建筑土木系探地雷達外文中英對照翻譯

-.z外文文獻3PHYSICALPROPERTIESI3.1WHYAREPHYSICALPROPERTIESIMPORTANT?GPRinvestigatesthesubsurfacebymakinguseofelectromagneticfieldswhichpropagateintothesubsurface.EMfieldswhicharetimevaryingconsistofcoupledelectric(E)andmagnetic(H)fields.Asdiscussedinsection2thefieldsinteractwiththesurroundingmedia.Thisinteractionismacroscopicallydescribedbytheconstitutiveequations2.5to2.7.Themannerinwhichtheelectromagneticfieldsinteractwithnaturalmaterialscontrolshowelectro-magneticfieldsspreadintothemediumandareattenuatedinthemedium.Inaddition,thevariationinphysicalpropertiesgivesrisetotheobservedsubsurfacereflectionsobtainedwithaGPRsystem.InmostgeologicalandNDT(non-destructivetesting)applicationsofGPR,electricalpropertiestendtobethedomi-nantfactorcontrollingGPRresponses.Magneticvariationsareusuallyweak.OccasionallymagneticpropertiescanaffectradarresponsesandGPRusersshouldbecognizantofmagneticeffects.Anelectricfieldinamaterialgivesrisetothemovementofelectriccharge,(i.e.,electriccurrent).Thecurrentflowdependsonthenatureofthematerial.Therearetwotypesofchargeinamaterial,namelyboundandfree,whichgiverisetotwotypesofcurrentflow,namelydisplacementandconduction.Inthefollowing,wewillprovideasimpleoverviewofthetwotypesofcurrentflow.Anin-depthdiscussionofelectricalpropertiescanbefoundinthete*tbyVonHippel,(1954).Magneticpropertiesarecontrolledbytheelectricchargecirculationcharacterattheatomicandmolecularlevel.Macroscopicmagneticpropertiesareaddressedbrieflyinthesenotes.VonHippel(1954)addressessomeofthebasicconcepts.3.2CONDUCTIONCURRENTSMostpeopleareveryfamiliarwithelectricalconductioncurrents.Conductioncurrentsarecreatedwhenunbound(free)chargesmoveinamaterial.Theelectronswhichflowinametalwireareane*ampleofconductioncurrent.Inametal,electronsmovethroughthemetallicmatri*totransferchargefromonepointtoanother.Anothercommonconductionmechanismisthemovementofionsinawatersolution.ThelaterismuchmoreimportantinmostGPRapplications.Conductioncurrentsarisewhenfreechargeacceleratestoaterminalvelocity(basicallyinstantaneously)whenanelectricfield(E)isapplied.Aslongastheelectricfieldisapplied,thechargemoves;whentheelectricfieldisremoved,thechargedeceleratesandstopsmovingFigure3-1illustratestheseconcepts.Figure:3-1Conceptualillustrationofchargemovementforconductioncurrents.a)ChargevelocityversustimeafterEfieldapplied.b)Energyise*tractedfromtheappliedelectricfieldversustime.Figure:3-2Whenanelectricfieldisapplied,unboundelectricalchargesacceleratetoaterminalvelocity.Afterinitialacceleration,velocitybecomesconstantandacontinualtransferofenergytothesurroundingmaterialintheformofheatoccursAllthetimethatchargeismoving,themovingchargeisworkingagainstitssurroundingsdissipatingenergyintheformofheat.Themovingchargebumpsinto'non-moving'objectsandtransfersmechanicalenergywhichappearsintheformofheatinthemedium.Conductioncurrentsrepresentanenergydissipatingmechanismforanelectromag-neticfield.Energyise*tractedfromtheelectromagneticfieldandtransferredirreversiblyintothemediumasheat.MathematicallyonedescribestherelationshipbetweenconductioncurrentandtheappliedelectricfieldasindicatedinEquation3-1.QUOTE〔3-1〕Insimplematerials,therelationshipislinearandtheproportionalityconstantisreferredtoastheelectricalconductiv-ity.ElectricalconductivityhasunitsofSiemenspermeter(S/m).Formanyapplications,however,itismoreusefultoworkwithunitsofmilliSiemenspermeter(mS/m).Conductivityisdependentonthechargedensityandtheinter-nalstatisticalmechanicalinteractionofthechargewithitssurroundings.Thesedetailsarebeyondthescopeofthisdiscussion.Itshouldbenotedthatelectricalconductivityandresistivityaredirectlyrelated.RefertoFigure3-3fortherelation-shipandthee*pressionofOhm'slaw.Electricalresistivityistheinverseofelectricalconductivity.Figure:3-3RelationshipbetweencurrentandappliedfieldaswellastherelationshipwillOhm'slawandresis-tively.ItisimportanttonotethattherearesimplificationsintheabovediscussionfromthegeneralformshowninChapter2.Theconductivityisshownasbeingaconstant.Infactitcanbeafunctionoftherateofchangeoftheelectricfield,theamplitudeofelectricfielditself,aswellastemperature,pressureandmanyotherfactors.Asaresult,oneshouldnotbesurprisedtoseebothnon-linearityandfrequencydependentconductivityinrealmaterials.GenerallythesearesecondordereffectsbuttheymustbeconsideredwhenadvanceduseofGPRiscontemplated.ForthisbasicGPRoverview,theywillbetreatedassecondaryissues.3.3DISPLACEMENT(POLARIZATION)CURRENTSDisplacementcurrentsareassociatedwithboundchargeswhichareconstrainedtolimiteddistanceofmovement.E*amplesofthisaretheelectroncloudaroundanatomicnucleus,theelectricalchargeinasmallmetalobjectimbed-dedinaninsulatingenvironment,andtheredistributionofthemoleculardipolemomentintrinsictosomemolecules.Figure3-4depictstheconcept.Whenanelectricfieldisapplied,boundchargemovestoanotherstaticconfiguration.Thistransitionoccursvirtuallyinstantaneouslyafterwhichthechargesnolongermove.Duringthetransition,energyise*tractedfromtheelectricfieldandtheenergyisstoredinthematerial.Whenthefieldisremoved,thechargemovesbacktotheoriginalequilibriumdistributionandenergyisreleased.Thistypeofbehavioristypicalofwhathappensinacapacitorinanelectriccircuit.Energyisstoredbythebuildupofchargeinthecapacitorandthenenergyise*tractedbythereleaseofthatchargefromthedevice.Figure:3-4Conceptualillustrationofchargemovementassociatedwithdisplacementcurrents.Figure3-5depictsthecharacterizationofchargeseparationinamaterial.Whenanelectricalfieldisapplied,dis-placementofchargeinabulkmaterialgivesrisetoadipolemomentdistributioninthematerial.Thechargesepara-tionisdescribedintermsofadipolemomentdensity,D.Inamoreformalderivation,Discalledtheelectricdisplacementfield(seechapter2).Insimplematerials,theinduceddipolemomentdensityisdirectlyproportionaltotheappliedelectricfieldandtheproportionalityconstantisreferredtoasthedielectricpermittivityofthematerialandhasunitsofFarads/m(F/m).Figure:3-5Dipolemomentdensityinducedbyappliedelectricfieldandrelationtodisplacementcurrent.Thecreationofadipolemomentdistributioninthematerialisassociatedwithchargemovement.Theelectriccurrentassociatedwiththischargemovementisreferredtoasdisplacementcurrent.Thedisplacementcurrentismathemati-callydefinedasthetimerateofchangeofthedipolemomentdensity.Theelectricpermittivityisneverzero.Eveninavacuum,thepermittivity,takesonafinitevalueof8.85*10-12F/m(Faradspermeter).Thee*planationforthisliesinthefieldofquantumelectrodynamicsandisfarbeyondthescopeofthisdiscussion.Itisoftenmoreconvenienttodealwithadimensionlesstermcalledrelativepermittivityordielectricconstant,K.AsdepictedinFigure3-6,therelativepermittivityistheratioofmaterialpermittivitytothepermittivityofavacuum.Figure:3-6Dielectricconstantorrelativepermittivityistheratioofpermittivityofmaterialtothatoffreespace.3.4TOTALCURRENTFLOWInanynaturalmaterial,thecurrentwhichflowsinresponsetotheapplicationofanelectricfieldisami*tureofcon-ductionanddisplacementcurrents.Dependingontherateofchangeoftheelectricfield,oneorotherofthetwotypesofcurrentmaydominatetheresponse.Mathematically,thetotalcurrentconsistsoftwoterms;onewhichdependsontheelectricfielditselfandonewhichdependsontherateofchangeoftheelectricfield.QUOTE(3-2)QUOTE(3-3)Quiteoftenitisusefultodealwithsinusoidallytimevaryinge*citationfields.Inthissituation,onefindsthatthedis-placementcurrentsareproportionaltotheangularfrequency.QUOTE(3-4)whereistheangularfrequency.Thedisplacementcurrentsareoutofphasewiththeconductioncurrentsby90°whichiswhatascribinganimaginaryQUOTEaspecttothedisplacementcomponentimplies.Thosefamiliarwithelectricalengineeringcircuitrytermi-nologywillrealizethatthereisaphaseshiftbetweentheconductioncurrentsandthedisplacementcurrentswhichindicatesthatonetermisanenergydissipationmechanismandtheotheroneisanenergystoragemechanism.Asimplifiedplotofdisplacementcurrentandconductioncurrentsaswellastotalcurrentversusfrequencyispre-sentedinFigure3-7.Usuallythereissomefrequencyabovewhichthedisplacementcurrentse*ceedtheconductioncurrents.Inasimplematerialwheretheconductivityandthedielectricpermittivityareconstant,thereisatransitionfrequency,,wherethedisplacementcurrentsandconductioncurrentsareequal.Abovethisfrequency,displace-mentcurrentsdominate;belowthisfrequency,conductioncurrentsdominate.ThisfactorisimportantwhenwedealwithEMwavepropagation.Thisfrequencydefinestheonsetofthelow-lossregimeimportanttoGPR.Figure:3-7Conduction,displacementandtotalcurrentversusfrequency.Mathematicallythetransitionfrequencyisdefined.QUOTE〔3-5〕Inaddition,anothertermcalledthelosstangentisdefined.Thelosstangentistheratioofconductiontodisplace-mentcurrentsinamaterial.QUOTE〔3-6〕Thetermlosstargettendstobemostcommoninelectricalengineeringconte*ts.Conductivityandpermittivityarenotindependentofthee*citationfrequency.Thereisalwayssomevariation.Thistopicisbeyondthescopeofthischapterofthenotesbutthereisconsiderableliterature(i.e.,Olhoeft,1975)onfre-quencydependentelectric3.5MAGNETICPERMEABILITYMagneticpermeabilityisseldomofmajorimportanceforGPRapplications.Forcompletenessandtoaddressthosee*ceptionalsituationswherepermeabilitymaybecomeimportant,wereviewsomeofthebasicaspectsofmagneticpermeability.Magneticpermeabilityisactuallyrelatedtotheintrinsicelectricalcharacteristicsofthebasicbuildingblocksofphys-icalmaterials.Insimpleterms,chargedparticles,whichformatoms,whichinturnmakemolecules,haveaquantummechanicalpropertyreferredtoasspin.Whencombinedwiththechargeontheparticle,spinresultsintheparticlehavingamagneticdipolemoment.Whenanelectronmovesaroundanatomicnucleus,thechargemotioncanalsocreateamagneticmoment.Thesimpleanalogyistohaveelectricalchargeuniformlydistributedonasphericalballandthenspinball.Theresultingrotatingchargeappearstobeacircularloopofcurrent,whichinturngivesonrisetoamagneticdipole.Magneticpropertiesareessentiallythepropertiesofanelectricalchangemovingaroundaclosedpath.alpropertieswhichcanbereferredto.a〕b〕Figure:3-8a)Asimplepicturesuggestingtheoriginofelectronspinmovement;b)relatingthemagneticmomentinducedinanelectroncloudbyachangeinmagneticfieldFigure:3-9Relatingthemagneticmomenttoasimpleelectronorbit.Thedetailsareobviouslymorecomple*butthisprovidesasimplepictorialmodeltouse.Atomsareformedofelec-tronsandprotonsplusneutrons.Theelectricallychangedcomponentshaveintrinsicandorbitalspinwhentheyformmoleculesofagiventypeofmaterial.Theparticularorientationofthespina*esoftheindividualparticlescanbealignedinrandomorstructuredwaysandmaybealteredbyanambientmagneticfield.Ifthemolecularstructuredoesnotacceptrandomspinorientationbutrequiresastructuredcrystallinearchitecture,thematerialcanhaveaper-manentmagnetization.Ifcomponentpartscanmovetoalignparalleloranti-paralleltoanappliedfield,aninducedmagnetizationresponsewillarise.Magneticpermeabilitymeasuresthedegreetowhichindividualdipolemomentsofthebuildingblockscanbealignedormovedfromtheirnormalorientationbyane*ternallyappliedmagneticfield.Themoreoftheindividualmomentsthatcanbemovedintoalignment,themoremagneticallypolarizablethematerial.Themagneticpropertiesofmateri-alsarequantifiedbymagneticdipolemomentdensity.Whenanelectricalcurrentflowsinaclosedloop,themag-neticmomentsis.QUOTE〔3-7〕whereMisthedipolemoment,IisthecurrentandAistheareaoftheloopenclosedbythecurrentfilament.MhasunitsofAm2Forbulkmaterials,thematerialischaracterizedbydipolemomentdensityQUOTE〔3-8〕whichhasunitsofA/m.Visvolume.Whenamagneticfield,H,inducesamagneticmoment,theamountofmomentise*pressedasQUOTE〔3-9〕wherekisthemagneticsusceptibility(andisadimensionlessquantity).Thereisconsiderablesimilaritybetweeninducedmagneticmomentandinducedelectricdipolemomentdiscussedpreviouslyinthedisplacementcurrentsec-tion.Inthematerial,themagneticflu*ise*pressedasQUOTE〔3-10〕andmagneticpermeabilityise*pressedasQUOTE〔3-11〕whereQUOTE〔3-12〕Thetermrelativemagneticpermeabilityise*pressedasQUOTE〔3-13〕inananalogousfashiontorelativepermittivity.Whenbothmagneticandelectricpropertiesvary,relativepermittiv-ityisusuallye*pressedasKetoavoidconfusion.Thepresenceofamagneticfieldinducestheindividualdipolemomenttochangeorientationandlineupwiththeappliedfield.Insomematerialsthealignmentisinthesamedirectionastheappliedfield,whereasinothermaterialsthealignmentmaybeanti-paralleltotheappliedfield.Thesetwotypesofbehaviorreferredtoasparamagnetismanddiamagnetism.Generallytheseresponsesareveryweakandgiverisetosmallvariationsinmagneticpermeability.Typicalvaluesofmagneticsusceptibilityarelessthan10-5.Insomesituations,however,themagneticmomentscanbealignedinlargesections(calleddomains)ofthecrystalstructureofamaterial.Themomentofdomainscanbechangedbythemoleculesinthecrystalstructurebehavinginasympatheticfashionandmovingfromonedomaintoanother.Suchmaterialsareknownasferromagneticmateri-als.Inferromagneticmaterials,thepolarizationcanbequitelargeandhighvaluesofKmintherangeoftensorevenhun-dredsmaybeobservedinmaterialssuchasiron,cobalt,andnickel.Withferromagneticmaterials,thebehaviorismorecomple*inthatthedipolemomentswhenmoved,oraligned,remainaligned.Thisisknownaspermanentmagnetization.Insuchmaterialsthepermeabilityisveryhighandthedynamicbehaviorofthematerialcomple*.Suchmaterialsseldomformalargevolumefractionofsoilsandrocksbuttheirpresenceinsmallamountscanbethedominantfactordeterminingbulkpermeability.Behaviorcanbeverycomple*.Thebehaviorofdipolemomentdensityiscontrolledbyhowdomainsmove,growandchangeorientationwhichcanbefielddependent,frequencydependentandtemperaturedependent.Thesubjectsarewellbeyondthescopeofthesenotes.Figure:3-10Ferromagneticdomainstructures:a)singlecrystal,b)polycrystallinespecimen.Arrowsrepresentthedirectionofmagnetization.Figure:3-11Magnetizationofaferromaticmaterial:a)unmagnetized,b)magnetizationbydomainwallmotion,c)magnetizationbydomainrotation.Insoilsandrocks,magneticbehaviorisdictatedbytheamountofmagnetite(orsimilarmineralssuchasmeghemiteorilmenite).Thegraph(fromGrant&West(1965))inFigure3-14showshowsusceptibilityvarieswithmagnetitevolumefraction.Thesimpleappro*imateformulaisQUOTE〔3-14〕whereqisthevolumefractionofmagnetiteinthematerial.Toputthisresultinperspective,1%byvolumemagnetite(whichisveryhighinmostcases)contentyieldsKm=1.038.OnlyinrarecaseswillKmbesignificantlydifferentfromunity.Figure:3-12Datafromwhichtheemperialformulaforsusceptibilityk=2.89*10-3V1.01wasderived.[MooneyandBleifuss(7).]-.z中文翻譯3物理性質I3.1為什么物理性質重要探地雷達是利用電磁場的傳播來研究地下空間。電磁場是隨時間變化的一對耦合的電場〔E〕和磁場〔H〕。在第2節(jié)中討論了場與周圍介質的相互作用。本文方程2.5到2.7的宏觀描述了這種相互作用。而電磁場的天然材料，互動的方式，控制電磁場在基質中的擴散、衰減。此外，在地下反射與雷達系統(tǒng)獲得觀測物理性能的產生到變化。在大多數(shù)探地雷達的地質和NDT〔無損檢測〕應用中，電氣性能往往是主要控制探地雷達響應的因素。磁場的變化通常是弱的。磁性能偶爾的影響雷達的反響，探地雷達用戶應該認識到磁效應。電場在材料中產生電荷的運動，〔即，電流〕。當前的流動取決于材料的性質。材料中有兩種類型的電荷，即束縛和自由，其產生兩種類型的束流，即位移和傳導。下面，我們將提供一個簡單的的電流流動的兩種類型的概述。在希佩爾文本〔1954〕可以看到關于電氣特性的深入探討。原子和分子水平上的電荷循環(huán)特性控制著磁性。希佩爾〔1954〕的筆記提出宏觀磁特性簡要討論和根本概念。3.2、傳導電流大多數(shù)人都非常熟悉電流的傳導。材料中未束縛的〔自由〕電荷運動創(chuàng)造出傳導電流。金屬絲的電子流是傳導電流的一個例子。在一種金屬，電子通過金屬基體的電荷從一點傳輸?shù)搅硪粋€。另一個常見的傳導機制是在水溶液中的離子的運動，是探地雷達中更重要應用。自由電荷加速到終端速度〔根本上瞬間〕時應用電場〔E〕產生傳導電流。圖3-1展示了僅利用電場使電荷運動拆下，減速和停頓移動的這些理念。圖3-1：傳導電流電荷運動的概念圖。a〕應用E場后電荷的速度與時間。b〕施加的電場隨時間提取的電能。圖3-2：當施加電場時，自由的電荷在初始加速度后，加速到終端速度。速度常數(shù)和在對周圍材料的能量連續(xù)轉移為以熱的形式出現(xiàn)。運動消耗所有的時間，運動的電荷能量耗散是在其周圍以熱的形式。運動電荷碰到的靜止物質并以熱的形式在介質中傳送機械能。傳導電流電磁場的能量耗散的機制。從電磁場的能量轉移到基質中提取和不可逆熱。數(shù)學描述傳導電流和電場之間的關系表示公式。QUOTE〔3-1〕對簡單的材料，導電性比例常數(shù)為線性關系。電導率的單位為西門子/米〔S/M〕。但是，對于許多應用程序，單位毫西門子每米〔MS/米〕，它是更有用的。導電性電荷密度和部統(tǒng)計力學是依賴于電荷與周圍的環(huán)境的相互作用。這些細節(jié)超出了本文討論的圍。值得注意的是，電導率和電阻率有直接的關系。引用3-3歐姆定律的表達的關系。圖3-3：電流和外加磁場的關系以及將歐姆定律，電阻性能之間的關系。根據上文第二章所討論的關于簡化的重要性需重視。電導率顯示為一常數(shù)。事實上，它可以對電場的變化率，電場振幅本身，以及溫度，壓力和許多其他因素的函數(shù)。其結果，應不要對兩個非線性和頻率所依據的真實材料感到驚奇。。通常這些都是二階效應，但他們必須考慮使用探地雷達先進設想。這個根本的探地雷達概述，他們視其為次要的問題。3.3位移〔極化〕的電流位移電流與電荷的運動有限距離的約束有關。這樣的例子如原子核周圍的電子云，在一個小的金屬物體在絕緣環(huán)境嵌入的一個電荷，且再分配的分子偶極矩的一些分子特性。圖3-4所描繪了這樣的概念：當施加電場時，束縛電荷移動到另一個靜態(tài)狀態(tài)。這種轉變發(fā)生幾乎瞬間之后，不再動彈受指控。在過渡期間，能源從電場和能量提取并存儲在材料中。場被消除時，電荷回到原來的平衡分布且釋放能量。這種發(fā)生在電子電路中的電容器行為是典型的。能量是由電容器中存儲的電荷的積累，然后能源是由從器件釋放的該電荷中提取。圖3-4：位移電流與電荷運動的有關概念圖。圖3-5描述材料中電荷的別離表征。當一個電場，在散裝材料的電荷位移引起材料中的偶極矩分布。電荷別離效果是用一個偶極矩密度來描述，根據一個更正式的推導，D.被稱為電位移場〔見第二章〕。在簡單的材料，誘導偶極矩密度成正比外加電場和比例常數(shù)稱為材料的介電常數(shù)，單位為法拉/米〔F/M〕。圖3-5：偶極矩密度和電場誘導的位移電流的關系。材料中創(chuàng)造的偶極矩的分布與電荷的運動有關。電流與此相關的電荷運動被稱為位移電流。位移電流是數(shù)學上定義的時間變化率的偶極矩密度。介電常數(shù)不會是零。即使在真空，介電常數(shù)，QUOTE為8.85×10-12F/M〔法拉每米〕的有限值。在量子電動力學方面對此的解釋，遠遠超出了本文的討論圍。它往往是更方便的處理的一個無量綱的術語稱為相對介電常數(shù)和介電常數(shù)，K。圖3-6所示，相對介電常數(shù)是材料介電常數(shù)與真空介電常數(shù)的比率圖3-6：介電常數(shù)或相對介電常數(shù)材料的介電常數(shù)，自由空間的比率3.4總電流任何的天然材料，電場的應用電流是一種混合的傳導和位移電流。根據電場的變化率，目前可能會占主導地位的有一個或其他的兩種類型。在數(shù)學上，總電流包括兩個方面；一個取決于電場本身和一個取決于電場的變化對率。QUOTE(3