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ID:20767030
大小:1.27 MB
页数:43页
时间:2018-10-15
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1、DopplerPrinciplesColorPrinciplesTheDifferencesInGrayscale,strongechoreflectionscausepixelstobedisplayed.InColorandDoppler,changesinfrequencycausepixelstobecolored.ADopplerProcessorTheDopplerprocessorputsadotonthe“spectrum”basedonthevelocityofamovingobject.Dopple
2、rProcessorWhenthereareobjectsmovingatdifferentspeeds,theDopplerprocessordisplaysadotforeachobject.DopplerProcessorTheverticalpositionrepresentstheobject’svelocity.DopplerProcessorWhenseveralobjectsmoveatthesamevelocity,thecorrespondingdotonthespectrumisbrighter.
3、DopplerProcessorDopplerInformationVelocityTurbulenceIntensityThereare3keypiecesofinformationinaDopplersignalIngeneral,flowtowardthetransducerwillbeabovethebaseline,andflowawayfromthetransducerwillbebelowthebaseline.PopQuiz1.Describe3keydifferencesbetweenthetwoDo
4、pplerWaveformsbelow.2.Matchthewaveformwiththesamplevolumeposition.AB21TheAngleProblemIftheflowisn’tparalleltotheultrasoundbeam,theultrasoundsystemonlysee’saportionofthevelocity.ActualVelocityApparentVelocityTheAngleProblemThetransduceronly“sees”aportionofthetota
5、lvelocity.TheAngleProblemOntheotherside,theapparentdirectionappearstobeopposite,eventhoughtheflowdirectionisthesame!TheAngleProblemAndinthecenter...thereisNOapparentflow.Dopplerprocessorscannotseeflowperpendiculartotheultrasoundbeam.TheDopplerEquationDon’tmemori
6、zethis.Butrememberacoupleofrulesofthumb:WHATSOWHATTheapparentvelocityisYouwon’tgetmuchflowwhendependentontheangle()theangleisnear90°ThehigherthetransmitLowerfrequencyprobesarefrequency(ft),thelowertheusedtomeasurehigherdetectedvelocityvelocitiesv=fd·c2ftcos
7、TheAliasingProblemWhatifyoucheckedyourclockevery5seconds...whatwouldyouseeonthesecondhand?1234TheAliasingProblemWhathappensifyoulookatthesameclockevery55seconds?111098PopQuizHowoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?12PopQu
8、izHowoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?126Every29.99999secondsPopQuizHowfastcantheclockbe,ifyou’regoingtoaccuratelydemonst
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