EMC/I Simulations with CST MICROSTRIPES · PDF fileEMC/I Simulations with CST MICROSTRIPES ... M. D’Amore et. al, IEEE trans. On EMC, Vol. 42, No. 1, February 2000

1 www.cst.com | European User Group Meeting 2009; © CST 2009; Commercial in Confidence

EMC/I Simulations with

CST MICROSTRIPES™

Paul DuxburySenior Sales and Applications Engineer

CST UK [email protected]

+44 (0)7799 648 044

mailto:[email protected]

2

Introduction

The last few years have seen a significant development in, and

maturing of, modelling software specifically for EMC applications

Such that it is now being seen by many organisations as a vital

part of the electronics design process

CST MICROSTRIPES™ uses the TLM (transmission line matrix)

method for solving Maxwell’s equations

Johns P B & Beurle R L; ‘Numerical Solution of two-dimensional scattering

problems using transmissions-line matrix’, Proc IEE 118, p1203-1208, 1971

This presentation will overview

The TLM technique

Some typical EMC applications

Some of the key features of CST MICROSTRIPES™ which make it

especially suited to EMC modelling

www.cst.com | European User Group Meeting 2009; © CST 2009; Commercial in Confidence

3

Transmission Line Matrix

3D Time domain solution

TLM uses an analogy between transmission line

propagation and wave propagation

Basis functions are pulses traveling along the transmission-

lines and scattering at nodes

All 6 field components are co-located which simplifies the

definition of boundary conditions and improves the

accuracy

Time-domain response can be Fourier transformed giving

wideband high-fidelity frequency-domain results, or

convolved with transient waveforms (pulse train,

lightning, EMP etc.)


4


Boundary conditions are modeled by pulse reflections and

transmissions

Each cell can have different material properties

The TLM grid can be non-uniform enabling cells to be

crowded around areas of detail

Octree-TLM enables complex problems to be solved

efficiently

Wire and circuit models (and other transmission-line

models) are easily integrated into TLM


5


V7V12

V4

V2

V3

V6V11

V10

V8

V9

V1V5

z

y

x

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


6

SAR of 3 Layered Sphere

TLM (thick) and analytic (thin)

results for SAR through a

layered sphere;

70mm radius muscle, 5mm

fat, 3mm skin

TLM (left) and analytic (right)

results for SAR through a

layered sphere at 200MHz

(above) and 1GHz (below)


7

Octree Meshing in TLM

TLM method provides

interface between coarse and

fine cells

Enables localised meshing

around detail

Grid is refined close to

surfaces

Cells are progressively lumped

into bigger cells away from the

surface

This is an automatic process in

CST MICROSTRIPESTM

In many cases the cell count

can drop by over 90% as a

result of the lumping process


8

Octree Meshing in TLM

~95% of the mesh is unnecessary

No Lumping

Cells in

Basic Grid

(k)

Cells in

Solver

Model (k)

Computing

Time (mins)

Required

Memory

(MB)

Manual

Lumping

Automatic

Lumping4346.5

896.7

4326.3

304.6 9

30

38.8

103.8

152 421.34346.5

4346.5


9

Aircraft EMP analysis

Coupling into internal cables

Robotic vehicle shielding

2U server emissions (3m scan)

Automotive control system

emissions (CISPR-25 model)

Card cage ESD analysis

Lightning strike

etc…

Sample EMC / EMI Applications


10

Compact Models In EMC applications, detail in the

geometry can be important

Slots, seams, wires

We could use an extremely fine

mesh to capture the detail but this

would lead to

Long simulation times

High memory requirements

Compact models are a more

efficient approach

Equivalent electrical model of

coupling

Allowing electrically important

but, geometrically small features

to be included in the model

without having to use a very fine

mesh to represent them

Field-Wire

Interactions

Scattering process models

coupling through apertures and

diffusion through thin panels


11

Compact models:

Seams and slots

Vents and screens

Composite panels

Conductive coatings

Absorbers (Ferrite, RAM)

Wires and cables

Sources

Considerable reduction in

computer memory and run-time

Ideal for simulating coupling into

enclosures, cabling, emissions etc…

Compact Models

transfer

impedance


12

Comparison19 in. rack shielding analysis

Solution technique CPU time and RAM

Fine mesh used to capture

seams/vents

30 hours

529 MBytes

Fine mesh with cell-

lumping (octree mesh)

220 minutes

101 MBytes

Coarser mesh using

compact seams/vents

1.5 minutes

13 MBytes


13

Electronics System Emissions

Note; Results

shown are for a

different modelPeak E-field distribution on 3m

radius and height cylinder at 3GHz

E-field distribution at

10GHz – vent leakage

E-field distribution at

3GHz – seam leakage


Vents

Heatsinks

Slots /

Seams

Fans

Enclosure

14

Wire Radius; 1.75mm

Wire Loss; 2/m

Max Freq; 500MHz

Mesh; 20%, +Z 40%

3nS 100nS

1V/m


15

Direct; 126 sec

Indirect; 122 sec


16

CISPR 25 Simulation

The ultimate end-game is a virtual anechoic

chamber CISPR 25 radiated emissions simulation.

Model the ECM, cable harness, load box on the

copper table top in free space.

Ground plane

beyond mesh

Monitor point 1m

from harness

Image courtesy Continental Automotive, USA


17

The cable resonates when its length

is equivalent to an integer number of

half-wavelengths

CISPR 25 Simulation

690 MHz

90 MHz

Adding return paths directly around the

microprocessor reduces the common-

mode current on the PCB and cables

Baseline

With 4 return pins


18

CISPR 25 Simulation

Vertical

polarization

Horizontal

polarization

Counter-intuitively, the vertical polarization is stronger than the

horizontal (interaction between the cable and ground plane causes this)


19

Aim: to measure current induced in test wire

as a result of exciting parallel plate via a wire

injected with a double exponential pulse

(peak current 1400A)

Drive

n w

ire

(d

ou

ble

exp

on

en

tia

l tr

an

sie

nt)

50

Shielded Wire Compact Model

Model courtesy of BAe Systems

Shielded cables are modeled using a compact sub-cell representation.

Details of cable and shield do not need to be meshed.

Shielded cable characterized by a transfer impedance:

Zt = R + jM12

Transfer Impedance Calculator computes voltage coupled to cable at the terminations.

I

VZT = V/I


20

Baseline (Aperture); Current in BNC Screen.

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250

Time (us)

Cu

rren

t A

mp

litu

de

(A)

Cu

rrent in

ca

ble

scre

en

Baseline (Aperture); Voltage on BNC Inner.

-0.5

0

0.5

1

1.5

0 50 100 150 200 250

Time (us)

Ind

uced

Vo

ltag

e (

V)

Modelling Result Measured Result

Voltage o

n

ca

ble

in

ne

rShielded Wire Compact Model

Model courtesy of BAe Systems


21

CST CABLE STUDIO™


22

Current Field Source Excitation

E-field on surface

Surface current


23

EMP Test Problem

Carbon fiber reinforced front panel 70cm size box

M. D’Amore et. al, IEEE trans. On EMC,

Vol. 42, No. 1, February 2000

E(t) = k Eo(e-t/a – e-t/b)

Eo = 50,000 V/m

K = 1.13

a = 200 nS

b = 5 nS


24

EMP Test Problem

Modelled Measured

E F

ield

H F

ield

M. D’Amore et. al, IEEE trans. On EMC,

Vol. 42, No. 1, February 2000


25

Humvee EMP Application

Coax cable current

E field


26

Fighter Aircraft EMPBuild Model TLM Model

Time

Animation of

EMP

Coupling

Transient source used to

model the MIL-STD-464

double-exponential

waveform with peak E

field 50 KV/m

Effect of angle of

incidence and

polarization can be

investigated

Compact slots/seams

defined in the fuselage

Thin film used to model

composite panels

Aim of the analysis is to

predict coupling into

internal cabling


27

Lightning Test Problem

13.2m sized metal box with interchangeable lid and front panel;

Side walls are perfect electrical conductors (PEC)

Top can be PEC or 1.2mm thick Aluminum

Front panel can be closed or contain a slot

Lightning current driven into conductor

Magnetic field calculated inside the box

Lightning conductor

Slot aperture (12 x 0.01)

PML

M. Sarto, IEEE trans. On EMC,

Vol. 43, No. 3, August 2001


28

Simulated Magnetic Field

Lightning

waveform (source)

Curre

nt in

Conducto

r

Diffusion through

walls slows responseHz

Hx

Hy

Al Box

HzHx

Hy

PEC S

ide W

alls,

Al L

id

Magnetic field reduced

with PEC side walls

PEC S

ide W

alls,

Al

Lid

, Slo

tted F

ront

Panel

Faster response

with slot present

Hz

Hx

Hy


29

Current Distribution

100kHz; Diffusion dominates 10 MHz; Slot leakage dominates


30

Fighter Aircraft Lightning Analysis

Surface and wire currents Magnetic field

Nose to tail lightning strike

simulated using MIL-STD-464 A

waveform

(200kA peak current)


31

Ferrite Tile Model

Allows thin ferrite tiles with conductor backing to be modeled

without the need to mesh the tile thickness.

Fully frequency dependant ferrite model.

Validated accuracy for anechoic chamber modeling.


32

PCB Simulation

Complexity:

PCBs often have many layers, thousands of traces and

components

Enclosure may be geometrically complex and contain EMC-

critical detail such as seams, vents, connectors and cabling

Huge disparity in dimensions (um to meters)

Computer requirements:

Memory and solve-time increases with model complexity and

frequency

Analysis needs to be fast enough to influence design process

Impractical to simulate the entire problem in full detail

Replace the complex PCB with an equivalent radiating source,

or Compact Source


33

PCB Simulation


PCB Layout

CST PCB STUDIO™

CST MICROSTRIPES™ or

CST MICROWAVE STUDIO®

34

PCB in Free Space

Electric field

500mm above

the PCB

Radiated

power from

the PCB

Compact Model

>90% quicker


35

PCB in Enclosure

Electric field

3000mm in front

of enclosure

Radiated

power from

the enclosure

Compact Model

>80% quicker


36

Compact source generated from MS near-field scan data

Compact Antenna Source


37

CST MICROSTRIPES™ 2009

Key EMC Technology

Time domain analysis

Transient sources, broadband analysis

Efficient meshing

Octree based, lumped cells

Compact models

Slots, seam, vents, cables, …

Lumped circuits

R, L, C, sources, outputs

Broadband compact source

Output beyond mesh and emissions scans

Ground plane beyond mesh


38

EMC/I Simulations with

CST MICROSTRIPES™

Paul DuxburySenior Sales and Applications Engineer

CST UK [email protected]

+44 (0)7799 648 044


mailto:[email protected]

Documents

EMC/I Simulations with CST MICROSTRIPES · PDF fileEMC/I Simulations with CST MICROSTRIPES ... M. D’Amore et. al, IEEE trans. On EMC, Vol. 42, No. 1, February 2000