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Comparison of different structures of ferriteEMI suppressors
Mirjana Damnjanovic, Goran Stojanovic, Ljiljana Zivanov and Vladan Desnica
Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia
AbstractPurpose – Present 3D electromagnetic simulators have high accuracy, but they are time and memory expensive. Because of that, fast and simpleexpression for impedance is also necessary for initial inductor design. In this paper new efficient method for total impedance calculation of ferriteelectromagnetic interference (EMI) suppressor is given. By using an algorithm, it is possible to predict correctly all variations of electrical characteristicsintroduced by varying geometry parameters of EMI suppressor.Design/methodology/approach – The starting point for calculation of electrical characteristics of EMI suppressor is Greenhouse theory. Greenhousedecomposed inductor into its constituent segments. Basically, all segments of conductive layer are divided into parallel filaments having small,rectangular cross sections. The self- and mutual-inductance were calculated using the concept of partial inductance. Total impedance of EMI suppressoris calculated taking care of dimension of chip size, material that are used and geometry of conductive layer.Findings – The Simulator for Planar Inductive Structures (SPISe) simulates effects of ferrite materials and geometrical parameters of planar inductivestructures. With proposed software tool, designers can predict performance parameters quickly and easily before costly prototypes are built. SPISesoftware offers substantially reduced time to market, and increases device performance. The computed impedances, given by our software tool arecompared with measured data and very good agreement was found.Practical implications – Applied flexible efficient methods for impedance calculation of EMI suppressor are able to significantly increase the speeddesign of multilayer suppressors for universal series bus, low-voltage differential signaling and in other high-speed digital interfaces incorporated innotebooks and personal computers, digital cameras and scanners. Also, ferrite suppressors have been successfully employed for attenuating EMI inswitching power supplies, electronic ignition systems, garage door openers, etc.Originality/value – The paper presents realized structures of ferrite EMI suppressors. New geometries of conductive layer are proposed. In addition,using simple model of inductor, the paper develops a CAD simulation tool SPISe for calculation of electrical characteristics of EMI suppressors withdifferent geometry of conductive layer.
Keywords Electromagnetism, Attenuators
Paper type Research paper
Introduction
Electromagnetic interference (EMI) is a degradation in
performance of an electronic system caused by an
electromagnetic disturbance. With the increasing amount of
electronic equipment being used together in areas where they
can affect each other, the probability of EMI becomes higher.Most noise emitted from electronic equipment is at
frequencies higher than circuit signals. Therefore, low-pass
filters, which only pass signals with frequencies lower than a
specified frequency and attenuate signals with frequencies
higher than this frequency, are generally used as EMI filters
(Murata Manufacturing Co., Ltd, 1998).Multilayer suppressors have a wide range of applications,
such as EMI suppression in universal series bus, low-voltage
differential signaling and in other high-speed digital interfaces
incorporated in notebooks and personal computers, digital
cameras and scanners. Also, ferrite suppressors have been
successfully employed for attenuating EMI in switching power
supplies, electronic ignition systems, garage door openers, etc.
They suppress harmonic noise in products with higher clock
frequencies and minimize operation errors caused by local
oscillators in mobile products.The size, performance and reliability of multilayer
components make them very suitable for high density
mounting. They are made in Electronic Industries
Association EIA standard sizes: 0402, 0603, 0805, 1206
and 1210 (Figure 1) and they have impedance between 6 and
2000V at 100MHz (Ferroxcube Products Corp., 2001).
Ferrite EMI suppressors
Ferrite components have been used for reducing or
eliminating conducted EMI on printed circuit boards in
wiring and cables for decades (Naishadham, 1999;
Mardiguian, 2000; Keenan, 2003; Amemiya et al., 2002;
Kumar, 1999).In recent years, miniaturization of electronic devices, dense
mounting of components and higher clock frequencies,The current issue and full text archive of this journal is available at
www.emeraldinsight.com/1356-5362.htm
Microelectronics International
23/3 (2006) 42–48
q Emerald Group Publishing Limited [ISSN 1356-5362]
[DOI 10.1108/13565360610680758]
The present work was partially supported by the Ministry of Science,Technology and Development, Republic of Serbia, on Project NumberMNTR-006116B.
The authors would like to thank Littelfuse Ireland Limited, Dundalk,Co. Louth, for manufacturing ferrite EMI suppressors.
42
especially in the area of communication, computing and
information technology lead to a need for very small
suppression devices. Therefore, miniature chip components
have been developed for such situation.These multilayer components consist of highly conductive
layer embedded in ferrite monolithic structure, which
provides them a good magnetic shielding. These
components have been fabricated using the ceramic
coprocessing technology. Electrical characteristics of these
components depend on the geometry of conductive material
and core, and of the permeability of the core material m.The purpose of this paper is to explore design, modeling
and characterization of different structures of coils embedded
in the soft ferrites. In order to achieve that goal, a compact
computer program Simulator for Planar Inductive Structures
(SPISe) is developed as CAD tool for calculation of electrical
properties of different structures of ferrite multilayer
suppressors.The SPISe simulates effects of ferrite materials and
geometrical parameters of planar inductive structures. With
proposed software tool, designers can predict performance
parameters quickly and easily before costly prototypes are
built. SPISe software offers substantially reduced time to
market, and increases device performance.
Influence of ferrite material
Two different soft ferrite materials are used for realization of
these ferrite EMI suppressors (MMG Neosid Ltd, 2001):1 low permeability NiZn ferrite material, denoted LP
(which is used for suppression at high frequencies above
200MHz); and2 high permeability NiZn ferrite material denoted HP
(which is used for suppression over a wide range of
frequencies from 20 to 200MHz).
The permeability of the ferrite material is a complex
parameter consisting of a real mr0 and imaginary part mr
00;both parts of the permeability are frequency dependent. They
intersect at ferrimagnetic resonant frequency, as it can be seen
in Figure 2.Owing to the presence of ferrite core, multilayer suppressor
behaves as a frequency dependent resistor. At low
frequencies, losses in inductor are low. Losses start to
increase as frequency increase; at ferrimagnetic resonant
frequency, the inductor behaves as a frequency-dependent
resistor and no longer as a true inductance. This is very
important in elimination of conducted EMI.Along with the desired insertion loss of the inductor,
parasitic effects such as inter-turn and inter-winding
capacitance, self-resonance, dielectric and magnetic losses of
the core, etc. play an important role in the design of such
component (Naishadham, 1999).
Influence of conductive paste
Outside the range of frequencies where conducted EMI has to
be eliminated, the inductor must have low losses. To obtain
that goal, for conductive layer has to be chosen material with
high conductivity.If the conductivity of conductive paste is higher, direct
resistance RDC of EMI suppressor is smaller. As the frequency
increases, magnetic losses dominate and the total impedance
of suppressor is determined by the characteristics of ferrite
material. However, the ratio of maximal total impedance
ZMAX and resistance RDC of ferrite EMI suppressor will be
bigger if conductivity of conductive paste is higher (i.e. better
EMI suppression will be achieved).The influence of three different conductive pastes: silver Ag,
platinum Pt and silver-palladium PdAg (Du Pont, 2001)
on the total impedance is observed in Damnjanovic et al.
(2004a,b).Platinum conductive paste is used for realization of
proposed EMI suppressors.
Influence of structure of conductive layer
Besides the characteristics of materials, the geometry of
conductive layer determines the total impedance, also.
Because of that, it is very important to choose appropriate
structure of suppressor.Configuration of conductive layer of simple structures of
EMI suppressors are shown in Figure 3 (before upper ferrite
layer is put on):. narrow line (width w ¼ 450mm, length l ¼ 2.01mm and
thickness t ¼ 10mm);. wide line (w ¼ 950mm, l ¼ 2.01mm, t ¼ 10mm);. zig-zag (w ¼ 50mm, length of segments l ¼ 1mm,
t ¼ 10mm and angle between segments a ¼ 758); and. meander (w ¼ 150mm, t ¼ 10mm, length of segments
l ¼ 1mm, pitch between two neighboring segments
p ¼ 450mm).
Mechanical dimensions of realized EMI suppressor are
standard EIA size 0805, as it is shown in Figure 4
Figure 1 Range of multilayer suppressors in standard EIA sizes0402-1812
Figure 2 Complex permeability vs frequency for high permeability NiZnferrite material (MMG Neosid Ltd)
Comparison of different structures of ferrite EMI suppressors
Mirjana Damnjanovic et al.
Microelectronics International
Volume 23 · Number 3 · 2006 · 42–48
43
(D ¼ 1.1mm, E ¼ 0.25mm ^ 0.075, L ¼ 2.01mm ^ 0.2,
W ¼ 1.25mm ^ 0.20).The size of suppressor determines its electrical
characteristics. The influence of dimensions of suppressor is
observed in Aharoni (1998). The calculation of
demagnetizing factor is built in simulation tool SPISe.
Calculation of electrical characteristics of EMIsuppressors
To obtain the optimal design of inductor it is much more
convenient to use some simulation tool, than make a specific
test component. Because of that, the simulation tool SPISe
for calculation of impedance of ferrite EMI suppressor is
developed.
Model of EMI suppressor
Simulation tool SPISe is built upon simple equivalent circuit
model of an inductor, which is shown in Figure 5 (Yu and
Holmes, 2002; Kim et al., 2002). The equivalent series
resistance of the inductor R is caused by losses in the
conductive material and magnetic losses. Usually, for ferrite-
core inductors the core losses dominates at RF:
R ¼ vm00
r L0; ð1Þ
where L0 is inductance of the coil with the core removed
(Reggiani et al., 2002; Bartoli et al., 1994). Inductance L isequivalent series inductance of the inductor:
L ¼ m0
rL0: ð2Þ
The equivalent lumped capacitance of the inductor Crepresents the parasitic effects of the conductive material.Using the equivalent circuit of an inductor the total
impedance Z can be determined as:
Zð jvÞ ¼ R þ j · ðvLð12 v2LCÞ2 vR2CÞð12 v2LCÞ2 þ v2R2C2
: ð3Þ
From the expressions (1)-(3), it can be shown that the totalimpedance of the inductor Z can be increased by increasingL0 (e.g. by optimal design of the geometry of the conductive
layer), or by choosing the appropriate ferrite material.
Simulation tool SPISe
The calculation of impedance of zig-zag or meander structure
of inductor is very complex. Therefore, the segments ofmeander and zig-zag structure are divided into parallelfilaments having small, rectangular cross sections. Taking care
of the current flow, to every filament is assigned vector, as itcan be seen in Figure 6. The self- and mutual-inductancewere calculated using the concept of partial inductance
(Ruehli, 1972; Ruehli et al., 1995; Greenhouse, 1974).For straight conductor of rectangular cross section self-
inductance is:
Li ¼ 2 · l · ðln 2l
w þ tþ 0:25049þ w þ t
3lþ m
4T Þ ðnHÞ; ð4Þ
where Li is the inductance in (nH); l, w and t are length, widthand thickness of the conductor in (cm), respectively, m is the
Figure 3 Realized structures of EMI suppressor
Figure 4 Mechanical dimensions of realized EMI suppressor –standard EIA size 0805
Figure 5 Equivalent circuit model of an inductor
Figure 6 Calculation of total impedance of meander coil by using theconcept of partial inductance
Comparison of different structures of ferrite EMI suppressors
Mirjana Damnjanovic et al.
Microelectronics International
Volume 23 · Number 3 · 2006 · 42–48
44
conductor’s permeability, and T is a frequency-correction
parameter.The mutual inductance between two straight parallel
conductors of rectangular cross section can be calculated as:
Lij ¼ 2l lnl
GMDþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ l
GMD
� �2s0
@1A
0@
2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ GMD
l
� �2s
þGMD
l
1A;
ð5Þ
where l is the conductors’ length, GMD is geometric mean
distance between the conductors:
lnGMD ¼ ln d 21
12
d
w
� �2
þ 1
60
d
w
� �4
þ 1
168
d
w
� �6
þ 1
360
d
w
� �8
þ 1
660
d
w
� �10
þ. . .
!:
ð6Þ
Assume that a conductive layer of suppressor is divided into n
filaments with rectangular cross sections. Then the total
inductance of structure L can be calculated as the sum of
partial self-inductances of all elementary filaments and the
sum of all mutual inductances between all elementary
filaments:
L ¼Xn
i¼1
Li þXn
i¼1
Xn
j¼1
Lij ; where i – j: ð7Þ
Using these formulae the simulation tool SPISe was
developed. Computation concept of electrical characteristics
of ferrite EMI suppressor is described in Stojanovic et al.
(2006), where is explained with more details calculation of its
resistance and capacitance.Some basic steps of the algorithm of simulation tool SPISe
are shown in Figure 7. Firstly, designer has to choose chip
size, ferrite material, conductive paste and structure of EMI
suppressor. Then, user has to set desired values for
dimensions of selected structure. Based on all initial values
of input data, the simulation tool SPISe will make test if the
values of input parameters are correct (in allowed range).
Then, if everything is correct, SPISe will determine the
maximal number of turns Nmax for meander and zig-zag
structure. User can choose number of turns N not greater
than Nmax.Subroutine KOORD will determine set of vectors, which
will describe selected structure of EMI suppressor (as it can
be seen for meander structure in Figure 6). After that,
calculation of self- and mutual-inductance are conducted
(subroutines LS and M, respectively), and of all other
electrical parameters of EMI suppressor.The simulation tool SPISe offers many possibilities to
design the EMI suppressor with best performance. This
simulation tool can be used for calculation of electrical
characteristics of more complex structures (Damnjanovic
et al., 2004a,b; Raghavendra et al., 2004).
Results of simulation and measurement
In order to design EMI suppressors with the best
performance, with taking care of range of unwanted
frequencies that can occur, designer have to selectappropriate conductive paste and ferrite material. In this
paper, simulation results obtained for four different EMI
suppressor structures and two different ferrite materials willbe compared with measurement results.Realized EMI suppressors were electrically tested in the
range of frequencies from 1MHz to 3GHz using Agilent4287A RF LCR meter.Comparison of measured and calculated values of total
impedance Z for narrow line in low permeability LP ferritematerial is shown in Figure 8. At low frequencies (up to
3MHz), losses in suppressor are low. As frequency increases,
series resistance RS dominates and suppressor behaves as afrequency-dependent resistor. This suppressor can be used for
suppression of unwanted frequencies above 200MHz.
Figure 7 Algorithm of simulation tool SPISe
Comparison of different structures of ferrite EMI suppressors
Mirjana Damnjanovic et al.
Microelectronics International
Volume 23 · Number 3 · 2006 · 42–48
45
If the conductor’s line is wider, for the same ferrite materialLP, inductance L and dc resistance RDC decrease. Because ofthat, series resistance RS and reluctance XL decrease, andhence, total impedance Z will be smaller.On the other hand, if the conductive line is longer, than
inductance L0 is bigger (see zig-zag and meander), andinductance L and impedance Z of structure will be bigger. InFigure 9 and Figure 10 simulation and measurement results
of inductance L and total impedance Z for all four structuresin LP soft ferrite material are compared, except for meander,because the measurement was not successful.As it can be seen from these figures, very good agreement
between measured (dot line) and calculated values (solid line)of inductance L and total impedance Z were found for lowpermeability LP ferrite material. Difference was less than
5 percent.Note that dependence of total impedance vs frequency
Z ¼ f(freq) for low permeability soft ferrite material have the
same shape for all structures (narrow and wide line, zig-zagand meander). At high frequencies the shape of dependenceZ ¼ f(freq) is determined by the characteristics of ferritematerial (equations (1) and (2)):
Z ¼ R þ jvL < jvL0ðm0
r 2 jm00
r Þ: ð8Þ
The same conclusion can be made for dependence ofinductance vs frequency L ¼ f(freq) in LP ferrite (Figure 9).
The shape of dependence L ¼ f(freq) is determined by the
characteristics of ferrite material (equation (2)).In Figure 11 and Figure 12 simulation and measurement
results for HP soft ferrite material are presented, except for
narrow line, because the measurement was not successful.
This nickel-zinc ferrite has low loss factor at low frequencies
(up to 1MHz), while high suppression impedance over
100MHz.
Figure 8 Simulated values of RS, XL and Z and measured values of Z fornarrow line in LP ferrite
Figure 9 Measured and calculated inductance for all structures in LPferrite material
Figure 10 Measured and calculated total impedance for all structuresin LP ferrite material
Figure 11 Measured and calculated inductance for all structures in HPferrite material
Figure 12 Measured and calculated total impedance for all structuresin HP ferrite material
Comparison of different structures of ferrite EMI suppressors
Mirjana Damnjanovic et al.
Microelectronics International
Volume 23 · Number 3 · 2006 · 42–48
46
As it can be seen from this figures, dependence of total
impedance vs frequency Z ¼ f(freq) for high permeability
ferrite material have the same shape for all structures. This
dependence Z ¼ f(freq) is determined by the characteristics of
HP ferrite material. Good agreements between measured and
calculated values were found. Difference between measured
and calculated values was less than 10 percent.In Table I, comparison of measured and simulated values of
RDC, ZMAX, ZMAX/RDC for simple EMI suppressor structures
is presented.If calculated values of total impedance Z for the same
structure of conductive layer and two different ferrite
materials are compared (e.g. wide line), it can be noticed
that LP material has better ratio of ZMAX and RDC (RDC is
smaller and ZMAX is bigger).
Conclusion
Ferrite EMI suppressors consist of highly conductive layer
embedded in a ferrite monolithic structure. The total
impedance of the suppressor depends of permeability of
core material m and of geometry of the conductive material
and core.The influence of two ferrite materials (low LP and high HP
permeability material) and four structures of conductive layer
(narrow and wide line, zig-zag and meander) on electrical
characteristics of EMI suppressors is presented in this paper.If the conductor’s line is wider, inductance L and dc
resistance RDC decrease. Because of that, series resistance RS
and reluctance XL decrease, and hence, total impedance Z
will be smaller. On the other hand, if conductive line is longer
(like for zig-zag and meander structure), than inductance L0 is
bigger, and inductance L and impedance Z of structure will be
bigger. The biggest inductance and impedance has meander,
then zig-zag, narrow line and wide line.In order to determine electrical characteristics of EMI
suppressors simulation tool SPISe is developed. With
proposed software tool, designers can predict performance
parameters quickly and easily before costly prototypes are
built. SPISe software offers substantially reduced time to
market, and increases device performance.
In addition, realized EMI suppressors were electricallytested. Results of measurements and calculation of electricalcharacteristics of EMI suppressors have been compared. Agood agreement was found.These results will be very useful for construction of the
ferrite EMI suppressors with optimal performance.
References
Aharoni, A. (1998), “Demagnetizing factors for rectangularferromagnetic prism”, Journal of Applied Physics, Vol. 83,pp. 3432-4.
Amemiya, F., Takagi, K., Kuwebara, N., Hamada, S. andIwamoto, Y. (2002), “Developing a common-mode chokecoil with high-permeability core used high-speedtelecommunications port for UTP cable”, IEEEInternational Symposium on EMC, Vol. 1, pp. 314-9.
Bartoli, M., Reatti, A. and Kazimierczuk, M.K. (1994),“High frequency models of ferrite core inductors”, IEEETransactions on Magnetics, pp. 1670-5.
Damnjanovic, M., Zivanov, L. and Stojanovic, G. (2004a),“Influence of geometry of conductive layers and differentferrites on impedance of EMI suppressor”, paper presentedat the 16th International Conference on ElectricalMachines – ICEM 2004, PS6-28.
Damnjanovic, M., Zivanov, L., Stojanovic, G. and Desnica,V. (2004b), “Modeling and simulation of impedance offerrite EMI suppressor with two conductive layers”, IEEE24th International Conference on Microelectronics MIEL 2004,Vol. 1, pp. 245-8.
DuPont (2001), technical information available at: www.dupont.com
Ferroxcube Products Corp. (2001), “Multilayer suppressorsand inductors”, available at: www.ferroxcube.com
Greenhouse, H.M. (1974), “Design of planar rectangularmicro-electronic inductors”, IEEE Transactions on Parts,Hybrids and Packages, Vol. PHP 10, pp. 101-9.
Keenan, A. (2003), “Board level EMI suppression usingferrite components”, IEEE International Symposium onEMC, Vol. 2, pp. 1252-4.
Kim, T.H., Lee, J., Kim, H. and Kim, J. (2002), “3GHz widefrequency model ferrite bead for power/ground noisesimulation of high-speed PCB”, paper presented at IEEEConference on Electrical Performance of ElectronicPackaging, October 21-23, pp. 217-20.
Kumar, K. (1999), “Leadless devices for EMI suppression”,Proceedings International Conference on Electro-magneticInterference and Compatibility, pp. 343-56.
Mardiguian, M. (2000), EMI Troubleshooting Techniques,McGraw-Hill, New York, NY.
MMG Neosid Ltd (2001), “Soft ferrite materials”, availableat: www.mmg-neosid.com
Murata Manufacturing Co., Ltd (1998), “Basics of EMIfilters”, available at: www.murata.com
Naishadham, K. (1999), “A rigorous experimentalcharacterization of ferrite inductors for RF noisesuppression”, paper presented at IEEE Radio andWireless Conference, RAWCON 99, August 1-4, pp. 271-3.
Raghavendra, R., Bellew, P., Mcloughlin, N., Stojanovic, G.,Damnjanovic, M., Desnica, V. and Zivanov, L. (2004),“Characterization of novel varistor þ inductor integratedpassive devices”, IEEE Electron Devices Letters, Vol. 25No. 12, pp. 778-80.
Table I Measured and calculated values of RDC, ZMAX, ZMAX/RDC andonly calculated for narrow line in HP and meander in LP material
Measurement Calculation
RDC (V) ZMAX (V)
ZMAX/
RDC RDC (V) ZMAX (V)
ZMAX/
RDC
LP ferrite at 1.65 GHz at 1.62 GHz
Narrow line 1.15 45.7 41.54 1.08 46.44 43.00
Wide line 0.40 29.5 74.31 0.38 29.98 78.89
Zig-zag 4.87 88.9 18.25 5.31 90.58 17.06
Meandera – – – 7.99 120.22 15.05
HP ferrite at 0.81 GHz at 0.81 GHz
Narrow linea – – – 2.06 33.8 16.42
Wide line 1.40 24.3 17.36 1.34 25.46 19.00
Zig-zag 7.23 76.4 10.51 6.72 71.11 10.58
Meander 10.70 101.0 9.44 9.89 90.48 9.14
Note: aFor narrow line in HP material measurement was not successful
Comparison of different structures of ferrite EMI suppressors
Mirjana Damnjanovic et al.
Microelectronics International
Volume 23 · Number 3 · 2006 · 42–48
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Reggiani, U., Grandi, G., Sancineto, G., Kazimierczuk, M.K.and Massarini, A. (2002), “High-frequency behavior oflaminated iron-core inductors for filtering applications”,IEEE Transactions on Magnetics, pp. 654-60.
Ruehli, A.E. (1972), “Inductance calculations in a complexintegrated circuit environment”, IBM Journal Res. Develop.,Vol. 16, pp. 470-82.
Ruehli, A., Paul, C. and Garret, J. (1995), “Inductancecalculations using partial inductances and macromodels”,IEEE Proceedings International Symposium on EMC, August14-18, pp. 23-7.
Stojanovic, G., Damnjanovic, M., Desnica, V., Zivanov, L.,Raghavendra, R., Bellew, P. and Mcloughlin, N. (2006),“High performance zig-zag and meander inductors
embedded in ferrite material”, Journal of Magnetism and
Magnetic Materials, Vol. 297 No. 2, pp. 76-83.Yu, Q. and Holmes, T.W. (2002), “RF circuit modeling of
ferrite-core inductors and characterization of core
materials”, IEEE Transactions on Electromagnetic
Compatibility, Vol. 44 No. 1, pp. 258-63.
Corresponding author
Mirjana Damnjanovic can be contacted at: [email protected].
ac.yu
Comparison of different structures of ferrite EMI suppressors
Mirjana Damnjanovic et al.
Microelectronics International
Volume 23 · Number 3 · 2006 · 42–48
48
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