RuguiYangHigherEducationPressHigherEducationElectronicandVideoPressElectromagneticFieldsandWavesThephysicalunderstandingisemphasizedinsteadofthemathematicalderivation.Classhourdistribution（Classhours64：Lecture60，Spare:4）Vectoranalysis4Electrostaticfields7Boundary-valueproblems4Steadycurrentfields3Steadymagneticfields6EMinduction3Time-varyingEMfields7PlaneEMwaves10

GuidedEMwaves8PrinciplesofEMradiation8ElectricField&MagneticField電場和磁場Preface前言

Thefieldsproducedbythemovingchargesortheelectriccurrentsbehavesasthefunctionoftheforceactingonthemagnetandtheconductor

carryingcurrentsarecalledmagneticfields.運(yùn)動(dòng)電荷或電流產(chǎn)生的場表現(xiàn)為對于磁鐵和載流導(dǎo)體有力的作用，這種物質(zhì)稱為磁場

Thefieldsproducedbythestaticchargesbehavesasthefunctionoftheforceactingonthecharge,anditiscalledtheelectricfields.靜止電荷產(chǎn)生的場表現(xiàn)為對于帶電體有力的作用，這種場稱為電場Theelectricfieldsunchangingwithtimearecalledelectrostaticfields.不隨時(shí)間變化的電場稱為靜電場Themagneticfieldsunchangingwithtimearecalledsteadymagneticfields.不隨時(shí)間變化的磁場稱為恒定磁場。

Ifthechargeandthecurrent

vary

withtime,theelectricfieldandmagneticfieldtheyproducewillbe

functionsof

time.如果電荷及電流均隨時(shí)間改變，它們產(chǎn)生的電場及磁場也是隨時(shí)變化的ElectromagneticWave電磁波

Electrostaticfieldandsteadymagneticfieldareindependentofeachother,andmaybeinvestigatedseparately.靜電場與恒定磁場相互無關(guān)、彼此獨(dú)立，可以分別進(jìn)行研究

The

interaction

betweentime-varyingelectricfieldandtime-varyingmagneticfieldresultsinan

electromagneticwave

inspace.時(shí)變電場與時(shí)變磁場之間的相互轉(zhuǎn)化作用，在空間形成了電磁波

Time-varyingelectricfieldandmagneticfieldmust

co-existandhavedefiniterelation

toeachother,leadingtoatime-varying

electromagneticfield.時(shí)變的電場與時(shí)變的磁場可以相互轉(zhuǎn)化，兩者不可分割，它們構(gòu)成統(tǒng)一的時(shí)變電磁場Entity物質(zhì)屬性

The

existence

andtransmission

ofelectromagneticwavesneed

notrelyon

anymedium.Specifically,whenanelectromagneticwavetravelsthrougha

vacuum,itissaidtopropagatein“freespace”.

電磁場與電磁波是一種物質(zhì)，它的存在和傳播無需依賴于任何媒質(zhì)。在沒有物質(zhì)存在的真空環(huán)境中，電磁場與電磁波的存在和傳播會(huì)感到更加“自由”。因此對于電磁場與電磁波來說，真空環(huán)境通常被稱為“自由空間”。

Electromagneticfieldsandwavesareinvisible

(exceptforvisiblelight),theirexistencecanbeinferredfromthe

energy

andmomentum

theycarry.

電磁場與電磁波雖然不能親眼所見，但是客觀存在的一種物質(zhì)，因?yàn)樗哂形镔|(zhì)的兩種重要屬性：能量和質(zhì)量。但是，電磁場與電磁波的質(zhì)量極其微小，因此，通常僅研究電磁場與電磁波的能量特性。Forcesandenergyarethemostimportant.

Inthepresenceofmatter,anelectromagneticfieldgivesrisetopolarizationandmagnetization,andtheyinturnleadtosecondaryfieldswhichwillmodifytheoriginalfielddistribution.Thisistheinteractionbetweenthefieldandmatters.

當(dāng)空間存在媒質(zhì)時(shí)，在電磁場的作用下媒質(zhì)中會(huì)發(fā)生極化與磁化現(xiàn)象，結(jié)果在媒質(zhì)中又產(chǎn)生二次電場及磁場，從而改變了媒質(zhì)中原先的場分布，這就是場與媒質(zhì)的相互作用現(xiàn)象。Field&Matter場與媒質(zhì)Fortheconvenienceofstudy,wefirstintroduceelectro-magneticfieldsinfreespace,afterwhichtheelectromagneticfieldinmatterwillbediscussed.

為了研究方便起見，我們先介紹真空中的電磁場，然后再討論媒質(zhì)中的電磁場。

Electricchargesandcurrentsaretheonlysourcesforproducingelectromagneticfields.Uptonow,nomagneticchargeormagneticcurrenthasbeenfoundtoexistinnature.電荷及電流是產(chǎn)生電磁場惟一的源。至今，人們尚未發(fā)現(xiàn)自然界中存在磁荷及磁流。Field&Source場與源Investigationontherelationbetweenthefieldanditssourceisafundamentalsubject.Wewillintroduceanumberofmathematicalequationstodescribetherelationshipbetweenthefieldandthesource,aswellasbetweenthefieldandthemedia.研究場與源的關(guān)系是電磁理論的基本問題之一。我們將要詳述場與源，以及場與媒質(zhì)之間的關(guān)系，并且給予嚴(yán)格的數(shù)學(xué)描述。

Nevertheless,theintroductionofmagneticchargesandcurrentsintheanalysisofelectromagneticfieldscanprovetobebeneficialsometimes,

althoughthesemustbetreatedasfictitiousentities.然而，有時(shí)引入磁荷及磁流的概念是十分有益的，但是，它們僅是假想的。History歷史的回顧

Theabilityofapieceofamber琥珀

toattractsmallitemsafterithadbeenrubbedwasdiscoveredbytheGreeksin600B.C.Theattractiveforcebetweenamagnetandiron鐵

wasnotedbytheChinesein300B.C.公元前600年希臘人發(fā)現(xiàn)了摩擦后的琥珀能夠吸引微小物體；公元前300年我國發(fā)現(xiàn)了磁石吸鐵的現(xiàn)象；

In1785,FrenchscientistCharlesAugustindeCoulomb(1736—1806)discoveredCoulomb’slaw(1785年法國科學(xué)家?guī)靵觯?736－1806）通過實(shí)驗(yàn)創(chuàng)建了著名的庫侖定律),anditgivestherelationshipbetweentheforceexperiencedbytwosmallchargedobjectsandthedistancebetweenthem.

Earlyinthefirstcentury,thecompasswasinventedanditwasamongthefourgreatinventionsinancientChina.Thereafter,themagneticfieldoftheearthwasdiscovered.

In1820,DanishscientistHansChristianOersted(1777—1851)discoveredthemagneticfieldproducedbyanelectriccurrent.Inthesameyear,FrenchscientistAndreMarieAmpere安德烈.瑪麗.安培(1775—1836)determinedtheforcebetweentwoelectriccurrents.1820年丹麥人奧斯特（1777－1851）發(fā)現(xiàn)了電流產(chǎn)生的磁場，同年法國科學(xué)家安培（1775－1836）計(jì)算了兩個(gè)電流之間的作用力。In1831,BritishscientistMichaelFaraday(1791-1867)discoveredthephenomenonofelectromagneticinductionandputforththelawofelectromagneticinduction,whichstatesthatatime-varying

magneticfieldmustgiverisetoanelectricfield.

1831年英國科學(xué)家法拉第（1791－1867）發(fā)現(xiàn)電磁感應(yīng)現(xiàn)象，創(chuàng)建了電磁感應(yīng)定律，說明時(shí)變磁場可以產(chǎn)生時(shí)變電場。In1873,Britishscientist

JamesClerkMaxwell(1831—1879)

postulatedthe

displacementcurrent,whichprovidedthelinkbetweenatime-varyingelectricfieldandamagneticfield.Heputonafirmmathematicalfoundationthelawsgoverninganelectromagneticfield.TheyareknowntodayasthefamousMaxwell’sequations.1873年英國科學(xué)家麥克斯韋（1831－1879）提出了位移電流的假設(shè)，認(rèn)為時(shí)變電場可以產(chǎn)生時(shí)變磁場，并以嚴(yán)格數(shù)學(xué)方程描述了電磁場與波應(yīng)該遵循的統(tǒng)一規(guī)律，這就是著名的麥克斯韋方程。AGreatInnovation重大突破Theseequationsstatethatatime-varyingelectricfieldproducestime-varyingmagneticfieldandviceversa.Maxwellfurtherpredictedtheexistenceofelectromagneticwaves,whichwasdemonstratedin1887bytheexperimentconductedbyGermanphysicistHeinrichRudolphHertz(1875—1894).該方程說明了時(shí)變電場可以產(chǎn)生時(shí)變磁場，同時(shí)又表明時(shí)變磁場可以產(chǎn)生時(shí)變電場，因此麥克斯韋預(yù)言電磁波的存在，后來在1887年被德國物理學(xué)家赫茲（1857－1894）的實(shí)驗(yàn)證實(shí)。Aroundtheendofthe19thcentury,PopovinRussiaandMarconiinItalyinventedthetechnologytotransmitinformationusingelectro-magneticwaves.

俄國的波波夫及意大利的馬可尼于19世紀(jì)末先后發(fā)明了用電磁波作為媒體傳輸信息的技術(shù)。

Applications電磁場與波的應(yīng)用

Modernwirelesscommunications,broadcasting,radar,remotecontrol,microwavesensing,wirelessnetworksandlocalareanetworks,satellitepositioning,opticalcommunicationsandotherinformationtechnologies,allofthemuseelectromagneticwavestotransmitinformation.當(dāng)今的無線通信、廣播、雷達(dá)、遙控遙測、微波遙感、無線因特網(wǎng)、無線局域網(wǎng)、衛(wèi)星定位以及光纖通信等信息技術(shù)都是利用電磁波作為媒介傳輸信息的。

Electrostaticxerography,cleaning,andspraying,areallbasedontheactionofelectricforces.靜電復(fù)印、靜電除塵以及靜電噴漆等技術(shù)都是基于靜電場對于帶電粒子具有力的作用。

Electromagnets,maglevbearings,andmaglevvehicles,allofthembeingbasedontheactionofmagneticforces.電磁鐵、磁懸浮軸承以及磁懸浮列車等，都是利用磁場力的作用。

TheFirstHTSMaglevVehicle世界首輛載人高溫超導(dǎo)磁懸浮試驗(yàn)車AppliedSuperconductivityR&DCenter,SWJTUStable!Stable!AMaglevVehicleinShanghai上海磁懸浮列車StealthBomber-B2irStealthFighterF-117X-47StereoscopicFilm

GlobalPositioningSystemGPSThewideapplicationsofthesenewtechnologiesfurtherenhancethedevelopmentofelectromagnetictheory.Newelectromagneticmaterialsarediscovered,andnewmethodstoanalyzeandcomputeelectromagneticproblemsarecreated.以上新技術(shù)的廣泛應(yīng)用又促進(jìn)了電磁理論的發(fā)展。由此創(chuàng)建了很多分析電磁場與波的新方法，研制了很多電磁性能優(yōu)越的新材料。Promotion&Development相互促進(jìn)，共同發(fā)展Especially,theavailabilityofhighperformanceandhighspeedcomputerswithlargememorycapacitynotonlymadethecalculationsencounteredinobtainingthesolutionstomanyproblemsinelectro-magneticspossible,butalsogaverisetonewmethodstocomputeelectromagneticfieldsandwaves.Thisgavebirthtocomputationalelectromagnetics.特別是隨著大容量的高性能及高速度計(jì)算機(jī)出現(xiàn)，不但解決了很多電磁理論的計(jì)算問題，同時(shí)也萌生了計(jì)算電磁場與波的新方法，從而形成計(jì)算電磁學(xué)的新學(xué)科，它是當(dāng)今電磁學(xué)的重要分支。Units電磁單位TheS.I.systemofunitsisemployedinthisbook.Inelectro-magnetics,thefourbasicquantitiesarelength(inmeters),mass(inkilograms),time(inseconds),andelec