DEVELOPMENT AND INVESTIGATION OF …• Development and investigation of approximate phenomenological models describing and estimating the coupling of EM energy through apertures into

I E E E S o u t h e a s t e r n M i c h i g a n E M C S o c i e t y

ION OF ODELS FOR

IC ENERGY OSURES

V I S T E O N C O R P O R A T I O N

DEVELOPMENT AND INVESTIGATAPPROXIMATE PHENOMENOLOGICAL M

THE COUPLING OF ELECTROMAGNETTHROUGH APERTURES INTO ENCL

I. Belokour

EMC APPLICATIONS ENGINEERING

VISTEON CORPORATION

ation)

he EM Field Coupling

ng Wall

Outline

1.0 Introduction

1.1 EM Interference and Susceptibility of Electronic Systems

1.2 Problem Definition

2.0 Developement of Models in EMC

2.1 Topological Decomposition of Systems (Physical Configur

2.2 Topological Decomposition of Systems (Shielding Topolog

2.3 Modeling Techniques Used in EMC for the Estimation of t

2.4 Modeling and Simulation Validation

3.0 Some EMC Concepts Relevant to Shielding

3.1 Shielding Effectiveness

3.2 Electrically Small Apertures in an Infinitely Thin Conducti

EM Field

of the EM Field

ture Dimensions

binations of Apertures

ith Aperture

4.0 Application of the TL Method to the Estimation of the

Penetration into an Enclosure with Aperture

4.1 Approximations Based on a TL Model

4.2 Approximations Based on a Multimode TL Model

4.3 Introduction of Losses into an Enclosure

4.4 Aperture-Enclosure Resonance Condition

5.0 Application of the FDTD Technique to the Estimation

Penetration into an Enclosure with Aperture

5.1 Shielding Effectiveness of an Enclosure with Various Aper

5.2 Shielding Effectiveness of an Enclosure with Various Com

6.0 Experimental Investigation of the SE of an Enclosure w

7.0 Conclusions

n aircraft

al models describing

enclosures

1.0 Introduction

1.1 EM Interference and Susceptibility of Electronic Syste

1.1.1 Intentional and Unintentional EM Interference

• careless people - operate their equipment during the landing of a

• terrorists - try to defeat electronics used by law-enforcement age

1.1.2 Countermeasures to EM Terrorism:

• Teaching design engineers

• Estimating and testing susceptibility levels

• Hardening electronic equipment

• Special detectors that warn about EM attacks

1.2 Problem Definition

• The analysis of available analytical and numerical techniques

• Development and investigation of approximate phenomenologic

and estimating the coupling of EM energy through apertures into

roper EMC design

2.0 Development of Models in EM

Figure 1. Model development in EMC

Modeling is a primary aspect in developing a correct and p

for a new product

• describe the physical configuration of a problem

• define the electrical configuration

• develop the electrical model

Configuration

Physical

System Topology

ElectricalModel

s (Physical

iagram: physical

d EM field

2.1 Topological Decomposition of SystemConfiguration)

Figure 2. An example of an aircraft and its EM topological dconfiguration

Cloud-to-cloud lightning

Radiate

lding Topology)

gram: EM shielding

tration

t injection of energy

Antenna

2.2 Topological Decomposition of Systems (Shie

Figure 3. An example of an aircraft and its EM topological diatopology.

Aperture penetration Diffusive pene

Barrier S1aircraft fuselage

Exteriorvolume V0

CircuitsCableShields

Incident EM field

e Estimation of

ulation of EM field

Tx-linematrixmethod

Curve-fittingto a model

techniques

method

nsientes

Semi-empirical

2.3 Modeling Techniques Used in EMC for ththe EM Field Coupling

Figure 4. Basic modeling techniques used in EMC for the simpenetration through finite apertures

Mathematical formulations equations

Maxwell

Analyticaltechniques

Numericaltechniques

Approximateengineering

formulas

MoM FEM FDTD

Quasi-staticapproach

Tx-line

methodmethodPower balance

method

method method

Numericaltechniques

method

Power balancemethod

approximationsAperture LF HF and tra

respons

Hybridmethod

approximations

Geometricaloptics

Apertu

Boundary conditions

to cover other

l responses

at system resonances,

2.4 Modeling and Simulation Valida

Model Validation Using Experimental Methods

• making a measurement of the same effect, then extend the model

configurations which will not be measured

Model Validation Using Non Experimental Methods

• using other validated models to validate a new model

Concepts Frequently Used to Examine the Validity of a M

• conservation of energy

• causality

• time of arrival of waveform response components

• low-frequency or high-frequency asymptotic behavior of spectra

• other known physical constraints of the solution, such as finite Q

hielding

ld strength of the trans-

ength in free space

3.0 Some EMC Concepts Relevant to S

3.1 Shielding Effectiveness

for electric fields

and for magnetic fields

where or is the incident field strength, and or is the fiemitted wave as it emerges from the shield.

An engineering formula used for enclosures with apertures

where l is the longest dimension of the aperture and is the wavel

Se 20 Ei Et⁄log=

Sm 20 Hi Ht⁄log=

Ei Hi Et Ht

Se 20 λ2l-----log=

ucting Wall

an electric dipole

a small aperture are and are the normal Ht

3.2 Electrically Small Apertures in an Infinitely Thin Cond

Figure 5. Electric and magnetic dipoles of an ape

The aperture is equivalent to a magnetic dipole and

, where the electric and magnetic polarizabilities ofgiven correspondingly by and , electric field and the tangential magnetic field, respectively.

CircularAperture

an̂ a

M αmHt–=

P ε 0αeEn–=αe 2a

33⁄–= αm 4a

33⁄= En

the ground plane is

uced tangential mag-icular polarizations

transmitted wave as it mitted wave at normal

and Ensc

The total transmitted power for dipoles radiating in the presence of

where is the intrinsic impedance of free space, and are indnetic and normal electric dipole moments. For parallel and perpendrespectively

The normalized shielding effectiveness

where is the incident field strength, is the field strength of theemerges from the shield, and is the field strength of the transincidence and parallel polarization.

4πη0

3λ2------------ k

η0 M P

Htansc

2Hi and Ensc

2Ei θisin= = Htan

sc2Hi θi

SEnor 20–Et Ei⁄

EtrefEi⁄

--------------------------

Ei EtEtref

ation of the EM Aperture

aperture

4.0 Application of the TL Method to the EstimField Penetration into an Enclosure with

4.1 Approximations Based on a TL Model

Figure 6. Geometry of a rectangular enclosure with

Incident field

e with aperture

e impedance

Figure 7. The equivalent circuit of the rectangular enclosur

The aperture is represented as a length of coplanar TL. The apertur

where is the aperture characteristic impedance.

A Pp d-p

Zgkg Zgk

Z0S, k0

Zap j Z0s

l2a------ 0.5k0ltan=

acteristic impedance

le system topology

lower frequencies

The enclosure is represented by the shorted waveguide whose char and propagation constant are respectively

The electric and magnetic shielding effectiveness are given by

The TL model

• gives good predictions of the electric and magnetic SE for a simp

• does not consider higher-order TE and TM modes, i.e., limited to

• does not include the polarization of the incident EM field

Zg Z0 1 λ 2a⁄( )2–⁄= kg k0 1 λ ⁄(–=

Se 20 Vp V'p⁄log– 20 2Vp( ) V⁄log–= =

Sm 20 Ip Ip'⁄log– 20 2IpZ0( ) ⁄log–= =

rectangular enclosure

tric SEnetic SE

Figure 8. Electric and magnetic shielding effectiveness of an emptywith aperture

0 200 400 600 800−20

Frequency, MHz

ElecMag

e TL Model

sure with aperture

4.2 Approximations Based on a Multimod

Figure 9. The equivalent circuit of an empty rectangular enclo

The equivalent source voltage with source impedance, respecti

Zs Zlm0 Z

y = py = 0

Zgm0Zap

+- Vpm0

Enclosure Equivalent CiEquivalent Source Circuit

Vs V0Zap Z0 Zap+( )⁄=

Zs Z0Zap Z0 Zap+( )⁄=

ctric mode of

gnetic mode of

ely as

The waveguide characteristic impedance of the m-th transverse elepropagation and the propagation constant are given respectively as

, where

The waveguide characteristic impedance of the m-th transverse mapropagation and the propagation constant are respectively

where the cutoff wavelength and mode number are given respectiv

Zgm0 Z0 1 mλ 2a⁄( )2–⁄=

kgm0 k0 1 mλ 2a⁄( )2–= m 1 2 3, ,=

Zgm1 Z0 1 mλ λc⁄( )2–⁄=

kgm1 k0 1 mλ λc⁄( )2–=

λc 2a 1 a b⁄( )2+⁄= m 1 2 3 …, , ,=

d in the direction of the

e for the m-th mode.

the Tx-line, viewed in e , are given Vlm0

The impedance of the m-th mode at point P on the TL, viewetermination is

where is the normalized termination impedanc

The effective impedance at test location P considering i

The source impedance of the m-th mode at test location P onthe direction of the source impedance , and the equivalent voltagrespectively as

Zrm0Zl

Zl jZgm0 kgm0 d p–( )[ ]tan+

1 jZnm0 kgm0 d p–( )[ ]tan+-------------------------------------------------------------------------=

Znm0 Zl Zgm0⁄=

Zrm0 jZgm0 kgm0 d p–( )tan=

Zlm0Zs

Zs jZgm0 kgm0 p( )tan+

1 jZnm0 kgm0 p( )tan+-----------------------------------------------------------=

Vlm0 Vs kgm0 p( )cos jZnm0 kgm0 p(sin+[⁄=

espectively

spectively

pectively as

Zlm0 Zrm0+( )⁄

0 Zrm0+ )

The m-th mode voltage and the total voltage at test location P are r

The m-th mode current and the total current at test location P are re

The electric and magnetic shielding effectiveness is determined res

where in the absence of the enclosure

Vpm0 Vlm0Zrm0 Zlm0 Zrm0+( )⁄= Vtp Vlm0Zrm0m

Ipm0 Vlm0 Zlm0 Zrm0+( )⁄= Itp Vlm0 Zlm(⁄

SEe 20 Vtp Vp0⁄ log– 20 2Vtp V⁄log–= =

SEm 20 Itp Ip0⁄ log– 20 2ItpZ0 V⁄log–= =

V0 2⁄= Ip0

V0 2Z0⁄=

bounded medium

41.4 3535.5 4031,1

50.1 3716.5 4190.8

986 0.0848 0.0744

2 …, ,2 …, ,3 …, ,

m n 0≠=

3 …, ,3 …, ,2 …, ,

m n 0≠=

Higher-Order Modes

The resonant frequencies of the , modes and un

wavelengths of the rectangular enclosure with aperture

Table 1.

Mode order 1 2 3 4 5

, MHz 707.11 1118.0 1581.1 2061.6 2549.5 30

,MHz 1346.3 1600.8 1952.6 2358.5 2795.1 32

, m 0.4242 0.2683 0.1897 0.1456 0.1177 0.0

TEzm0 TM

fres( )TEmnp

2π µε----------------- mπ

d-------

2 nπb

------ 2 pπ

a------

m 0 1,=

n 0 1,=

p 1 2,=

fres( )TMmnp

2π µε----------------- mπ

d-------

2 nπb

------ 2 pπ

a------

m 1 2,=

n 1 2,=

p 0 1,=

.3 m, p = 0.25 m) with mulation.

4000 4500

Figure 10. The of the enclosure (a = 0.3 m, b = 0.12 m, d = 0aperture (l = 0.025 m, w = 0.005 m) obtained by TL si

0 500 1000 1500 2000 2500 3000 35000

Frequency, MHz

.3 m, p = 0.25 m) with mulation.

000 4500

Figure 11. The of the enclosure (a = 0.3 m, b = 0.12 m, d = 0aperture (l = 0.025 m, w = 0.005 m) obtained by TL si

1000 1500 2000 2500 3000 3500 4−10

Frequency, MHz

.3 m, p = 0.25 m) with simulation.

4000 4500

Figure 12. The of the enclosure (a = 0.3 m, b = 0.12 m, d = 0aperture (l = 0.025 m, w = 0.005 m) obtained by FDTD

0 500 1000 1500 2000 2500 3000 3500

Frequency, MHz

TE10 TE20

TE40 TE50

TE60 TE70

suresorrection factor in

ectangular enclosure

porating the losses

4.3 Introduction of Losses into EncloDistributed losses can be modeled in TLs by including a complex cthe expressions for characteristic impedance and propagation cons

Characteristic impedance

Propagation constant

The effect of losses:

• mimic the loading effect of electronics

• appreciably dampen higher-order mode resonances of an empty r

thus improving the SE of the high-Q enclosure at higher frequen

• the higher-order mode resonant frequencies are lowered by incor

1 mλ 2a⁄( )2–

------------------------------------------- 1 γ gm0 jγ gm–+(=

klgm0 k0 1 mλ 2a⁄( )2– 1 γ gm0 jγ gm–+(=

.3 m, p = 0.25 m) with ed by TL simulation

4000 4500

a=0a=0.01a=0.05a=0.1

Figure 13. The of the enclosure (a = 0.3 m, b = 0.12 m, d = 0aperture (l = 0.025 m, w = 0.005 m) with incorporated losses obtain

500 1000 1500 2000 2500 3000 35000

Frequency, MHz

gammgammgammgamm

ndition

e enclosure with aper-

4.4 Aperture-Enclosure Resonance Co

The condition of the aperture-enclosure resonance is determined as

where the dominant-mode reactance

is compensated by the sum of the equivalent source reactance

and the reactance due to non-propagating higher-order modes in thture

Xs Xhm+ Xd=

Xd Im Zgm0( ), m 1==

Xs Im Zs( )=

Xhm Im Zgm0m

, m 1≠=

m)-enclosure (a = 0.3 y TL simulation

900 1000

.1 m mbda/2

Figure 14. SE degradation at the aperture (l = 0.2121 m, w = 0.005m, b = 0.12 m, d = 0.3 m, p = 0.25 m) resonance obtained b

0 100 200 300 400 500 600 700 800

Frequency,MHz

omparison of TL and

Tx−lineFDTD

Figure 15. SE degradation at the aperture-enclosure resonance. cFDTD simulations

0 200 400 600 800

Frequency, MHz

stimation of the th Aperture tational Space x 140 x 68 cells

5.0 Application of the FDTD Technique to the EEM Field Penetration into an Enclosure wi

Figure 16. FDTD model geometry

Incident field

Incidence plane

FDTD Compu 140

Figure 17. Incident field

0 0.5 1 1.5 2 2.5 3 3.5 4

1Electric Field

Time [ns]

Figure 18. Fourier transform of the incident fi

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

−4 Fourier Transform of Electric Field

Frequency [GHz]

ot length for TL and

Figure 19. Normalized shielding effectiveness vs. normalized slFDTD models

0.2 0.3 0.4 0.5 0.6 0.7 0.80

Normalized slot length

idth for TL and FDTD

Tx−lineFDTD

Figure 20. Normalized shielding effectiveness vs. normalized slot wmodels

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

Normalized slot width

number of slots

FDTD Tx−line

Figure 21. Normalized shielding effectiveness vs. the

2 3 4 5 6 7 80

No. of apertures

ormal incidence and

900 1000

FDTDTx−line

Figure 22. Shielding effectiveness for FDTD and TL model at nparallel polarization.

100 200 300 400 500 600 700 800−20

Frequency, MHz

Comparison of SE for FDTD and Tx−line model

Enclosure with

Transmit antenna

6.0 Experimental Investigation of the SE of anAperture

Figure 23. Shielding effectiveness measurement

Ground plane

E-field probe

HP8753D

Enclosure under test

Network analyzer

Port 1Port 2

led empty rectangular

00 1000

closure

Figure 24. Shielding effectiveness of the electromagnetically seaenclosure

300 400 500 600 700 800 90

Frequency, MHz

Sealed en

00 1000

rmentse

Figure 25. Computed and measured shielding effectiveness of thewith aperture of 0.1 by 0.005 m.

300 400 500 600 700 800 9−10

Frequency, MHz

FDTDMeasuTx−lin

00 1000

rmentse

Figure 26. Computed and measured shielding effectiveness of thewith aperture of 0.05 by 0.005 m.

300 400 500 600 700 800 9−10

Frequency, MHz

FDTDMeasuTx−lin

method

iation and the number

omparing the relative

gainst some standard

age by geometrically

, it is better to have

an aperture has been

ividual as well as

considered

d to mimic the loading

7.0 Conclusions• SE of a rectangular enclosure has been investigated using the TL

• an estimate of the SE depending on the slot length and width var

of slots has been developed. The developed method is good for c

shielding of different slot sizes or comparing relative shielding a

• energy transfer into an enclosure may be reduced at the design st

trimming the size and the number of slots. From SE point of view

more smaller slots

• the problem of EM coupling into a rectangular enclosure through

studied based on a multimode approach. The contributions of ind

multiple higher-order modes to the SE of the enclosure have been

• losses can be easily incorporated in the TL model and may be use

effect of electronics

erture-enclosure

pair of aperture-

the SE

age by detuning the

pe of the aperture or

DTD models has been

• EM coupling into a rectangular enclosure with aperture under ap

resonant conditions has been investigated using the TL model. A

enclosure resonances have been found which significantly reduce

• energy transfer into an enclosure may be reduced at the design st

aperture-enclosure resonances by geometrically trimming the sha

enclosure

• good agreement between the results obtained for the TL and the F

obtained

• solution time is the key advantage of the developed model.

ods and Computational

n, M.D. Ganley, A.C.

tion for the Shielding

. on Electromagnetic

tiveness Estimation of

mpatibility Symposium

ode Transmission Line

ures”, 2001 IEEE EMC

702-707,

References:[1] F.M. Tesche, M.V. Ianoz, and T. Karlsson, EMC Analysis Meth

Models, John Wiley & Sons, Inc., New York, 1997

[2] M.P. Robinson, T.M. Benson, C. Christopoulos, J.F. Dawso

Marvin, S.J. Porter, D.W.P. Thomas, “Analytical Formula

Effectiveness of Enclosures with Apertures,” IEEE Trans

Compatibility, vol. 40, no. 3, 1998, pp. 240-247.

[3] I. Belokour, J. LoVetri, and S. Kashyap, “Shielding Effec

Enclosures with Apertures”, 2000 IEEE Electromagnetic Co

Proceedings, pp. 855-860, 2000.

[4] I. Belokour, J. LoVetri, and S. Kashyap, “A Higher-Order M

Model of the Shielding Effectiveness of Enclosures with Apert

International Symposium Proceedings, Montreal, Quebec., pp.

DEVELOPMENT AND INVESTIGATION OF …• Development and investigation of approximate phenomenological models describing and estimating the coupling of EM energy through apertures into

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