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ID:32473162
大小:976.92 KB
页数:48页
时间:2019-02-06
《电磁超声检测机理的实验研究》由会员上传分享,免费在线阅读,更多相关内容在学术论文-天天文库。
1、摘要电磁超声(ElectromagneticAcousticTransducer,EMAT)是无损检测领域出现的新技术,以其精度高、不需要耦合剂、非接触、适合于高温检测、移动检测和相控阵操作,以及容易激发各种超声波型等优点,正越来越受到人们的关注和重视。其缺点为换能效率低,信号微弱,需要在检测中克服。论文首先在论述多年来电磁超声技术发展和应用,总结前人研究成果的基础上,对EMAT的电-声换能机理进行了探讨,分析了洛仑兹力、磁性力和磁致伸缩力产生电磁超声的理论基础,并与压电超声进行了比较,设计电磁超声检测系统的方
2、案,并对其关键的阻抗匹配进行了研究,指出了阻抗匹配的重要性,给出了一种有效的阻抗匹配方法。其次通过设计电磁超声接收实验,对多种条件下实验结果的比较与分析,实验中电磁超声信号出现位置与理论计算值差别较小,表明接收到的信号是电磁超声信号。最后在电磁超声激励实验中,设计电磁超声线圈,通过对电磁超声线圈、偏置磁场、被测体和阻抗匹配网络进行合理的组合,利用回折线圈在铝中激励出表面波、板波、垂直偏振横波,在不锈钢铝板中激励出板波,利用平面螺旋线圈在铝块中激励出体波,从而实现了电磁超声的激励和接收,为下一步实验和仪器开发奠定
3、了基础。如果选择合适的超声波模式,将产生电磁超声诸因素进行合理组合,并进行合理的阻抗匹配,精度达到了检测实际应用要求,电磁超声便能应用于实际检测中。由于电磁超声固有的优点,电磁超声检测具有广泛的应用前景。关键词:电磁超声阻抗匹配超声波无损检测IAbstractElectromagneticAcousticTransducer(EMAT)isagloballeadingtechnologyinthefieldofnon-destructivetesting(NDT).ThefeaturesofEMATs,such
4、ashighaccuracy,contactlessness,need-no-couplant,makethemparticularlysuitableforthenondestructiveinspectionunderhightemperature,movingobjectsandphased-array-controlledoperation.Theyalsocaneasilygenerateultrasonicwavesatdifferentmodes.Allthesemeritsmakethematt
5、ractmoreandmoreattentionfromresearchers.However,EMATsalsohavetheirblemishes,suchaslowtransductionefficiencyresultinginweaksignal,whichshouldbeovercomeduringinspection.Firstly,basedonthereviewofEMATtechnologydevelopmenthistoryanditsapplicationactuality,thisth
6、esisdiscussesthemechanismofelectro-acoustictransductionphenomenonofanEMAT,analysestheoreticalbasisofultrasonicgenerationwithEMATduetoLorentzforce,magnetizationforceandmagnetostrictionforce.EMAThasbeencomparedwithpiezoelectricacoustictransducerinthisthesis.Th
7、isthesisdiscussestheimpedancematchingtechnologywhichhasanimportanteffectforEMATandintroducesamethodofdesigningEMATtestingsystem.Secondly,anEMATreceivingexperimentisdesignedinthedissertationanditisshowedthatexperimentaldataapproximatedtothecalculationareassur
8、edlygeneratedbyEMAT.Lastly,EMATultrasonicgenerationindifferentspecimenshavealsobeenexperimentized,afterEMATcoildesigned,impedancenetworkingmatchedandbiasmagneticfieldchosen.Rayleighwave,Lambwave
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