以磁彈薄膜偵測音洩訊號之研究

The Study of Acoustic Emission Signal Detection Based on Magnetoelastic Thin Film

陳凱迪(Kai-Di Chen)

指導教授 ： 楊智媖 ； 陳政雄

國立中正大學/工學院/機械工程學系/碩士(2012年)

摘要

本文利用非晶相鐵磁合金材料-磁彈薄膜(magneto-elastic thin film)為基礎，用來偵測音洩訊號(Acoustic Emission，簡稱AE)，嘗試突破傳統以壓電(Piezoelectric)效應為偵測機制，將薄膜偵測結果與商用壓電式Kistler AE Sensor互相比較，討論與分析訊號差異性，期許能發展以薄膜為感測媒介，達到低成本、非接觸式及高靈敏度等優點。音洩波偵測是將磁彈薄膜黏貼於不銹鋼板上，以金屬工具敲擊於鋼板上激發出暫態性彈性波，波會以振動形式從鋼板內部傳遞至鋼板表面，當黏貼於鋼板上的磁彈薄膜受到此應變時，將改變薄膜的磁晶排列順序，造成導磁率改變，進而使磁場產生變化，再利用纏繞於薄膜上的感應線圈，以互感原理將磁場物理訊號轉換成電壓訊號，最後透過本研究自行開發之硬體電路做訊號處理，求得音洩訊號與對應電壓之關係。在鋼板不同固定邊界條件下，以金屬工具敲擊鋼板，利用三種感測器偵測鋼板訊號，磁彈薄膜與加速度規偵測出來的頻率約落在15kHz以內，屬於較低頻振動訊號，故磁彈薄膜目前還尚未能偵測出較高頻的音洩訊號；而Kistler AE Sensor在兩種不同邊界條件下，均能偵測出高頻音洩訊號，其頻率大約落於50kHz內。在不同薄膜尺寸實驗中，4cm*4cm尺寸的薄膜，所偵測到的主要振動頻率約為250Hz，隨著薄膜體積的縮小(3cm*3cm、2cm*2cm、1cm*1cm)，其訊號頻率愈高，但振幅值並不受影響。而偏磁鐵在磁場強度為840高斯時，其訊號大約為42mV，當強場強度改為170高斯時，訊號則明顯變小為23mV，故偏磁場強度愈強，薄膜則愈靈敏，而在無外加偏磁下，無法偵測到明顯訊號。最後實驗驗證以水平方向及垂直方向對薄膜偏磁，水平方向的訊號約為37.6 mV，垂直方向則為32mV，故兩種不同偏磁場方向其訊號差異性並不太，因此偏磁方向的改變對薄膜訊號結果影響不大。

關鍵字

非晶相 ； 磁彈薄膜 ； 音洩 ； 壓電 ； 感應線圈

並列摘要

In this study, the acoustic emission (AE) signals were detected based on magneto-elastic thin film of amorphous ferromagnetic alloy materials, which try to surmount conventional detection mechanism that based on piezoelectric effect. To compare the results of thin film and commercial piezoelectric Kistler AE Sensor , discuss and analysis the signals differences both of them. Expect the method can be developed that use sensing medium based on thin film, to achieve the advantages of low-cost、non-contact and high sensitivity, etc. The magneto-elastic thin film was bonded on stainless steel plate to detection AE waves, which the hammer percussion on steel plate. The transient elastic waves were excited, and it transmission to steel plate surface from inside of steel plate by vibrations form. When the strain was applied on magneto-elastic thin film of steel plate, that the magneto-crystalline arrangement sequence of thin film were changed, so that the permeability also were changed, further occur changes of magnetic field of thin film. That transform physical signals of magnetic field to voltage signals by mutual induction principle of sensing coil was wrapped on thin film. Final, through hardware circuit was developed by ourself for signal processing in the research, to obtained the relationship between AE signals and corresponding voltage. The signals frequency were detected about 15kHz of magnetoelastic thin film and accelerometer in the different fixed boundary conditions of steel plate , it’s belong the lower frequency of noise or vibration signals , thus , the higher frequency of acoustic emission signals has not been able to detect by thin film . But , the signals of acoustic emission can be detected by Kistler AE Sensor in the two boundary conditions , the signals about under 50 kHz . In the differernt size of thin film experiment , the signals frequency were detected about 250Hz by 4cm*4cm thin film size 、3cm*3cm frequency of thin film about 300 Hz、2cm*2cm about 350 Hz、1cm*1cm about 400 Hz , therefore , the smaller of thin film , the higher of signal frequency. When the strength was 840 gauss of DC bias magnet , the signal about 42mV , but the strength was changes to 170 gauss , th signal is smaller significantly , it’s approximately 23 mV , so the stronger of strength of DC bias magnet , the film is more sensitive . Finally , both of horiznotal bias magnetic and vertical bias magnetic direction for thin film , the signals few differences for this two , so the result are not different of bias magnetic direction were changes .

並列關鍵字

amorphous ； magneto-elastic thin film ； acoustic emission ； piezoelectric ； detection coils