简介：Thedispersioncharacteristicsandexcitationmechanismsoftheguidedwavesinmultilayeredplatesarestudiedinthispaper.Firstly,thedispersionequationisobtainedbythepropagatormatrixmethod.Then,thebisectiontechniqueisemployedtofindalltherootsofthedispersionequation.Thedispersioncharacteristicsoftheguidedwavesareinvestigatedandanalyzed.ForthemultilayeredplatesinwhichtheS-wavevelocityincreasesordecreasesfromtoptobottom,itisfoundthatthevelocitylimitsinhighfrequencyofthefirstandhighmodesareequaltotheRayleighwaveandS-wavevelocitiesofthelow-velocitylayer,respectively.ItisalsofoundthatthevelocitylimitsinthehighfrequencyofallmodesareequaltotheS-wavevelocityofthelow-velocitylayerfortheplatewithalow-velocitymiddlelayer.Thenormaldisplacementspectrumofallthemodesexcitedbythenormalforcesourcewithadefinitewidthonthesurfaceoftheplateisalsoinvestigated.ItisprovedthatthedominantmodeisthefirstmodewhentheS-wavevelocityincreasesfromtoptobottomlayerandthedominantmodeisdifferentindifferentfrequencyrangefortheplatewithalow-velocitymiddlelayer.

简介：Usingultrasonicguidedwavestoassesslongbonefracturesandfracturehealinghasbecomeapromisingdiagnosticissue.Butthemultimodeoverlapoftheguidedwaveschallengesthequantitativeevaluationandclinicalapplication.Inthepreformedstudy,inordertosimplifythesignalinterpretation,thelow-frequencysinusoidialsignalswereusedtoonlyexciteS0andA0modesinfracturedlongbones.TheamplitudesofS0andA0modeswerenumericallyanalyzedwithvariationincrackwidthandfractureangle.Numericalsimulation,basedonthetwo-dimensionfinite-differencetime-domain(2D-FDTD)revealsthatbothS0andA0amplitudesdecreasewiththefracturewidening.However,theincreaseinfractureanglegraduallyenhancestheA0amplitude,whilewithrespecttotheS0mode,itsamplitudeshowsanon-monotonictrendtothevariationinfractureanglewithaturningpointaround45°.TheamplituderatiobetweenS0andA0canreflectthevariationsincrackwidthandfractureangles.ThesimulationillustratesthatultrasonicguidedS0andA0modesaresensitivetothedegreeofbothverticalandobliquefracturesinthelongcorticalbone.Thesefindingsmaybehelpfulforfracturesdiagnosisandhealingevaluationofthelongbone.