脉搏识别概述

脉搏识别就是心率识别(heartbeatidentification)，正常人的心率和脉搏是一样的.心率的独特性：Everybody’sgotauniqueheartbeat.Ifsbasedonthesizeandshapeofyourheartandtheorientationofyourvalves,yourphysiology.Itdoesn’tchangeunlessyouhaveamajorcardiaceventlikeaheartattack不受情绪和状态影响：Whenyouarenervousandyourheartcanbeatfaster，butelectricallyyourbeatslookthesame.So,whetheritbeatsfasterorslower,itdoesn’treallymatter.Ifsreallyabouttheshapeofthewaves,andwhatthatsignallookslikewhenitcomesoffyourheart.工业产品Nymi.(Bionym,aspinoffoftheUniversityofToronto)TheNymiisasmall,wearabledevicethatuseselectrocardiogram(ECG)toauthenticateuseridentity.Ineffect,theNymiturnsaperson'sownheartbeatintoauniquekeythatcanbeusedtounlockanyconceivabledevice.TheNymiisawearabledevicethatmeasuresyourheartbeatandusesitasauniquebiometrictoidentifyyou.Youputitononceaday,touchitwithyouroppositehandforafewseconds,itmeasuresyourheartbeats,itconfirmsthatyou-therightfulownerarewearingit,andthenit'sabletocommunicatethatidentitytowhateversystemorserviceyouuse小米智能手环心率检测方法：声：通常是利用超声多普勒原理来检查心脏的搏动光：利用光透射或反射血管内流动的血液(脉搏)来检测脉率，通常情况下是等于心率的。目前绝大部分手环都是这一原理来检测心率。电：就是大家通常说的ECG信号，它是有人体心脏搏动而产生的毫伏级电信号，心率带等至少需要两个以上电极的设备都属于这种检测原理。压：通常使用一个压力传感器来检测脉博搏动的微弱压力信号来检测脉率，有极少手环使用，主要在血压检测中计算血压和脉率。

工业界常用检测方法：1.PPG光电容积脉搏波描记法原理(PhotoPlethysmoGraphy)一束光打在皮肤上，测量反射7透射的光。因为血液对特定波长的光有吸收作用，每次心脏泵血时都会该波长都会被大量吸收，以此就可以确定心跳。缺点:耗电大，会因环境光干扰。PPG分两种模式：反射(reflectance-mode)和透射(transmission-mode)o反射就是PPG中的发生器(emitter)和接收器(detector)位于同一侧，主要测量反射回来的光。透射就是这两个器位于两侧，通常由一个夹子固定，现在绝大多数血氧含量的sensor都是透射的。2.心电信号测量，ECG(心电图)测量心肌收缩的电信号。和心电图类似原理。缺点：电路复杂，占PCB空间大。sensor必须紧贴皮肤，放置位置相对固定。心率带常用。因为需要接触皮肤，心率带都会要求贴身穿戴。并且稍微出汗之后测量才会比较准确。CDARMA — — —SITTINGWISDOMTheworld'sfirstsmartcushionthatcanhelppain.振动式，比较少见，最近才有产品出来。因为每次心跳都会引起身体的震动，通过高精度的传感器捕捉这种震动，再经过信号处理可以得到心跳。比如下面的darma坐垫。CDARMA — — —SITTINGWISDOMTheworld'sfirstsmartcushionthatcanhelppain.主流用于身份识别的是ECG信号ECG用于身份识别：ECGbiometricsidentifiespeoplebytheircardiacrhythm,Notjusttheirheartrate,buttheactualshapeoftheirheartbeat独特性：EngineershavefoundthattheexactshapeofECGspikesvariesfrompersontoperson.Everyonehashisorherownuniqueshape,whichremainsevenduringheartratechangescausedbyexcitementorexercise.Thatshapealsostaysthesameovertime.精度：ECGmetricsarenotasdevelopedastheyarewithfingerprints,althoughwe’reapproachingfingerprintuniqueness,andwe’llprobablyexceedthosemetricsinthenextfewyears.However,ECGmetricsarealreadyfarabovethingslikevoicerecognition信号通道：AllthestudiesonECGbiometricsarebasedonone-channel,two-channel,three-channel,or12-leadECGsignals.Ofthese,ECGasabiometricbasedonasinglechannelisthemoststudied;simplicityplaysamajorroleinthis,sinceonedoesnothavetoworryabouteffectivechannelcombinationschemes.However,inthiscontext,itisnotclearthatsimplerisnecessarilybetter.Manyofthesingle-channelstudiesusethedatafromoneofthechannelsofastandard12-leadECGrecording.信号特征：TheECGconsistsofthreemaincomponents:Pwave,QRScomplex,andTwave.Figure1:AtypicalECGsignalthatincludesthreesuccessiveheartbeatsandtheinformationlyingintheP,Q,R,S,andTwaves.Figure2:Extractionofheartbeatintervalfeaturesandinterbeatintervalfeaturesfromsuccessiveheartbeats.Figure3:ExtractionofECGmorphologicalfeaturesfromheartbeatwherefiducialpoint(FP)representsthepositionofRpoint(FP)representsthepositionofRdi(a)normalsignaland(b)scaledsignal.peakFigure4:SchematicrepresentationofECGbiometricsystem.ThesystemperformsautomatedcharacterizationoftheECGsignalandextractionofeigenbeatfeaturesforindividualidentification.ECG信号的variation:Heartrateincreasesmainlycauseshorteningofdiastoleduration(thebaselinefragmentoftheECG)andtheventriculardepolarizationperiod(correspondingtotheSTsegmentintheECG)andattenuationoftheRwaveamplitude.ThedurationoftheQRScomplexdoesn'tchangesignificantlywithheartrateFigure5.VariationofECGofoneindividualwithdifferentheartrates.Figure5.VariationofECGofoneindividualwithdifferentheartrates.ECGcycleshavenosignificantqualitativeorquantitativevariationsovertime,andtheconfigurationofQRScomplexandtheratioofamplitudesremainstable.Variationswithinanhourarealmostidenticalwithvariationswithinsixmonths.ObservedECGvariationsaremorelikelyc