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1、ContemporaryPhysics,January-February2004,volume45,number3,pages191-202NegativerefractionJ.B.PENDRYLightbendsthewrongwayinmaterialswherebothεandμarenegativeaswaspointedoutin1968,buttheabsenceofnaturalmaterialswiththispropertyledtoneglectofthesubjectuntil1999whenitwass
2、hownhowtomakeartificialmaterials,metamaterials,withnegativeμ.Therapidadvanceofthesubjectsincethatdate,bothintheoryandexperiment,isreflectedintheexponentialgrowthofpublicationsnowatthe200peryearlevelandstillgrowing.Thisinterestisexplainedbythesuddenavailabilityofaqual
3、itativelydifferentclassofelectromagneticmaterialscombinedwiththequitestartlingpropertieswhichthesematerialsappeartohave;allofwhichprovokesdebateaseachnewfacetoftheirbehaviourisrevealed.Experimenthasbeenvitaltoresolutionofcontroversyandhaschieflybeeninthemicrowaveregi
4、onofthespectrumthoughthereispotentialintheopticalregioncurrentlybeingexploredbyseveralgroups.1.BendinglightthewrongwaymaterialslightwouldbebentthewrongwayrelativetotheSomeyearsagoVeselago[1]madeatheoreticalstudyofnormal.Figure2illustratesrefractionatsuchaninterface.m
5、aterialsinwhichthesignoftheelectricalpermittivity,energyflowandε,andmagneticpermeability,μ,weresimultaneouslygroupvelocitynegative.Heconcludedthat,althoughthesematerialsshouldsupportelectromagneticwaveshavingawelldefinedwavevector,22k=εμω,therewassomethingdecidedlype
6、culiaraboutthesewaves:theorypredictedthattheenergyflowasdictatedbythewavevelocityPoyntingvectorwouldbeintheoppositedirectiontothewavevector,theimplicationbeingthatraystravelintheoppositedirectiontowaves.Seefigure1.Figure1.MaterialswithnegativerefractionaresometimesTh
7、ereversalofenergyflowcaneasilybeunderstood:calledlefthandedmaterialsbecausethePoyntingvectorflippingthesignofbothεandμisequivalentinhastheoppositesigntothewavevector.Maxwell’sequationstoflippingthesignofthemagneticfieldbutkeepingthesamewavevector.SolutionsareIfthegro
8、upvelocity,vg,isnegativeitfollowsthat,exactlythesameassolutionsforaconventionalpositivesystemexceptforthisinversion.SincethePoyntin
