IEEE Dallas EMC Society

David Johns

System Level EMC Simulation Using the TLM Method

What is FLO/EMC…?

The first electromagnetic field simulator developed specifically for system-level EMC design in the electronics industry

Enables EMC problems to be identified and managed in the early stages of design

Good for investigating radiated & conducted emissions, immunity (susceptibility), ESD and crosstalk problems: Enclosures & EMI shields Interfaces between boards and chassis Cables and EMI filters Unintentional antennas! (heat sinks etc.)

Based on the 3D Transmission-Line Matrix (TLM) Method

TLM Method

3D space-volume divided into nodes (10th wavelength) Each node is a 12-port transmission-line junction Scattering at the nodes models coupling between E and H fields Transient E and H fields are calculated from combinations of voltages

and currents on the transmission lines Spectrum found by FFT

V8

V9

V11

V10

V4

V2

V3

V6

V12 V7

V1 V5

X

YZ

Ey= ½ (V3i + V4

i + V8i + V11

i ) / Y

TLM Coupling Matrix

YX ZY XY ZX YZ XZ YZ

ZX ZY XZ XY YX

1 2 3 4 5 6 7 8 9 10 11 12

YX 1 1 1 1 -1

ZY 2 1 1 -1 1

XY 3 1 1 1 -1

ZX 4 1 1 -1 1

YZ 5 1 1 -1 1

XZ 6 1 1 1 -1

YZ 7 -1 1 1 1

ZX 8 1 -1 1 1

ZY 9 1 -1 1 1

XZ 10 -1 1 1 1

XY 11 -1 1 1 1

YX 12 1 -1 1 1

S = ½

Reflected Pulses Vr

k+1

Incident Pulses Vi

k

Ey= ½ (V3i + V4

i + V8i + V11

i ) / w

Wave Propagation, Time 0

1

1

1

1

Wave Propagation, Time 1

-0.5

-0.5

-0.5

-0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

Wave Propagation, Time 2

-0.5

-0.5

-0.5

-0.5

0.5

0.25

0.25

0.5

0.50.5

0.25

0.5

0.25

0.5

0.25

-0.25

0.25

0.25-0.25

0.25

0.25

-0.25

0.25

-0.25

0.25

0.25

0.5

Wave Propagation, Time 3

0.25

0.25

0.25

0.25

0.25

-0.25

0.125

0.25

-0.25

0.375

0.25

-0.25

0.25

-0.25

0.375-0.125 0.375

0.375

0.3750.375

0.375

0.3750.375

0.375

0.375

0.375

0.375

0.375

0.3750.375

0.125

0.125

0.1250.125

0.125

0.125

0.125

-0.125

-0.125

-0.125-0.125

-0.125

-0.125

-0.125

0.125

0.125

0.1250.125-0.125

-0.125

-0.125

-0.125

-0.375

-0.375-0.375

-0.375

-0.375 -0.375

-0.375

-0.375

Complexity of EMC Analysis

Compact vent model

seamsair vents

Accurate modeling requires geometric detailA long narrow seam may be a good antenna!Meshing the detail is computationally impractical

connectors

FLO/EMC Smart PartsTLM method uses a TL-Matrix to model fields.Other TL’s & lumped-circuit models can be connected

into the matrix.Arrays of small holes are often necessary to provide

adequate thermal ventilation/cooling.Apertures increase emissions and decrease shielding

effectiveness of the box.Low-frequency fields are evanescent near the apertures.Extremely fine grid would be required to model the

exponential decay.FLO/EMC overcomes this difficulty by inserting a “smart

part” into the grid.

Air vent smart part

L models the current flow along the edges of the apertures C models the electric field stored inside the apertures.

For a thin panel TEM transmission can be modelled by a shunt inductor. L is like a short at DC, but allows high freq. transmission.

For a thick panel the additional electric field inside the aperture can be modelled by a shunt capacitor

TEM

Transmission dependence on aperture shape and size, coverage and depth – empirical results

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0

0.1

0.2

0.3

0.4

0.5

circular aperture array

square aperture array

Tra

nsm

issi

on c

oeffi

cien

t - T

Coverage

0.0 0.5 1.0 1.5 2.00.0

0.1

0.2

0.3

0.4

0.5

circular aperture array

square aperture array

Tra

nsm

issi

on c

oeffi

cien

t - T

Perforation depth / mm

Fine TLM mesh of single aperture used to calculate dependence of Transmission on aperture shape and size, coverage and depth Fit L,C air vent parameters to the Transmission results at two frequencies - 10% and 80% of aperture cut-off frequency

Air Vent Implementation

plane of screen

inductive short (vertical polarization)

inductive short (horizontal polarization)

TLM nodeTLM node

Inductor modelled by short-circuit transmission line

+ + +2Vli

Yl

V to ta l

2Vri

YrYs

2Vsi

Yo

2Voi+

a

iototal

ro

istotal

rs

irtotal

rr

iltotal

rl

VVV

VVV

VVV

VVV

osrl

oios

isr

irl

il

total YYYY

YVYVYVYVV

2

Capacitor modelled by open-circuit transmission line

1D propagation through an array of circular apertures (depth equal to diameter)

0 10 20 30 40 50 60 700.00

0.02

0.04

0.06

0.08

0.10

0.12

single L modelair-vent modelfine TLM mesh

|Ey|

in o

utpu

t poi

nt /

V/m

frequency / GHz

Validation - Plane Wave

The fine TLM mesh and air vent model give the same results at 10% and 80% of aperture cut-off frequency

Validation - Emission

r

p

t

a = 50 mmb = 20 mmc = 40 mmd = 10 mm

r = 10.0 mmp = 5.0 mmt = 1.65 mmN = 252

c

a

lossy material

.

.d

excitation

b

xz

y

lon g -w ire feed[M.Li et al,’EMI…’,IEEE Trans EMC, Vol. 42, No. 3, p265,2000]

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2-60

-50

-40

-30

-20

-10

0

10

20

30

single L model

air-vent model

measurements

|E| a

t 3m

aw

ay, d

BmV

/m

frequency / GHz

Run time on Dual Pentium Xeon with 3 GHz clock rateAir vent model

3 min

Enclosure with thick walls

r

p

t

a = 100 mmb = 80 mmc = 15 mm

r = 5.08 mmp = 0.69 mmt = 5.20 mmN = 45

y

b

c

...excitation

z

x

a.

output point

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

single L modelair-vent modelfine TLM mesh

e:ou

tput

poi

nt /

dBV

/m

frequency / GHz

Run time on Dual Xeon with 3 GHz clock rate

Fine TLM mesh Air vent model

2.5 hours 4 min

Enclosure with vents & slots

y

b

c

.

.

.excitation

z

x

a

t

w

a = 50 mmb = 20 mmc = 40 mm

= 94.92 mmw = 0.69 mmt = 0.20 mm

r

p

t

r = 5.08 mmp = 0.69 mmt = 0.20 mmN = 45

Air vents and slots

Run time on Dual Xeon with 3 GHz clock

fine TLM mesh compact models

2.5 hours 3 min

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0-60

-50

-40

-30

-20

-10

0

10

20

30

compact modelsfine TLM meshe:

fron

t1 /

dB

V/m

frequency / GHz

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0-80

-70

-60

-50

-40

-30

-20

-10

0

10

compact modelsfine TLM meshe:

fron

t /

dBV

/m

frequency / GHz

3m from air vent 3m from slot

Multi-Wire Smart Part

Compact vent model

Multi-conductor TL models of wires are connected into the TLM grid

Full coupling between wires and fieldsSupports splits, bends, multi-way connections,

circuit terminations and ports

connector pins

cable

Near Field Scan Smart Part

Emissions

Pre-determined near-field scans over entire boards or regions/components can be imported and applied as distributed frequency-dependent (time-varying) sources

Ideal for PCB with 1 or 2 layers where radiation from “exposed” nets may be important

TLM References

1. Johns P. B. & Beurle R. L., ‘ Numerical Solution of 2-Dimensional Scattering Problems Using a Transmission-Line Matrix’, Proc. IEE, Vol. 118, No. 9, Sept 1971. 

2. Akhtarzad, S. and Johns, P. B., ‘The solution of Maxwell’s equations in three space dimensions and time by the TLM method of numerical analysis’, Proceedings IEE 122, 12, p.1344-1348, December 1975. 

3. Johns P. B., ‘A symmetrical condensed node for the TLM method’, IEEE Trans. Microwave Theory and Techniques, Vol. MTT-35, No. 4, pp. 370-377, 1987.

4. Christopoulos C., ‘The Transmission-Line Modeling Method: TLM’, IEEE Press and Oxford University Press, 1995. A volume in the IEEE/OUP Series on Electromagnetic Wave Theory ISBN 0-7803-1017-9

If you have any questions or comments, we welcome your feedback !

Please visit the FLO/EMC web site at www.floemc.com and email us at emsupport@flomerics.com

Flomerics Inc.257 Turnpike Road, Suite 100Southborough MA 01772

Tel: (508) 357 2012

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Tel: (512) 420 9273

Flomerics Inc.

410 South Melrose Drive, Suite 102,

Vista, CA 92083

Tel: (760) 643 4028

Flomerics Inc. 4699 Old Ironsides Drive - #390 Santa Clara, CA 95054-1860

Tel:(408) 562-9100