水平偏振超聲導波之壓電纖維複材換能器

Abstract

壓電纖維複材導波換能器是由壓電陶瓷纖維、環氧樹脂及印有指叉電極的軟性印刷電路板組成的三明治結構，具有質量輕與可撓性佳等優點，可做為主動結構健康監測的換能器。本研究以垂直壓電陶瓷纖維極化方向的電場驅動壓電纖維複材，產生厚度剪切及面剪切變形，開發配備對稱或反對稱排列指叉電極的壓電纖維複材，作為水平偏振超聲導波換能器，簡稱TH-PFC換能器，以數值模擬與實驗量測比較兩者的致動及感測特性。 本研究量測極化過程中壓電纖維複材的應變，定量分析其極化程度及適當的極化電壓，數值模擬適當的極化電壓引致壓電纖維複材的電場，應用於TH-PFC的極化製程。數值模型的幾何參數是以金相顯微鏡觀測獲得。本研究設計對稱及反對稱指叉電極之TH-PFC，波長分別為12及16個壓電纖維複材單元長度，將其黏貼於厚度1 mm之鋁板，做為導波換能器，數值及實驗結果顯示反對稱指叉電極之TH-PFC的致動及感測能力較強。兩種波長之反對稱指叉電極的TH-PFC皆可有效地激發及感測鋁板的水平偏振TH0、TH1板波，波長為12單元長度之TH-PFC生成的TH1板波響應振幅較強。

Piezoelectric fiber composites (PFC) are made of piezoelectric fibers which are embedded in epoxy resin and sandwiched between flexible polyimide sheets printed with interdigital electrodes. Taking advantages of light weight and conformal ability, PFC has a potential to be a guided wave transducer for active structural health monitoring. This thesis presents a study and development of novel transverse horizontal guided wave ultrasonic transducers made by PFC, which are abbreviated as TH-PFC transducers. The symmetric or anti-symmetric interdigital electrodes can apply electric field perpendicular to the poling direction along fibers and induce face shear or thickness shear deformation. Both actuating and sensing performances of TH-PFC were explored by numerical simulation and experiments. In this work, the axial strain histories of PFC are in-situ monitored during poling process to quantitatively determine the poling situation and adequate voltage application. Geometric dimensions of PFC components were measured using a metallurgical microscope and afterwards applied in numerical simulation. Several prototypes with four combinations, including symmetric or anti-symmetric interdigital electrodes and wave lengths identical to 12 or 16 cell lengths, were developed. The TH-PFC adhered to 1 mm thick aluminum plate can be functioned as plate wave transducers. Numerical and experimental results indicate that TH-PFC equipped with anti-symmetric electrodes has better actuating and sensing capabilities than that with symmetric electrodes. The transverse horizontal plate modes, TH0 and TH1, in aluminum plate can be efficiently excited and detected by the TH-PFC with above wavelengths. The TH-PFC transducers with the shorter wavelength can achieve a larger response in TH1 mode.