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超聲波傳感器的工作原理

時(shí)間:2011/11/18閱讀:1239
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     人們能聽(tīng)到聲音是由于物體振動(dòng)產(chǎn)生的,,它的頻率在20HZ-20KHZ  超聲波傳感器

范圍內(nèi),,超過(guò)20KHZ稱(chēng)為超聲波,低于20HZ的稱(chēng)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(guò)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(cè)量?jī)x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(lèi),。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(lèi)傳感器適用于測(cè)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(kāi)關(guān)用,它的性能較好,。超聲波應(yīng)用有三種基本類(lèi)型,,透射型用于遙控器,防盜報(bào)警器,、自動(dòng)門(mén),、接近開(kāi)關(guān)等;分離式反射型用于測(cè)距,、液位或料位,;反射型用于材料探傷、測(cè)厚等,。
  由發(fā)送傳感器(或稱(chēng)波發(fā)送器),、接收傳感器(或稱(chēng)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(dòng)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(dòng),,將其變換成電能量,,作為傳感器接收器的輸出,從而對(duì)發(fā)送的超進(jìn)行檢測(cè).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,。控制部分主要對(duì)發(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(cè)距離等進(jìn)行控制,。

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