雙頻道表面聲波感測系統研製與應用

Abstract

本實驗利用碳六十/ 聚苯乙炔C60-polyphenylacetylene (C60 – PPA)與Polyvinylpyrrolidone（PVP）作為表面聲波感測器(surface acoustic wave ,SAW)之塗佈物質分別對二硫化碳（carbon disulfide,CS2）及甲醇（methanol,CH3OH）進行感測，藉由表面聲波晶片上塗佈物質吸附二硫化碳或甲醇導致表面聲波感測器頻率下降來進行偵測。在此實驗系統中，利用自製介面及自撰程式，可同時偵測兩個感測器（雙頻道）並讀取數據及繪圖。 在靜相系統研究中首先選擇六種化合物（C60 – PPA、Nafion、PPA、Crytand [2,2]、Polyethene glycol及Polyvinylpyrrolidone）做為表面聲波晶體之塗佈物，用來吸附及偵測CS2及CH3OH，所選擇的六種塗佈物對於偵測CS2及CH3OH的吸附，均為物理性吸附具可逆性，即均可利用氮氣將CS2及CH3OH脫附。結果並發現C60 – PPA作為塗佈物之表面聲波感測器對於CS2的偵測有較好的靈敏度；相同地，以Polyvinylpyrrolidone作為塗佈物之表面聲波感測器對於CH3OH的偵測比其他的塗佈物有較好的靈敏度。此外，並研究塗佈物（C60 – PPA及Polyvinylpyrrolidone）量的多寡對於偵測氣體的影響，結果發現，C60 – PPA塗佈量約為500 ng對於偵測CS2有最佳的靈敏度，而Polyvinylpyrrolidone塗佈量對於偵測CH3OH的訊號值約呈線性關係，我們選擇與C60 – PPA相同的塗佈量（約500 ng）。 在動相氣體表面聲波感測系統研究上，利用自製的感測工作槽對CS2及CH3OH感測，研究討論其濃度效應、流速效應和再現性。此動相氣體SAW顯示對於CS2及CH3OH感測有很好的靈敏度及再現性。 在雙頻道SAW系統，以C60 – PPA塗佈的表面聲波感測器偵測CS2，結果發現，其偵測下限為0.4 ppm，再現性（RSD= 3.37﹪，n = 10）；相同地，以PVP塗佈的表面聲波感測器偵測CH3OH，其偵測下限為0.05 ppm，再現性（RSD= 0.86﹪，n = 10）。研究中也對於有機物質（丙酮、丙醇、丙胺）是否會干擾CS2及CH3OH偵測進行研究，除了丙胺對於C60 – PPA會造成不可逆吸附會影響CS2的偵測，其餘大部分干擾物對SAW系統影響不大。 前述實驗中二硫化碳（CS2）、甲醇（CH3OH）個別偵測或混合偵測後，各30組數據經倒傳遞類神經網路（back-propogation artificial neural network,BPN）分析，不管是網路學習或網路測試皆可100﹪將CS2、CH3OH分辨出來，誤判率為0，此結果顯示BPN可成功將其定性化。此外應用多元迴歸分析（multiple regression analysis,MRA）也可成功將CS2及CH3OH定量化。

C60-polyphenylacetylene(C60-PPA) and polyvinylpyrrolidone(PVP) coated two-channel surface acoustic wave (SAW) detection system was developed and employed to detect carbon disulfide (CS2) and methanol (CH3OH) in this study. The frequency of surface acoustic wave oscillator decreases due to the adsorption of gas molecules on the coated materials of the SAW sensor. The two-channel SAW detection system also includes a homemade computer interface for data acquisition and data processing with a computer program in BASIC. In the stationary system, six coating materials (C60-PPA, nafion, PPA, crytand [2,2], polyethene glycol and PVP ) were used to absorb and detect carbon disulfide and methanol gases. The adsorption of all the six coating materials to CS2 and CH3OH was found to be physical adsorption (a reversible type), which could be desorbed by introducing N2 gas.The C60-PPA coated SAW detector exhibited more sensitive to CS2 than the other coating materials. In contrast, the PVP coated SAW detector exhibited more sensitive to CH3OH than the other coating materials. Then , coating load effect on the response of the SAW crystal was investigated and discussed.When 500 ng C60-PPA coated SAW detection system for CS2 showed the best sensitivity. Coating load effect of polyvinylpyrrolidone coated SAW sensor for CH3OH showed the linear relationship so we chosen to coat polyvinylpyrrolidone as much as C60-PPA. In SAW mobile gas system, the SAW sensor with the homemade working cell was prepared to detect CS2 and CH3OH. Effects of concentration, flow rate and reproducibility on frequency response of surface acoustic wave sensor were studied and discussed. The SAW gas sensor obviously showed the good sensitivity and reproducibility for CS2 and CH3OH. In bi-channel SAW detection system, the C60-PPA coated SAW showed the good detection limit of 0.4 ppm and good reproducibility with RSD of 3.37﹪( n＝10) for CS2. Similarly, the PVP coated SAW also showed the good detection limit of 0.05 ppm and good reproducibility with RSD of 0.86﹪(n＝10) for CH3OH in bi-channel SAW detection system. The interference effect of organic molecules (aceton, 1-propanol and n-propylamine) on the SAW detection system wasnegligible except that the absorption of C60-PPA to propylamine was found to be irreversible type. The frequency signals from the two channel SAW sensor array were processed by back-propagation artificial neural network（BPN）and multiple regression analysis（MRA）.The qualitative and quantitative analyses of CS2 and CH3OH in their mixtures has been successfully realized by using the sensor array,BPN and MRA.