不同電極型式擬側場激發聲波感測器之研究

Pseudo-LFE Acoustic Wave Sensors with Different Electrode Configurations

徐兆宏(Chao-Hung Hsu)

指導教授 ： 陳永裕

大同大學/工程學院/機械工程學系所/碩士(2012年)

摘要

擬側場激發（pseudo lateral field excited, Pseudo-LFE）聲波感測器具有較小的電性阻抗，已被驗證可在空氣中穩定振盪，並有效地感測液體的電性變化，但相較於側場激發（lateral field excited, LFE）聲波感測器，仍有靈敏度不足的問題，因此本研究利用改變感測電極的幾何來提升Pseudo-LFE感測器之效能。首先，使用有限元素軟體COMSOL來分析各式Pseudo-LFE感測器之振盪模態，包括實心圓與環形的感測電極，並計算其對液體黏滯性、介電常數與導電度之靈敏度。同時，也在AT切面的石英晶片鍍上相對應型式之感測電極，以製作各式Pseudo-LFE感測器，並利用網路分析儀與振盪電路進行測試，所量測的液體包括各種濃度之甘油、異丙醇與鹽水溶液。模擬結果與實驗相當吻合，顯示所發展的數值模型適用於分析Pseudo-LFE感測器。結果也顯示：鍍有環形感測電極之Pseudo-LFE感測器具有接近於LFE感測器之靈敏度，但因為電性阻抗較小，在甘油與異丙醇溶液之濃度較高或液體量減少時，仍能有效地感測。綜觀之，環形感測電極之Pseudo-LFE感測器可大幅提升感測靈敏度，也具有較大的感測範圍，因此可取代傳統之石英晶體微天平（quartz crystal microbalance, QCM）與側場激發聲波感測器，應用於各種液體與氣體之量測。

關鍵字

有限元素法 ； 擬側場激發聲波感測器 ； 頻率飄移

並列摘要

Pseudo lateral field excited (Pseudo-LFE) acoustic wave sensors exhibit stable oscillation in the air due to low electric impedance. Although they are capable of detecting liquid electrical property changes, the sensitivity is not as large as lateral field excited (LFE) acoustic wave sensors. Therefore, this study modifies the sensing electrode geometry to increase sensitivity of a Pseudo-LFE sensor. At first the finite element software, COMSOL, was used to analyze the resonance modes and sensitivities of Pseudo-LFE sensors with various sensing electrode geometries to liquid viscosity, permittivity, and conductivity. Moreover, Pseudo-LFE sensors with ring-shape sensing electrodes were fabricated on AT-cut quartz and measured with an oscillator circuit or network analyzer when contacting with glycerol, 2-propanol, or NaCl solution. The simulation results exhibit similar trend and comparable values with the experiments, verifying the validity of the simulation model proposed here. Besides, Pseudo-LFE sensors with ring-shape sensing electrodes show a comparable sensitivity with LFE sensors and can measure glycerol and 2-propanol solutions of high concentration or less volume. In conclusion, Pseudo-LFE sensors with ring-shape sensing electrodes are potential in sensor applications instead of QCM (quartz crystal microbalance) and LFE sensors because of large sensitivity and wide sensing range.

並列關鍵字

Frequency shift ； Pseudo-LFE piezoelectric acoustic wave sensor ； Finite element method

參考文獻

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