脈搏識別概述

脈搏識別就是心率識別(heartbeatidentification)，正常人的心率和脈搏是一樣的.心率的獨特性：Everybody’sgotauniqueheartbeat.Ifsbasedonthesizeandshapeofyourheartandtheorientationofyourvalves,yourphysiology.Itdoesn’tchangeunlessyouhaveamajorcardiaceventlikeaheartattack不受情緒和狀態(tài)影響：Whenyouarenervousandyourheartcanbeatfaster，butelectricallyyourbeatslookthesame.So,whetheritbeatsfasterorslower,itdoesn’treallymatter.Ifsreallyabouttheshapeofthewaves,andwhatthatsignallookslikewhenitcomesoffyourheart.工業(yè)產(chǎn)品Nymi.(Bionym,aspinoffoftheUniversityofToronto)TheNymiisasmall,wearabledevicethatuseselectrocardiogram(ECG)toauthenticateuseridentity.Ineffect,theNymiturnsaperson'sownheartbeatintoauniquekeythatcanbeusedtounlockanyconceivabledevice.TheNymiisawearabledevicethatmeasuresyourheartbeatandusesitasauniquebiometrictoidentifyyou.Youputitononceaday,touchitwithyouroppositehandforafewseconds,itmeasuresyourheartbeats,itconfirmsthatyou-therightfulownerarewearingit,andthenit'sabletocommunicatethatidentitytowhateversystemorserviceyouuse小米智能手環(huán)心率檢測方法：聲：通常是利用超聲多普勒原理來檢查心臟的搏動光：利用光透射或反射血管內(nèi)流動的血液(脈搏)來檢測脈率，通常情況下是等于心率的。目前絕大部分手環(huán)都是這一原理來檢測心率。電：就是大家通常說的ECG信號，它是有人體心臟搏動而產(chǎn)生的毫伏級電信號，心率帶等至少需要兩個以上電極的設(shè)備都屬于這種檢測原理。壓：通常使用一個壓力傳感器來檢測脈博搏動的微弱壓力信號來檢測脈率，有極少手環(huán)使用，主要在血壓檢測中計算血壓和脈率。

工業(yè)界常用檢測方法：1.PPG光電容積脈搏波描記法原理(PhotoPlethysmoGraphy)一束光打在皮膚上，測量反射7透射的光。因為血液對特定波長的光有吸收作用，每次心臟泵血時都會該波長都會被大量吸收，以此就可以確定心跳。缺點:耗電大，會因環(huán)境光干擾。PPG分兩種模式：反射(reflectance-mode)和透射(transmission-mode)o反射就是PPG中的發(fā)生器(emitter)和接收器(detector)位于同一側(cè)，主要測量反射回來的光。透射就是這兩個器位于兩側(cè)，通常由一個夾子固定，現(xiàn)在絕大多數(shù)血氧含量的sensor都是透射的。2.心電信號測量，ECG(心電圖)測量心肌收縮的電信號。和心電圖類似原理。缺點：電路復雜，占PCB空間大。sensor必須緊貼皮膚，放置位置相對固定。心率帶常用。因為需要接觸皮膚，心率帶都會要求貼身穿戴。并且稍微出汗之后測量才會比較準確。CDARMA — — —SITTINGWISDOMTheworld'sfirstsmartcushionthatcanhelppain.振動式，比較少見，最近才有產(chǎn)品出來。因為每次心跳都會引起身體的震動，通過高精度的傳感器捕捉這種震動，再經(jīng)過信號處理可以得到心跳。比如下面的darma坐墊。CDARMA — — —SITTINGWISDOMTheworld'sfirstsmartcushionthatcanhelppain.主流用于身份識別的是ECG信號ECG用于身份識別：ECGbiometricsidentifiespeoplebytheircardiacrhythm,Notjusttheirheartrate,buttheactualshapeoftheirheartbeat獨特性：EngineershavefoundthattheexactshapeofECGspikesvariesfrompersontoperson.Everyonehashisorherownuniqueshape,whichremainsevenduringheartratechangescausedbyexcitementorexercise.Thatshapealsostaysthesameovertime.精度：ECGmetricsarenotasdevelopedastheyarewithfingerprints,althoughwe’reapproachingfingerprintuniqueness,andwe’llprobablyexceedthosemetricsinthenextfewyears.However,ECGmetricsarealreadyfarabovethingslikevoicerecognition信號通道：AllthestudiesonECGbiometricsarebasedonone-channel,two-channel,three-channel,or12-leadECGsignals.Ofthese,ECGasabiometricbasedonasinglechannelisthemoststudied;simplicityplaysamajorroleinthis,sinceonedoesnothavetoworryabouteffectivechannelcombinationschemes.However,inthiscontext,itisnotclearthatsimplerisnecessarilybetter.Manyofthesingle-channelstudiesusethedatafromoneofthechannelsofastandard12-leadECGrecording.信號特征：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信號的variation:Heartrateincreasesmainlycauseshorteningofdiastoleduration(thebaselinefragmentoftheECG)andtheventriculardepolarizationperiod(correspondingtotheSTsegmentintheECG)andattenuationoftheRwaveamplitude.ThedurationoftheQRScomplexdoesn'tchangesignificantlywithheartrateFigure5.VariationofECGofoneindividualwithdifferentheartrates.Figure5.VariationofECGofoneindividualwithdifferentheartrates.ECGcycleshavenosignificantqualitativeorquantitativevariationsovertime,andtheconfigurationofQRScomplexandtheratioofamplitudesremainstable.Variationswithinanhourarealmostidenticalwithvariationswithinsixmonths.ObservedECGvariationsaremorelikelyc