參考文稿成果

CST–COMPUTERSIMULATIONTECHNOLOGY|w

ModellingThinMaterialsinCSTSTUDIOSUITE2012

LossyMetalOhmicSheets

TabulatedSurfaceImpedanceThinPanel

VariousMaterialTypes

Materialtypes Availableinwhichsolvers?

*

FIT TLM

*Apartfrom“LossyMetal”,only

availablefortetrahedralmesh.

SurfaceImpedanceMaterials

Inprincipleaclassicaldispersivematerialcouldbeusedtomodelthesematerials.

However,anexcessivelyfinemeshmightbeneeded:

iftheobjectmadeofthatmaterialistoothin

ifthepenetrationdepthofthefieldintotheobjectisvery

small

ifthematerialconsistsofseveralrelativelythinlayers.

Thesurfaceimpedancemodelisawaytoavoidaveryfinemeshinsidethematerial.Useoneofthesematerialtypeswhenevertheskindepthorthematerial’sthicknessistoosmalltomodelin3D.

PrincipleofSurfaceImpedanceMaterials

AsurfaceimpedanceformulationrelatesthetangentialEandHfieldsatthesurfaceofamaterial.

Thefieldinsidethevolumeenclosedbythesurfaceimpedanceisnotcomputed(itisactuallyzero).

k y

Hy

Ez

x

Zs=Ez/Hy

z

k

y

x

Hy1

Hy2

Ez1

z

Ez2

Zt=Ez2/Hy1

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ExtensionoftheSurfaceImpedanceModel:Transferimpedance

Atransferimpedance(Zt)modelrelatestheE-fieldononesideofthematerialsheettotheH-fieldontheotherside;thinpanelmodelusesbothZsandZt

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Transparency

Somematerialtypesallowwavesto“passthrough”themiftheobjectisinfiniythin.Forasurfaceimpedancematerialthismeansthattheelectricfieldonbothsidesofthematerialisthesame.

Lossymetal;corrugatedwall:alwaysopaque

Ohmicsheet:transparentifinfini ythin(i.e.thickness=0);opaqueiftheobjecthasavolume

Surfaceimpedance:user’schoiceifinfini ythin;

opaqueiftheobjecthasavolume

Thinpanel:transparent(hastobeinfini ythin)

CoatedMaterials

3D(thick)objectofcertainmaterialscanhaveacoating

Thesurfaceimpedanceoftheoriginalmaterialisyticallytransformedtotakeintoaccountthe

parametersofthecoatinglayers.

Coatinglayers:“Normal”typematerial,canbedispersive

Theresultisanopaquesurfaceimpedanceobject(transparentonlyforinfini ythinOhmicsheet).

OhmicSheet

Useitifaconstantsurfaceimpedanceoverthewholefrequencyrangeisneeded(inthetransientsolverafirst-ordermodelisused).

Typicalapplications:

ICsimulation(thematerialparametersareoftendirectlygiveninOhmspersquare)

Realizinganon-Cartesianboundaryinthefrequency

solver(filleverythingunwantedwithanOhmicsheetmaterialwhoseinteriorisnotmeshed)

TabulatedSurfaceImpedance

Usethisifthesurfaceimpedanceisstronglyfrequency-dependent(inthetransientsolverafittingofuptoorder10isused).

Typicalapplication:

Lossylayersusedtoabsorborattenuatean ingwavewhicharetoothintobemodelledin3D

CoatedMaterial

Usethismodelforthinabsorbinglayers(dielectrics)cedonmetallicobjects,ifthelayersaretoothintobemodelledin3D,e.g.fordielectric-coatedmetals.

Typicalapplication:

Coating(e.g.RAM)onthesurfaceofanairne

SurfaceModelsforMetalsAccurateatDC

Lossymetalisonlyaccurateathighfrequencies.

ForaccurateDCvalues,onecouldusea“TabulatedSurfaceImpedance”modelwithappropriaow-frequencyandhigh-frequencytabulatedvalues.

ThemacroMaterialsCreateTabulatedSurfaceImpedanceMaterialcanbeusedforthis.

Moreover,itallowsthedefinitionofametalliccoating

(the“CoatedMaterial”typeonlyallowsdielectriccoatings)

Macro:TabulatedSurfaceImpedance

Surfaceimpedanceformultilayeredstructures

Surfaceroughness

Causalityen ment

Example(SurfaceRoughnessRequired)

50mmlong

striplinemodel

FR4dielectricsubstrate–εr=3.5,tgδ=0.06

Summary

Metalwithlosses:“Lossymetal”

AccurateatDC:macro

Thinlossydielectrics(alsouser-definedmetals)

Frequencyindependent:Ohmicsheet

Dispersive:tabulatedsurfaceimpedance

Coatingonmetallicobject