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超聲波傳感器的工作原理

時(shí)間:2011/11/18閱讀:1244
分享:

     人們能聽到聲音是由于物體振動產(chǎn)生的,它的頻率在20HZ-20KHZ  超聲波傳感器

范圍內(nèi),超過20KHZ稱為超聲波,低于20HZ的稱為次聲波。常用的超聲波頻率為幾十KHZ-幾十MHZ。
   超聲波是一種在彈性介質(zhì)中的機(jī)械振蕩,有兩種形式:橫向振蕩(橫波)及縱和振蕩(縱波)。在工業(yè)中應(yīng)用主要采用縱向振蕩。超聲波可以在氣體、液體及固體中傳播,其傳播速度不同。另外,它也有折射和反射現(xiàn)象,并且在傳播過程中有衰減。在空氣中傳播超聲波,其頻率較低,一般為幾十KHZ,而在固體、液體中則頻率可用得較高。在空氣中衰減較快,而在液體及固體中傳播,衰減較小,傳播較遠(yuǎn)。利用超聲波的特性,可做成各種超聲傳感器,配上不同的電路,制成各種超聲測量儀器及裝置,并在通迅,醫(yī)療家電等各方面得到廣泛應(yīng)用。
   超聲波傳感器主要材料有壓電晶體(電致伸縮)及鎳鐵鋁合金(磁致伸縮)兩類。電致伸縮的材料有鋯鈦酸鉛(PZT)等。壓電晶體組成的超聲波傳感器是一種可逆?zhèn)鞲衅?,它可以將電能轉(zhuǎn)變成機(jī)械振蕩而產(chǎn)生超聲波,同時(shí)它接收到超聲波時(shí),也能轉(zhuǎn)變成電能,所以它可以分成發(fā)送器或接收器。有的超聲波傳感器既作發(fā)送,也能作接收。這里僅介紹小型超聲波傳感器,發(fā)送與接收略有差別,它適用于在空氣中傳播,工作頻率一般為23-25KHZ及40-45KHZ。這類傳感器適用于測距、遙  超聲波傳感器控、防盜等用途。該種有T/R-40-60,T/R-40-12等(其中T表示發(fā)送,R表示接收,40表示頻率為40KHZ,16及12表示其外徑尺寸,以毫米計(jì))。另有一種密封式超聲波傳感器(MA40EI型)。
    它的特點(diǎn)是具有防水作用(但不能放入水中),可以作料位及接近開關(guān)用,它的性能較好。超聲波應(yīng)用有三種基本類型,透射型用于遙控器,防盜報(bào)警器、自動門、接近開關(guān)等;分離式反射型用于測距、液位或料位;反射型用于材料探傷、測厚等。
  由發(fā)送傳感器(或稱波發(fā)送器)、接收傳感器(或稱波接收器)、控制部分與電源部分組成。發(fā)送器傳感器由發(fā)送器與使用直徑為15mm左右的陶瓷振子換能器組成,換能器作用是將陶瓷振子的電振動能量轉(zhuǎn)換成超能量并向空中輻射;而接收傳感器由陶瓷振子換能器與放大電路組成,換能器接收波產(chǎn)生機(jī)械振動,將其變換成電能量,作為傳感器接收器的輸出,從而對發(fā)送的超進(jìn)行檢測.而實(shí)際使用中,用發(fā)送傳感器的陶瓷振子的也可以用做接收器傳感器社的陶瓷振子??刂撇糠种饕獙Πl(fā)送器發(fā)出的脈沖鏈頻率、占空比及稀疏調(diào)制和計(jì)數(shù)及探測距離等進(jìn)行控制。

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