电磁波在介质中的传播规律

venturecapitalinvestmentguaranteemechanisms,talents,positiveforspecialfunds,playtotheguidingroleoffinancialcapital,leveragingfeatures,evolvingfinancialresources,capital,financialcapital,protectionofsocialcapitalintonewpatterns.3innovationenvironment,optimizingtalent,createagoodatmosphere.Departmentsatalllevelstoputscienceandtechnologyinnovationandtalentworkinginthestrategicpositionofprioritydevelopment,andfullplaytotheguidingroleofGovernment,vigorouslypromotescientificandtechnologicalinnovationandthepreferentialpolicies,mobilizingtheentiresociety'sawarenessofinnovation,stimulatecreativity.Furtheropenservicethegreenchannelfortalenttoprovideefficient,convenient,qualityserviceandallowallkindsoftalentstofocusoninnovation,playtoourstrengths.County-levelaccreditationinrecognitionofworkinatimelymanner,contributingtotalentandrewardingscientificandtechnologicalachievementstoemerge,releasepatentawardsgrants,encouragepatentapplications,socialforcesareencouragedtosetupscienceandtechnologyawards,createanenvironmentconducivetoscientificandtechnologicalprogress,technologicalinnovation,talentandcareerpolicyenvironment,ruleoflaw,marketandsocialenvironment.Comrades,technologicalinnovation,talentisa电磁波在介质中的传播规律电磁波的传播是电磁场理论的重要组成部分。我们只考虑电磁波在各向同性均匀线性介质中传播，分别对电磁波在线性介质和非线性介质中的传播规律进行讨论。1、电磁场的波动方程一般情况下，电磁场的基本方程是麦克斯韦方程，而我们讨论的介质是各向同性均匀线性的，即（0,0j）的情形。麦克斯韦方程组的解既是空间的函数又是时间的函数，而我们只考虑随时间按正弦函数变化的解的形式。对于这种解，其形式可表示成一个与时间无关的复矢量和一个约定时因子tjexp相乘，这里是角频率。在这种约定下，麦克斯韦方程组便可表示成1ΗEj(1)ΕΗj(2)0Ε(3)0Η(4)对方程（1）两边同取旋度，并将式(2)代入便得ΕΕ2（5）利用如下矢量拉普拉斯算子定义以及方程（3）ΕΕΕ2（6）方程（5）式变为2022ΕΕk（7）k（8）类似地，可得Β所满足的方程为022ΒΒk（9）方程（7）和（9）式称为亥姆霍兹（Helmholtz）方程，是电磁场的波动方程。venturecapitalinvestmentguaranteemechanisms,talents,positiveforspecialfunds,playtotheguidingroleoffinancialcapital,leveragingfeatures,evolvingfinancialresources,capital,financialcapital,protectionofsocialcapitalintonewpatterns.3innovationenvironment,optimizingtalent,createagoodatmosphere.Departmentsatalllevelstoputscienceandtechnologyinnovationandtalentworkinginthestrategicpositionofprioritydevelopment,andfullplaytotheguidingroleofGovernment,vigorouslypromotescientificandtechnologicalinnovationandthepreferentialpolicies,mobilizingtheentiresociety'sawarenessofinnovation,stimulatecreativity.Furtheropenservicethegreenchannelfortalenttoprovideefficient,convenient,qualityserviceandallowallkindsoftalentstofocusoninnovation,playtoourstrengths.County-levelaccreditationinrecognitionofworkinatimelymanner,contributingtotalentandrewardingscientificandtechnologicalachievementstoemerge,releasepatentawardsgrants,encouragepatentapplications,socialforcesareencouragedtosetupscienceandtechnologyawards,createanenvironmentconducivetoscientificandtechnologicalprogress,technologicalinnovation,talentandcareerpolicyenvironment,ruleoflaw,marketandsocialenvironment.Comrades,technologicalinnovation,talentisa2、平面波解一般的电磁波总可用傅里叶分析方法展开成一系列。单色平面波的叠加。所以，对单色平面波的研究具有重要的理论和实际意义。假定波动方程（7）和（8）式的单色平面波的复式量解为3rkΕΕtjexp0（10）rkΒΒtjexp0（11）式中0Ε,0Β分别为Ε,Β振幅，为圆频率，k为波矢量（即电磁波的传播方向）。tkxjexp代表波动的相位因子。为了描述均匀平面波的相位在空间的变化快慢，在此引入相速的概念，即平面波等相位的传播速度。很显然等相位面由下面方程决定1constkrt（12）方程（12）两边对时间t求导可得kdtdrv(13)由式（8）可知1v（14）将（10）和（11）式代入我们上面给出的麦克斯韦方程组可得300ΒkΕ（15）0201ΕkΒv（16）00Εk（17）00Βk（18）由（17）和(18)可以看出，介质中传播的电磁波是横波，电场与磁场都与传播方向垂直；venturecapitalinvestmentguaranteemechanisms,talents,positiveforspecialfunds,playtotheguidingroleoffinancialcapital,leveragingfeatures,evolvingfinancialresources,capital,financialcapital,protectionofsocialcapitalintonewpatterns.3innovationenvironment,optimizingtalent,createagoodatmosphere.Departmentsatalllevelstoputscienceandtechnologyinnovationandtalentworkinginthestrategicpositionofprioritydevelopment,andfullplaytotheguidingroleofGovernment,vigorouslypromotescientificandtechnologicalinnovationandthepreferentialpolicies,mobilizingtheentiresociety'sawarenessofinnovation,stimulatecreativity.Furtheropenservicethegreenchannelfortalenttoprovideefficient,convenient,qualityserviceandallowallkindsoftalentstofocusoninnovation,playtoourstrengths.County-levelaccreditationinrecognitionofworkinatimelymanner,contributingtotalentandrewardingscientificandtechnologicalachievementstoemerge,releasepatentawardsgrants,encouragepatentapplications,socialforcesareencouragedtosetupscienceandtechnologyawards,createanenvironmentconducivetoscientificandtechnologicalprogress,technologicalinnovation,talentandcareerpolicyenvironment,ruleoflaw,marketandsocialenvironment.Comrades,technologicalinnovation,talentisa由（15）和（16）式可知：0Ε，0Β与k三者相互垂直，且满足右手螺旋关系。3、电磁波在线性介质中的传播1电磁波在线性介质中的传播，即电介质参数和磁导率都为实数的波传播情况。由关系式（8）可知，波数k必为实数。根据平面波解形式（10）易知，平面电磁波在线性介质中传播，只有相位发生变化，无幅值变化。将式（15）写成ΗΕk（19）其中k。而且的单位是，故称为波阻抗。其物理意义是垂直于传播方向平面上的电场和磁场的比值。在线性介质中，波阻抗为实数，也就是纯电阻，所以电场和磁场同相。4、电磁波在非线性介质中的传播1实际中见到的非线性介质是电介质参数为复数的情形，即'j，譬如海水、湿地。通常这种介质的损耗是由电导率引起，故又有。根据关系式（8）有2/1''1jk（20）将复数k写成jk（21）由式（20）不难推出2/12'1'12（22）2/12''112