电磁场与电磁波第19讲极化导电媒质ppt课件.ppt

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1、FieldandWaveElectromagnetic电磁场与电磁波第19讲1作业情况1班：人合计：人情况:21.PlaneWavesinLosslessMedia理想介质planewave;uniformplanewaveReview3zHyEx41.1transverseelectromagneticwaves横电磁波5MaintopicPlaneElectromagneticWaves1.PlaneWavesinLossyMedia(导电媒质中的平面波)2.PolarizationofPlaneWaves(平面波的极化)6Supposethemedi

2、umislinear,homogeneous,andisotropic,fromMaxwell’sequationwefindWehave2.PlaneWavesinLossyMedia7Insimple,nonconductingsource-freemediumcharacterizedby=0,J=0,=0,thetime-harmonic:WehaveHomogeneousvectorHelmholtz’sequations.8Insimple,conductingsource-freemediumcharacterizedby=0,0,

3、thetime-harmonic:WehaveHomogeneousvectorHelmholtz’sequations.with9Inasource-freelossymedium(=0,0),thehomogeneousvectorHelmholtz’sequationtobesolvedisThederivationsanddiscussionspertainingtoplanewavesinalossless无耗mediumcanbemodifiedtoapplytowavepropagationinalossy有耗mediumbysimpl

4、yreplacingkwithkc.However,inanefforttoconformwiththeconventionalnotationusedintransmission-linetheory,itiscustomarytodefineapropagationconstant,,suchthatwithWewrite10Whereandaretherealandimaginarypartsof,botharepositivequantities.respectively.Foralosslessmedium,=0,=k=()1/

5、2.Withthehelpof,theHelmholtz’sequationbecomesIfwehaveassumedthatthewaveislinearlypolarizedinthex-direction.Thesolutionoftheequation,representingauniformplanewavepropagatinginthe+z-direction,is2.1Thephysicalsignificanceofand.11Thefirstfactor,e-z,decreasesaszincreasesandthusisan

6、attenuationfactor,andiscalledanattenuationconstant(衰减常数).TheSIunitoftheattenuationconstantisneperpermeter(Np/m).Thesecondfactor,e-jz,isaphasefactor,iscalledaphaseconstant(相位常数)andisexpressedinradianspermeter(rad/m).Thephaseconstantexpressestheamountofphaseshiftthatoccursasthewa

7、vetravelsonemeter.2.2low-lossdielectrics低损耗电介质(’’<<’,<<)12ExHyzWeobtaintheattenuationconstant衰减常数andthephaseconstant相位常数Theintrinsicimpedance本征阻抗ofalow-lossdielectricisacomplexquantity复数.SincetheintrinsicimpedanceistheratioofExandHyforauniformplanewave,theelectricandmagneticf

8、ieldintensitiesinalossydielectric