电磁场与电磁波第17讲时谐场概要.ppt

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1、FieldandWaveElectromagnetic电磁场与电磁波第17讲11.Faraday’sLawofElectromagneticInductionReview22.Maxwell’sEquations3.ElectromagneticBoundaryConditionsTheintegralformThedifferentialformSignificanceFaraday’slaw(电磁感应定律)Ampere’scircuitallaw(全电流定律)Gauss’slaw(高斯定理)Noisolatedmagneticcharge(磁通连续性原理)34.PotentialFun

2、ctions5.WaveEquationsandTheirSolutions4Maxwell’sequationsandalltheequationsderivedfromthemsofarinthischapterholdforelectromagneticquantitieswithanarbitrarytime-dependence(时间任意相关).Theactualtypeoftimefunctionsthatthefieldquantitiesassumedependson(取决于)thesource(源)functionsandJ.Inengineering,oneofthe

3、mostimportantcasesoftime-varyingelectromagneticfieldsisthetime-harmonic(sinusoidal)field(时谐场、正弦场).Inthistypeoffield,theexcitationsourcevariessinusoidallyintimewithasinglefrequency(单一频率).Inalinearsystem(线性系统),asinusoidallyvaryingsourcegeneratesfieldsthatalsovarysinusoidallyintimeatallpointsinthesys

4、tem(正弦变化的源产生正弦变化的场).1)whatisTime-HarmonicFields3.Time-HarmonicFields52)讨论时谐场（正弦信号）的原因Whenfieldsareexaminedinthismanner,thereisnolossingeneralityas(a)Theyareeasytogenerate(b)anytime-varyingperiodicfunctioncanberepresentedbyaFourierseriesintermsofsinusoidalfunctions(c)theprincipleofsuperpositioncanb

5、eappliedunderlinearconditions.Inotherwords,wecanobtainthecompleteresponseoftimevaryingperiodicfieldsbyusinglinearcombinationsofmonochromaticresponses（a）正弦信号容易产生，50Hz交流电，通信的载波都是正弦信号（b）从信号分析的角度来看，正弦信号是一种简单基本的信号。正弦信号进行各种运算（加减微分积分后仍为同频率正弦信号）（c）傅立叶分析：任意周期信号分解为不同频率的正弦之和（d）线性系统的叠加原理63.1电路中的相量表达式Incircuit

6、theory,youhavealreadyusedthephasornotation(相量)torepresentvoltagesandcurrentsvaryingsinusoidallyintime(1)Instantaneous(time-dependent)expressionofasinusoidalscalarquantity(瞬时值）三角函数表达式3Parameters:angularfrequency:amplitude:Imphase：(2)复数的表示xjyP（x,y）复平面上一点P7(3)正弦表达式和相量表达式的对应关系相量的模正弦量的幅值初位相复角频率是已知？频率

7、相量乘以ejt，再取实部8EXAMPLE7-6P337-33893.2Time-harmonicElectromagneticsFieldvectorsthatvarywithspacecoordinatesandaresinusoidalfunctionsoftimecansimilarlyberepresentedbyvectorphasors(矢量相量)thatdependonspacecoordinatesbu