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时间:2019-11-28
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1、SolvedwithCOMSOLMultiphysics5.1ModelingofPyramidalAbsorbersforanAnechoicChamberIntroductionInthisexample,amicrowaveabsorberisconstructedfromaninfinite2Darrayofpyramidallossystructures.Pyramidalabsorberswithradiation-absorbentmaterial(RAM)arecommonlyusedinanechoi
2、cchambersforelectromagneticwavemeasurements.Microwaveabsorptionismodeledusingalossymaterialtoimitatetheelectromagneticpropertiesofconductivecarbon-loadedfoam.PerfectlymatchedlayersConductivepyramidalformPortConductivecoatingUnitcellsurroundedbyonthebottomperiodi
3、cconditionsFigure1:Aninfinite2Darrayofpyramidalabsorbersismodeledusingperiodicboundaryconditionsonthesidesofoneunitcell.ModelDefinitionTheinfinite2DarrayofpyramidalstructuresismodeledusingoneunitcellwithFloquet-periodicboundaryconditionsonfoursides,asshowninFigu
4、re1.Thegeometryofoneunitcellconsistsofonepyramidsittingonablockmadeofthesame1
5、MODELINGOFPYRAMIDALABSORBERSFORANANECHOICCHAMBERSolvedwithCOMSOLMultiphysics5.1material.Thereareperfectlymatchedlayers(PMLs)abovethepyramidandtheremainingspacebetweenthepyramidandthePM
6、Lsisfilledwithair.Thepyramidalabsorberismadeofaconductivematerial(σ=0.5S/m).Attheinterfaceoftheconductivematerialandair,theincidentfieldispartiallyreflectedandpartiallytransmittedintothepyramid.Thetransmittedfieldisattenuatedinsideofthelossymaterial.Forangleswit
7、hinaparticularrangeofnormalincidence,thepropagationdirectionofthereflectedfieldisnotbacktowardsthesource,butinsteadtowardsanothersurfaceoftheconductivematerial.Theprocessofpartialreflectionandpartialtransmissionwithsubsequentattenuationisrepeateduntilthefieldrea
8、chesthebaseofthepyramid.Theamplitudeofthefieldatthebaseofthepyramidisdrasticallyreducedandsothereflectionfromtheabsorberatthispointismarginal.TheprocessisillustratedinFigure2.IncidentwaveConductivefoamNoisefromoutsidethechamberisblockedbyahighlyconductivelayerFi
9、gure2:Theincidentwaveispartiallytransmittedintotheconductivefoamwhereitissubsequentlyattenuated.Forangleswithinaparticularrangeofnormalincidence,thereflectedcomponent
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