APPLICATION OF NON-BIASED FERRITES FOR THE SUPPRESSION OF EMI

FROM RF TO MM WAVES

Karén Kocharyan

RENAISSANCE Electronics Corporation12 Lancaster County Rd., Harvard, MA 01451kkocharyan@rec-usa.com

IMS-2004 Workshop WMH

OVERVIEW

• Dispersion of Initial Magnetic Permeability• Ferrites for Wire Line EMI Filters• Ferrite Microwave Absorbers• MM-Wave Ferrites and Characterization• Conclusion

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COMMON AND DIFFERENTIAL MODES INWIRE LINES

S

L

NC

IDIC

ND

IS

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SUPPRESSING COMMON MODE NOISE WITH CHOKE COIL

S L

N

§ Frequency Characteristics § Design Limitations

1

2

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SUPPRESSING DIFFERENTIAL MODE WITH BAND-REJECT FERRITE FILTER

Differential Mode Noise and Signal at Different Frequency Bands

)Z(Z)ZZ(Z

log20IL(dB)LS

FLS10 +

++=

SL

ND

ZS ZL

ZF

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DISPERSION OF INITIAL MAGNETIC PERMEABILITY

I – Domain Wall ResonanceII – Natural Magnetic Resonance

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I

µ′

10000

1000

100

10

1

II

µ ′

µ ′′

0.1 1 10 100 1000 f (kHz)

µ ′′

1000

100

10

1

0.1

EQUIVALENT CIRCUIT OF INDUCTANCE INCORPORATING FERRITE CORE

XL(f) RS(f)

ZF = RS + XL

where

XL = ωL0µ′

RS = ωL0µ″

L0 ~ N2 − air core inductance

N − the number of turns

Ferrite EMI Filters operating at resistive mode do not introduce parasitic oscillations and signal distortions ! f

Z

XLRS

ZF

N = 3

2

1

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MAGNETOCRYSTALLINE ANISOTROPY AND NATURAL MAGNETIC RESONANCE

ω0 = γHint

Hint = H0 + HA + Hi (M)H0 — external magnetic field

HA — effective field of magnetocrystalline anisotropy

Hi(M) — magnetization-dependent terms

at H0 = 0, M = 0 and Hi (M) = 0

Hint = HAωNR = γHA

ωNR — frequency of natural magnetic resonance

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EVALUATING ANISOTROPY FIELD IN ISOTROPIC FERRITES

HA*) = 2K1/MS

K1 – constant of cubic anisotropy

µ′ ≅ MS2/3K1

HA ≅ 2MS/3µ′

*) Soft ferrite manufacturers usually do not specify this parameter

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E.W.Gorter, Proc. IRE 43, 245, (1955)

SNOEK’S LIMIT ON RF PERMEABILITY OF ISOTROPIC FERRITES

• CUBIC SYMMETRY IMPLIES LOW MAGNETIC ANISOTROPY:

|K1| ≤ 103 J/m3

HA < 104 A/m ≅ 100 Oe

fNR = 500 MHz

• S = fµ′ = 2γMS/3 = 5 GHz

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HEXAGONAL FERRITES WITH UNIAXIAL MAGNETIC ANISOTROPY

K1 – constant of axial anisotropyK2 – constant of in-plane anisotropy

K1 >> K2

K1 > 0 K1 < 0easy axis easy plane

C

M

C

M

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HA1 ~ 10,000 OeHA2 ~ 100 Oe

fNR = γ√(HA1× HA2) / 2π ~ 1GHz

S = γMS sin2θ0 (HA1/HA2)1/2 ~ 15 GHz

Jonker, Wijn and Brawn, Phillips, Tech. Rev., 18, 150 (1956-57)

SNOEK’S LIMIT ON PERMEABILITY OF EASY-PLANE HEXAFERRITES

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HEXAGONAL FERRITES WITH EASY-AXIS ANISOTROPY

TYPICAL CHARACTERISTICS

HA1 = 2000 - 20,000 OefNR = γHA1/ 2π ~ 6 - 60 GHz

µ ′, µ ″ ~ 0.5 - 3 ε ′ ~ 18 - 20

σ ~ 0.01 - 10 (MOhm m)-1

ε ″ ~ 0.02 - 10

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MICROWAVE FERRITE ABSORBERS FOR WIRELESS APPLICATIONS

• Broader Bandwidthµ is strongly dispersive

• Thinner Absorberk ~ (µ′ε″ + ε′µ″ ) / (µ′ε′)1/2

Available Forms

§ Ferrite Tiles § Ferrite Composites § Ferrite Paints

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METAL-TERMINATED FERRITE ABSORBER

§ Computational Methods

§ Matching Solution Map(Cole-Cole magnetic diagram)

10 20 00 .ZZZZdBRL *in

*in ≤+−⇒−<

= **

*

**in eµ

cpdfj

eµZ 2tanh

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BROADBAND FERRITE ABSORBER DESIGN PARAMETERS

INPUT PARAMETERS

§ Dispersion of Complex Magnetic Permeability§ Complex Dielectric Permittivity§ Required Suppression Level

OUTPUT PARAMETERRange for product - (fd)

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MM-WAVE MATERIAL CHARACTERIZATION METHODS

§ Waveguide- rectangular/cylindrical sample- deteriorating effect of the air gap- standard equipment

§ Coaxial Line- complicated sample geometry- moderate accuracy- standard equipment

§ Quasi-Optical- simple sample geometry- high accuracy- custom designed spectrometer

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BLOCK DIAGRAM OF QUASI-OPTICAL MM-WAVE BWO-SPECTROMETER*)

BWO

N

S

II

I

*)At TUFTS University, Medford, MA

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TECHNICAL CHARACTERISTICS OF BWO-SPECTROMETER

§ RADIATION SOURCE - Backward Wave Tubes§ RADIATION TYPE - Coherent, Tunable§ POLARIZATION - Linear/Circular§ DETECTORS - Diodes/Bolometer§ SCAN RANGE (GHz) - 35 - 56; 44 - 76; 70 - 120§ SCAN STEP - ≥ 3 MHz§ SCAN TIME (1000 point) - 1 min.§ DYNAMIC RANGE - > 40 dB§ MAGNETIC FIELD - up to 15 kOe

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EQUATIONS

( )[ ]( ) ( )r

r

i

t

AERERRRE

EET

ϕϕ++−

+−==2

02

0

20

20

2

sin41sin41

( ) ( )[ ]( ) ( )r

r

i

r

AERERAEER

EER

ϕϕ

++−++−==

20

20

220

2

sin41sin41

( )ckdfE π4exp −=

( )( ) 22

22

0 11

babaR

+++−=

−+=

12

22 bab

atanrϕ

*

**

εµ=≡+ Zjba

cndfA π2=

**εµ=− jkn

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APPROXIMATIONS

§ Dielectric Permittivity, ε* = ε′ - jε″ :

§ Magnetic Permeability, µ* = µ′ - jµ″ :

oriented ceramic:

randomly oriented:

Simulation Parameter Set

f

constσ

εε

ε2

0 +′′≡′′

=′

( )[ ] ( )

2222 fffffj ACMAC −−+=′′−′ µµ

( )[ ] ( )2222

32

31 fffffj ACMAC −−++=′′−′ µµ

πγπγα 2 ,2 , SMANRGNRAC MfHffjff ==+=

fNR, αG, fM , ε′, ε0″, σ

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EXAMPLE 1: LOW-LOSS CERAMIC

Frequency, GHz30 45 60 75 90 105 120

Ref

lect

ance

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9ExperimentTheory

Frequency, GHz40 60 80 100 120

Tra

nsm

itta

nce

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

ExperimentTheory

a) b)

MM-Wave transmission a) and reflection b) spectra of M-(easy-axis) type oriented Ba-hexaferrite ceramic. Wave propagation is along the direction of orientation. Sample thickness is 12.67 mm.

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EXAMPLE 1: BEST-FIT PARAMETERS

Frequency, GHz30 45 60 75 90 105 120

Rea

l Per

mea

bilit

y, µ

'

0

2

4

6

8

10

Imag

inar

y P

erm

eabi

lity,

µ'' ×

103

0

2

4

6

8

10

0.0918.80.0012< 0.0547.610.6

ε0″ε′αGσ (MOhm m)-1fNR (GHz)fM (GHz)

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EXAMPLE 2: LOSSY CERAMIC

Frequency, GHz30 45 60 75 90 105 120

Tra

nsm

itta

nce

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

Experiment Theory

Frequency, GHz30 45 60 75 90 105 120

Ref

lect

ance

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9ExperimentTheory

a) b)

MM-Wave transmission a) and reflection b) spectra of lossy M-(easy-axis) type oriented Ba-hexaferrite ceramic. Wave propagation is along the direction of orientation. Sample thickness is 9.67 mm.

0.7819.70.0011451.211.5

ε0″ε′αGσ (MOhm m)-1fNR (GHz)fM (GHz)

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CONCLUSION

§ In Wire Line EMI Applications the Anisotropy Field of Ferrite Core Should Match to the Noise Spectrum

§ Hexagonal Ferrites with Uniaxial Anisotropy are Suitable for Application at Short Microwaves

§ Quasi-Optical BWO Spectroscopy Allows Complete MM-Wave Characterization of Ferrite Materials

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