
3 A coaxial measurement jig
In order to measure the shielding effectiveness of a sheet material it is necessary to illuminate it on
one side with an electromagnetic wave and measure how much of the wave passes through the
material to the other side The main problems are
Preventing any energy passing around the edges of the sample
Ensuring that unwanted standing waves are not excited as they will affect the frequency
response of the system
The solution chosen here is to incorporate the sample sheet into a coaxial transmission line Given
the difficulty in fabricating large samples of new materials incorporating nano-particles it is also
desirable that the sample be as small as possible A small sample size helps with preventing
unwanted standing waves However the sample must be large enough to allow easy handling of the
jig and sample and for the jig to be manufactured by the Physics and Electronics mechanical
workshops Also it must be possible to attach the jig to a suitable RF cable by means of a standard
connector suitable for 20 GHz operation
31 Design of a coaxial measurement jig
Due to the difficulty of manufacturing a suitable connector adaptor an SMA female-female adaptor
was chosen as the basis for the jig to cable interface and is shown in yellow on the right hand side of
Figure 6 A sample diameter of about 40 mm was small enough to be manufactured and an inner
diameter for the central conductor of 10 mm was chosen as viable for manufacture (orange in Figure
6) which results in a 23 mm diameter for the inside of the outer conductor in order to achieve a
50 ohm characteristic impedance for the jig A 10 mm wide flange was chosen resulting in an overall
outside diameter at the flange of 43 mm The flange size is sufficient to allow for 3 mm bolts to hold
the two halves of the jig together
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 34 10 July 2015
Figure 4 Extracted parameters for a 5mm thick slab of material with r = 4 and = 01 Sm The results for the directinversion algorithms are shown at the top and those for the indirect algorithms at the bottom
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 35 10 July 2015
Figure 5 Extracted parameters for a 5mm thick slab of infiltrated fat using a parametric model for the complexpermittivity The results for the direct inversion algorithms are shown at the top and those for the indirect algorithms atthe bottom
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 36 10 July 2015
Figure 6 Cross sectional CAD view of one half of jig
Figure 7 3D views of jig CAD
The conductors must be tapered down to meet the SMA adaptor and as the SMA adaptor has a
PTFE dielectric a tapered PTFE insulator can be used to locate the central conductor (grey in Figure
6) A suitable curve must be computed to ensure that a 50 ohm impedance is maintained at the
transition from PTFE to air The outer conductor of the jig (grey in Figure 6) is made in two parts
joined by a threaded section This allows the alignment of the ends of the inner and outer
conductors to be adjusted
A stand was also manufactured to hold the jig in a vertical position during operation Figure 8 shows
a view from above of a completed jig in the stand with the top half removed A removable centre pin
was also added to the centre conductor to aid alignment and to locate the centre of the reference
sample for some measurements Brass (conducting) and nylon (non-conducting) versions of the pin
were manufactured
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 37 10 July 2015
Figure 8 Completed lower half of the jig in its stand
The fully assembled jig with a sample inserted can be seen in Figure 9 The changes in outline and
fabrication of the threads on the outer conductor can be seen
Figure 9 Completed jig in stand with connector shell attached to the top
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 38 10 July 2015
32 Coaxial jig test sample manufacture
In order to fully characterise the performance of the new coaxial measurement jig outlined in
Section 31 it was necessary to prepare a preliminary validation sample This was used to make
semi-quantitative measurements of the jigs performance and will allow the characterisation of
future materials which incorporate nanoscale structures that modify their electromagnetic response
Such materials are thought to be potentially very useful for a variety of applications including RF
absorbent materials filters and adaptive lsquosmartrsquo materials
Our validation sample consisted of a thin continuous film of copper grown under vacuum on a 50 μm
thick supporting polyamide film substrate known commercially as Kapton HN manufactured by
DuPont Kapton was chosen for the substrate because it has high thermal and mechanical stability
which is needed to support the very thin conductive copper films Kapton is also virtually transparent
to RF in this frequency range and thickness it is electrically non-conductive A thermal evaporator
was used to grow the copper film from a tungsten crucible and the thickness was monitored during
film growth by a quartz crystal microbalance as illustrated in Figure 10(a) The substrate had several
apertures to allow it to be accurately located within the measurement jig and clamped firmly in
place these can be seen in Figure 10(b) A repeatable method of sample location within the jig is
important if consistent and reproducible measurements are to be made It is also important to
clamp the sample firmly between the two halves of the jig to avoid the introduction of gaps from
which signal loss can occur during measurements
Figure 10 (a) The thermal evaporation chamber used to grow the copper thin films atop the polyamide Kaptonsubstrate The film thickness was monitored during film growth using the quartz microbalance shown in the figure (b)shows the kapton substrate including the central locating hole and surrounding clamping holes
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 39 10 July 2015
A representative (2 x 2) cm square test piece was grown at the same time as the validation film then
removed to our measurements laboratory where its sheet resistance was measured using a four-
point-probe Hall effectresistometer as seen in Figure 11(a) and (b) The film thickness and
associated sheet resistance of the validation sample were determined as 339 nm and 1303 Ω
respectively The RF validation measurement results are included in Section 33 below
Figure 11 (a) The four-point-probe resistometer used to measure the sheet resistances of the representative square testpiece for the validation sample (b) the sample holder card and gold contacts
Ultimately a range of film thicknesses will be prepared to enable a complete validation of the
coaxial measurement jig Increasingly thicker films cause greater attenuation to the test signals In
addition to the preliminary validation sample a range of relatively thick perforated brass calibration
samples were manufactured whose performance is relatively easy to describe using a predictive
mathematical model These are shown in Figure 12 Comparative measurements can be performed
when the perforated calibration samples are replaced with either the validation sample or future
test samples incorporating nanomaterials
Figure 12 Brass calibration samples
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 40 10 July 2015
33 Coaxial jig test results
The transmission through samples in the measurement jig was measured using a vector network
analyser The shielding effectiveness of a sample is the reciprocal of the transmission coefficient of
the jig with the sample present
Figure 13 Coaxial shielding test jig measurement setup
In order to test the jig performance one of the perforated plate test samples was measured as
shown in Figure 14
Figure 14 Perforated plate test sample on the open coaxial jig
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 41 10 July 2015
Preliminary tests on the original jig design showed that the mechanical stability of the threaded
sections was not adequate Figure 15 shows the results of four measurements of a perforated plate
test sample demonstrating poor measurement repeatability
Figure 15 Repeated shielding measurements of a perforated plate with 075 mm diameter holes at 25 mm pitchshowing variability due to movement of the threaded sections and connector inserts
The shielding with no sample in the jig should remain at zero decibels but as can be seen in Figure 18
there were some significant features which also exhibited a degree of variability from measurement
to measurement
Figure 16 Repeated shielding measurements of empty jig showing variability due to movement of the threadedsections and connector inserts
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 42 10 July 2015
Locking rings (see Figure 17) were manufactured for the threaded sections and connector inserts
which resulted in improved repeatability between measurements
Figure 17 Modified jig showing locking ring and connector locking tab
Figure 18 shows the results of measurements of the modified shielding with no sample in the jig The
variability has been reduced a little though there are still some significant features which warrant
further investigation
A solid brass test sample was then measured to determine the upper limit of shielding measurement
due to the network analyser sensitivity Figure 19 shows the resulting upper limit it is repeated on
other following graphs along with the empty jig results to indicate the valid measurement range
Figure 20 shows two measurements of the shielding effectiveness of the 03 mm thick perforated
plate sample with 075 mm holes on a 25 mm pitch It can be seen that where the shielding is within
the measurement limits the shape and level of the measured result corresponds to the analytic
estimate though the absolute value matches better if the hole size is set to 085 mm The brass
sample was formed by etching and the actual hole size and shape are somewhat variable A small
number of the holes were subsequently investigated using an optical microscope Figure 21 shows
images of four of the holes The hole diameter varied between 082 mm and 089 mm The
measurement can be seen to oscillate around the analytic value This is likely to be due to
imperfections in the jig causing unwanted reflections and further investigation is required
A second perforated plate with 15 mm holes at a 5 mm pitch was also fabricated as part of the jig
test set Figure 22 shows the measured shielding effectiveness for two separate measurements
compared with an analytic estimate of the shielding of the plate Again the measurement is seen to
oscillate about the analytic solution
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 43 10 July 2015
Figure 18 Repeated shielding measurements of empty jig showing reduced variability
Figure 19 Measurement of a 03 mm thick solid brass sample which shows the upper limit of shielding measurement
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Empty jig 2 no pin ferrites on cables
Empty jig 3 no pin
Empty jig 4 brass pin
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
120
Frequency (MHz)
SE
(dB
)
Solid brass sample 1 brass pin
Solid brass sample 2 no pin
Solid brass sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 44 10 July 2015
Figure 20 Shielding measurement of the perforated plate sample with 075 mm holes on a 25 mm pitch compared withan analytic estimate
Figure 21 Optical microscope images of four holes in the perforated plate sample with 075 mm holes on a 25 mmpitch Clockwise from the top left the hole diameters (verticalhorizontal) are 084088 mm 084089 mm082087 mm and 083088 mm
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
075mm hole 25mm pitch brass sample 1 brass pin
075mm hole 25mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
075mm hole 25mm pitch 03mm thick plate analytic
085mm hole 25mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 45 10 July 2015
Figure 22 Shielding measurement of the perforated plate sample with 15 mm holes on a 5 mm pitch in comparisonwith an analytic estimate
The copper coated Kapton sample described earlier is shown in Figure 23 on the open jig Figure 24
shows the measured shielding for this sample Based on the sheet resistance measurement a
shielding effectiveness of 43 dB was expected It can be seen in Figure 24 that the measured
shielding effectiveness oscillates about the expected value at frequencies between 2 and 20 GHz
Below 2 GHz the measured shielding value is approximately 40 dB which corresponds to a sheet
resistance 165 times higher than that originally measured The analytic calculations here ignore the
Kapton substrate and consider only the effect of the copper Figure 25 shows measurements of the
Kapton substrate compared with the empty jig It can be seen that with the Kapton sample present
the result is practically identical to that of the empty jig
Figure 23 339 nm copper on Kapton substrate sample on the open jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
15mm hole 5mm pitch brass sample 1 brass pin
15mm hole 5mm pitch brass sample 2 no pin
Solid brass sample 1 brass pin
15mm hole 5mm pitch 03mm thick plate analytic
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 46 10 July 2015
Figure 24 Shielding measurement of 339 nm copper on Kapton substrate in comparison with analytic estimates
Figure 25 Shielding measurement of Kapton substrate compared with empty jig
2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
20
40
60
80
100
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
339nm Cu on kapton (IGW 30115) brass pin
Solid brass sample 1 brass pin
339nm Cu Analytic from thickness
339nm Cu Analytic from sheet resistance
339nm Cu Analytic from 165x sheet resistance
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
2
4
6
8
10
12
14
16
18
Frequency (MHz)
SE
(dB
)
Empty jig 1 brass pin
Kapton sample 1 brass pin
Kapton sample 2 no pin
Kapton sample 3 no pin ferrites on cables
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 47 10 July 2015
4 Nanoparticle film and material fabrication
Nanomaterials are becoming increasingly more interesting as fillers for other structural materials in
order to manufacture composites that have very different physical properties to those of their
individual component materials Examples include self-cleaning glass paints and super strength
composites for the sports industry eg carbon nanotubes (CNTs) used in bicycle frames We expect
that nanomaterials will be useful for modifying electromagnetic properties and are especially
interested in their use as electromagnetic shielding materials The advent of 3D printers makes it
possible to print housings for electronic circuits that require electromagnetic shielding in which
nanomaterials can be incorporated during the printing process
The wavelength of shielded electromagnetic signals must be scaled to the dimensions of the
nanostructures when designing new shielding materials that exploit conductive losses For example
microwaves have a wavelength of the order of 10 -2 m much larger than any nanostructure
Electrically isolated nanostructures with dimensions less than a half wavelength can be transparent
to some useful frequencies This can be overcome by electrically connecting nanostructures to form
continuously conducting macrostructures Clearly conventional thin film technologies can achieve
this however it may also be possible to create materials with anisotropic (directional) shielding
properties by incorporating for example co-aligned CNTs as shown in Figure 26 Materials of this
kind can polarise electromagnetic radiation so that cross polarised variable filters can be devised
In order to work towards this goal we intend to process commercially acquired CNTs in order to
attach cobalt or nickel metal nanoparticles at their ends in a controlled manner The nanoparticles
have a large magnetic moment that will cause the CNTs to align magnetically end-to-end Useful
conductive shielding can be accomplished when this forms a continuous conductive path through
planar materials ie very thin flat sheets These sheets may also have a polarising effect as mention
above when the CNTs are co-aligned We will suspend CNTs in a supportive matrix so that they are
free to align with an external magnetic field This gives the opportunity to alter the polarisation
angle of the material
Figure 26 SEM images of CNTs (a) co-aligned and (b) randomly orientated
The same CNTs may also have interesting dielectric effects when they form a discontinuous film ie
are nonconductive In this case the individual CNTs develop an electric dipole which opposes the
driving signal and therefore attenuates it to some extent Again co-aligned dielectric CNTs may lead
to some degree of polarisation when they greatly attenuate the signal in only one orientation It has
been shown that an attenuation of 24 dB is possible using CoNi in single walled CNTs (SWCNTs)
which is attributed to dielectric (electronic and interfacial polarization) and magnetic (eddy current
and natural resonance) losses [Singh2015] This new material showed a microwave shielding
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 48 10 July 2015
effectiveness value greater than that required for commercial applications Consequently nano-
composites are promising microwave shielding materials in the Ku band We intend to magnetically
align functionalised CNTs in a nonconductive resin to further explore this effect
Figure 27 SEM image of a conductive graphene foam showing an open matrix of graphene flakes randomly orientated ina dimethyl siloxane composite [Chen2011]
In addition to our CNT work we will also develop quasi-continuous materials such as abutted
graphene flakes Recently a three dimensional graphene foam has been developed with an
exceptionally high electrical conductivity of sim10 S cmminus1 at an ultra-low graphene loading of sim05 wt
(sim022 vol) [Chen2011] This is shown in Figure 27 where the open foam matrix can be seen
Graphene has a large surface area but is only one atom thick the potential for weight savings
especially in aircraft is obvious In our work we will control the connectivity between each individual
flake and hope to thereby control the sheet resistance We will aim to achieve this by using a
rheological fluid to electrically couple the graphene flakes and more permanently by using metallic
atoms as conductive bridges When rheological fluids are used they can be manipulated by external
magnetic fields giving the opportunity to create smart adaptive materials for electromagnetic
absorbers
5 Conclusions and Plans for future work
51 Material characterisation capability
The work so far has allowed us to better understand the electromagnetic characterisation of
materials and the development of a coaxial test jig The coaxial test jig initial design was fabricated
(complete April 2015) and modified after initial tests The jig is capable of measuring the shielding
effectiveness of planar samples but suffers from some measurement artefacts which are believed to
be due to mechanical imperfections in the design It is planned to build a second version with
improved performance once further analysis of the current jig has been fabricated The MATLAB
software developed for material parameter extraction will aid future characterisation work
52 Application of nano-particle films
Due to the delay in jig manufacture and the remedial work to improve the mechanical stability the
production of test samples was delayed and is just about to commence Going forward we aim to
explore the anisotropic conductive and dielectric shielding of functionalised carbon based
nanostructures such as CNTs and graphene flakes when used in combination with magnetic metallic
atoms including Co and Ni We anticipate that the dielectric properties will dominate over
conductive effects in terms the shielding properties due to the effects of scale
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 49 10 July 2015
53 Proposals and collaboration
Future proposals are currently under discussion within the Physical Layer Research Group and with
interested outside parties
6 References
[Bake1990] J Baker-Jarvis ldquoTransmissionreflection and short-circuit line permittivity
measurementsrdquo NIST Technical Note 1341 National Institute of Standards and Technology Boulder
CO July 1990 URL httpwwweeelnistgovadvanced_materials_publicationsBaker-
Jarvis20TN2090pdf
[Bake2005] J Baker-Jarvis M D Janezic R F Riddle R T Johnk P Kabos C Holloway R G Geyer
and C A Grosvenor ldquoMeasuring the permittivity and permeability of lossy materials Solids liquids
metals building materials and negative-index materialsrdquo NIST Technical Note 1536 National
Institute of Standards and Technology Boulder CO 2005 URL
httpwwweeelnistgovadvanced_materials_publicationsBaker-Jarvis20TN1536pdf
[Barr2012] J J Barroso and A L de Paula ldquoRetrieval of permittivity and permeability of
homogeneous materials from scattering parametersrdquo Journal of Electromagnetic Waves and
Applications vol 24 no 11-12 pp 1563-1574 2010 DOI 101163156939310792149759
[Boug1997] A-H Boughriet C Legrand and A Chapoton ldquoNoniterative stable
transmissionreflection method for low-loss material complex permittivity determinationrdquo
Microwave Theory and Techniques IEEE Transactions on vol 45 no 1 pp 52-57 Jan 1997 DOI
10110922552032
[Chal2009] K Chalapat K Sarvala J Li and G S Paraoanu ldquoWideband reference-plane invariant
method for measuring electromagnetic parameters of materialsrdquo Microwave Theory and
Techniques IEEE Transactions on vol 57 no 9 pp 2257-2267 Sept 2009 DOI
101109TMTT20092027160
[Chen2011] Z Chen W Ren L Gao B Liu S Pei and H Cheng ldquoThree-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour depositionrdquo Nature
Materials Vol 10 June 2011 DOI 101038NMAT3001
[Gabr1996] S Gabriel R W Lau and C Gabriel ldquoThe dielectric properties of biological tissues III
Parametric models for the dielectric spectrum of tissuesrdquo Physics in Medicine and Biology vol 41
pp 2271-2293 1996 DOI 1010880031-91554111003
[Ghod1989] D K Ghodgaonkar V V Varadan and VK Varadan ldquoA free-space method for
measurement of dielectric constants and loss tangents at microwave frequenciesrdquo Instrumentation
and Measurement IEEE Transactions on vol 38 no 3 pp 789-793 Jun 1989 DOI
1011091932194
[Ghod1990] D K Ghodgaonkar V V Varadan and V K Varadan ldquoFree-space measurement of
complex permittivity and complex permeability of magnetic materials at microwave frequenciesrdquo
Instrumentation and Measurement IEEE Transactions on vol 39 no 2 pp 387-394 Apr 1990 DOI
1011091952520
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 50 10 July 2015
[Luuk2011] O Luukkonen S I Maslovski and S A Tretyakov ldquoA stepwise NicolsonndashRossndashWeir-
based material parameter extraction methodrdquo Antennas and Wireless Propagation Letters IEEE
vol 10 pp 1295-1298 2011 DOI 101109LAWP20112175897
[Nico1970] A M Nicolson and G F Ross ldquoMeasurement of the intrinsic properties of materials by
time-domain techniquesrdquo Instrumentation and Measurement IEEE Transactions on vol 19 no 4
pp 377-382 Nov 1970 DOI 10101109TIM19704313932
[Paul1992] C R Paul ldquoIntroduction to Electromagnetic Compatibilityrdquo John Wiley New York 1992
[Singh2015] B P Singh D K Saket A P Singh Santwana Pati T K Gupta V N Singh S R
Dhakate S K Dhawan R K Kotnala and R B Mathur ldquoMicrowave shielding properties of CoNi
attached to single walled carbon nanotubesrdquo J Mater Chem A May 2015 Vol 3 13203-13209
DOI 101039C5TA02381E
[Stuc1978] S Stuchly C Sibbald and J Anderson ldquoA new aperture admittance model for open-
ended waveguidesrdquo IEEE Transactions on Microwave Theory and Techniques vol 42 no 2
pp 192ndash198 Feb 1994 DOI 10110922275246
[Tric2009] S Tricarico F Bilotti and L Vegni ldquoA genetic algorithm based procedure to retrieve
effective parameters of planar metamaterial samplesrdquo Proc SPIE 7353 Metamaterials IV 73530H
12 May 2009 DOI 10111712820648
[Weir1974] W B Weir ldquoAutomatic measurement of complex dielectric constant and permeability at
microwave frequenciesrdquo Proceedings of the IEEE vol 62 no 1 pp 33- 36 Jan 1974 DOI
101109PROC19749382
[Zhan2010] J Zhang M Y Koledintseva G Antonini J L Drewniak A Orlandi and K N Rozanov
ldquoPlanar transmission line method for characterization of printed circuit board dielectricsrdquo Progress
In Electromagnetics Research (PIER) vol 102 pp 267-286 2010 URL
httpwwwjpierorgPIERpierphppaper=10012807
[Ziol2003] R W Ziolkowski ldquoDesign fabrication and testing of double negative metamaterialsrdquo
Antennas and Propagation IEEE Transactions on vol 51 no 7 pp 1516-1529 July 2003 DOI
101109TAP2003813622
7 Bibliography
[Agil85071E] Agilent 85071E ldquoMaterials measurement software Technical overviewrdquo 2012 URL
httpwwwhomeagilentcomagilentproductjspxnid=-
53690247553688326800amplc=engampcc=GB
[Agil2006] Agilent ldquoBasics of measuring the dielectric properties of materialsrdquo Agilent Technologies
Application Note 5989-2589EN 2006 URL httpcpliteratureagilentcomlitwebpdf5989-
2589ENpdf
[ASTM4935] ASTM Standard D4935-10 ldquoStandard test method for measuring the electromagnetic
shielding effectiveness of planar materialsrdquo ASTM International West Conshohocken PA June
2010 DOI 101520D4935-10
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 51 10 July 2015
[ASTMD5568] ASTM Standard D5568-08 ldquoStandard test method for measuring relative complex
permittivity and relative magnetic permeability of solid materials at microwave frequenciesrdquo ASTM
International West Conshohocken PA May 2012 DOI 101520D5568-08
[Badi2002] M Badic and M-J Marinescu ldquoThe failure of coaxial TEM cells ASTM standards methods
in HF rangerdquo Electromagnetic Compatibility 2002 EMC 2002 IEEE International Symposium on
vol 1 pp 29-34 19-23 Aug 2002 DOI 101109ISEMC20021032442
[Bake1990b] J Baker-Jarvis E J Vanzura and W A Kissick ldquoImproved technique for determining
complex permittivity with the transmissionreflection methodrdquo Microwave Theory and Techniques
IEEE Transactions on vol 38 no 8 pp 1096-1103 Aug 1990 DOI 1011092257336
[Barr2001] J J Barroso and U C Hasar ldquoUnambiguous determination of constitutive parameters of
a metamaterial slabrdquo Microwave and Optoelectronics Conference (IMOC) 2011 SBMOIEEE MTT-S
International pp 498-502 29 Oct - 1Nov 2011 DOI 101109IMOC20116169261
[Barr2012b] J J Barroso and U C Hasar ldquoConstitutive parameters of a metamaterial slab retrieved
by the phase unwrapping methodrdquo Journal of Infrared Millimeter and Terahertz Waves vol 33
no 2 pp 237-244 2012 DOI 101007s10762-011-9869-3
[Bart2010] P G Bartley and S B Begley ldquoA new technique for the determination of the complex
permittivity and permeability of materialsrdquo Instrumentation and Measurement Technology
Conference (I2MTC) 2010 IEEE pp 54-57 3-6 May 2010 DOI 101109IMTC20105488184
[Caij2011] Zhao Caijun Jiang Quanxing and Jing Shenhui ldquoCalibration-independent and position-
insensitive transmissionreflection method for permittivity measurement with one sample in coaxial
linerdquo Electromagnetic Compatibility IEEE Transactions on vol 53 no 3 pp 684-689 Aug 2011
DOI 101109TEMC20112156416
[Catr1992] J Catrysse M Delesie and W Steenbakkers ldquoThe influence of the test fixture on
shielding effectiveness measurementsrdquo Electromagnetic Compatibility IEEE Transactions on vol 34
no 3 pp 348-351 August 1992 DOI 10110915155853
[Hasa2009] U C Hasar and C R Westgate ldquoA broadband and stable method for unique complex
permittivity determination of low-loss materialsrdquo Microwave Theory and Techniques IEEE
Transactions on vol 57 no 2 pp 471-477 Feb 2009 DOI 101109TMTT20082011242
[Hong2003] Y K Hong C Y Lee C K Jeong D E Lee K Kim and J Joo ldquoMethod and apparatus to
measure electromagnetic interference shielding efficiency and its shielding characteristics in
broadband frequency rangesrdquo Review of Scientific Instruments vol 74 no 2 pp 1098-1102 2003
DOI 10106311532540
[Krup2006] J Krupka ldquoFrequency domain complex permittivity measurements at microwave
frequenciesrdquo Measurement Science and Technology vol 17 p R55 2006 DOI 1010880957-
0233176R01
[Popo2005a] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric spectroscopy of
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302
Electromagnetic properties of nanostructured materials
University of York 52 10 July 2015
biological tissues at microwave frequenciesrdquo Microwave Theory and Techniques IEEE Transactions
on vol 53 no 5 pp 1713- 1722 May 2005 DOI 101109TMTT2005847111
[Popo2005b] D Popovic L McCartney C Beasley M Lazebnik M Okoniewski S C Hagness and J
H Booske ldquoCorrections on lsquoPrecision open-ended coaxial probes for in vivo and ex vivo dielectric
spectroscopy of biological tissues at microwave frequenciesrsquordquo Microwave Theory and Techniques
IEEE Transactions on vol 53 no 9 pp 3053 Sept 2005 DOI 101109TMTT2005854214
[RnS] Rhode amp Schwarz Application Note RAC-0607-0019 ldquoMeasurement of dielectric material
propertiesrdquo 23 March 2012 URL httpwww2rohde-schwarzcomfileRAC-0607-0019_1_5Epdf
[Sart2006] M S Sarto and A Tamburrano ldquoInnovative test method for the shielding effectiveness
measurement of conductive thin films in a wide frequency rangerdquo Electromagnetic Compatibility
IEEE Transactions on vol48 no2 pp 331- 341 May 2006 DOI 101109TEMC2006874664
[Toro2000] A Toropainen P Vainikainen and A Drossos ldquoMethod for accurate measurement of
complex permittivity of tissue equivalent liquidsrdquo Electronics Letters vol 36 no 1 pp 32-34 6 Jan
2000 DOI 101049el20000126
[Vasq2009] H Vasquez L Espinoza K Lozano H Foltz and S Yang ldquoSimple device for
electromagnetic interference shielding effectiveness measurementrdquo IEEE Electromagnetic
Compatibility Society Newsletter pp 62-68 Winter 2009 URL
httpwwwemcsorgacstrialnewsletterswinter09pp2pdf
[WikiMatSim] Wikipedia ldquoMatrix similarityrdquo Wikipediaorg URL
httpenwikipediaorgwikiMatrix_similarity [Last Modified 7 August 2012 at 2141]
[Wils1988] P F Wilson M T Ma and J W Adams ldquoTechniques for measuring the electromagnetic
shielding effectiveness of materials I Far-field source simulationrdquo Electromagnetic Compatibility
IEEE Transactions on vol 30 no 3 pp 239-250 August 1988 DOI 101109153302