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ID:43530924
大小:1.27 MB
页数:43页
时间:2019-10-10
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1、DopplerPrinciplesColorPrinciplesTheDifferencesInGrayscale,strongechoreflectionscausepixelstobedisplayed.InColorandDoppler,changesinfrequencycausepixelstobecolored.ADopplerProcessorTheDopplerprocessorputsadotonthe“spectrum”basedonthevelocityofamovingobject.DopplerProcess
2、orWhenthereareobjectsmovingatdifferentspeeds,theDopplerprocessordisplaysadotforeachobject.DopplerProcessorTheverticalpositionrepresentstheobject’svelocity.DopplerProcessorWhenseveralobjectsmoveatthesamevelocity,thecorrespondingdotonthespectrumisbrighter.DopplerProcessor
3、DopplerInformationVelocityTurbulenceIntensityThereare3keypiecesofinformationinaDopplersignalIngeneral,flowtowardthetransducerwillbeabovethebaseline,andflowawayfromthetransducerwillbebelowthebaseline.PopQuiz1.Describe3keydifferencesbetweenthetwoDopplerWaveformsbelow.2.Ma
4、tchthewaveformwiththesamplevolumeposition.AB21TheAngleProblemIftheflowisn’tparalleltotheultrasoundbeam,theultrasoundsystemonlysee’saportionofthevelocity.ActualVelocityApparentVelocityTheAngleProblemThetransduceronly“sees”aportionofthetotalvelocity.TheAngleProblemOntheot
5、herside,theapparentdirectionappearstobeopposite,eventhoughtheflowdirectionisthesame!TheAngleProblemAndinthecenter...thereisNOapparentflow.Dopplerprocessorscannotseeflowperpendiculartotheultrasoundbeam.TheDopplerEquationDon’tmemorizethis.Butrememberacoupleofrulesofthumb:
6、WHATSOWHATTheapparentvelocityisYouwon’tgetmuchflowwhendependentontheangle()theangleisnear90°ThehigherthetransmitLowerfrequencyprobesarefrequency(ft),thelowertheusedtomeasurehigherdetectedvelocityvelocitiesv=fd·c2ftcosTheAliasingProblemWhatifyoucheckedyourclockevery
7、5seconds...whatwouldyouseeonthesecondhand?1234TheAliasingProblemWhathappensifyoulookatthesameclockevery55seconds?111098PopQuizHowoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?12PopQuizHowoftendoyouhavetolookattheclocktocorrectlydeterminet
8、hedirectionofthesecondhand?126Every29.99999secondsPopQuizHowfastcantheclockbe,ifyou’regoingtoaccuratelydemonst
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