反對稱指叉電極的壓電纖維複材導波換能器

Abstract

本文發展出一種具反對稱指叉電極的壓電纖維複材(簡稱APFC)，可以激發固定波長的撓性板波。單一方向排列的壓電纖維黏著於兩片軟性指叉電極之間，形成三明治結構。反對稱排列指叉電極的電力線與纖維方向成一夾角，提供斜向極化及撓曲致動所需的電場。APFC的質量輕、柔軟度適中，黏貼於具有曲率的結構表面，可作為嵌入式導波換能器，是超音波檢測及結構健康監測研究的關鍵元件。 本文採用有限元素法進行數值模擬，探討電極間距對於APFC頻率響應的影響。並成功製作APFC，測試自由狀態及黏貼於平板基材的動態特性，APFC的工作頻率與電極間距及基材的材料性質與厚度相關。APFC的撓曲共振不因黏貼於基材而消失，惟聲波的工作頻率會稍微改變，激發的板波聲場有高度指向性，訊號強度隨著波傳距離增加呈線性遞減，不同電極間距之APFC具有相似的衰減性。

This thesis develops a new acoustic wave transducer constructed from the anti-symmetric interdigitated electrode piezoelectric fiber composite (APFC). It can be used as a key component to generate fixed-wavelength flexural plate waves for ultrasonic inspection and structural health monitoring applications. The APFC is formed with unidirectional piezoelectric fibers sandwiched between two thin flexible sheets printed with interdigitated electrodes (IDE). The electric field lines induced by anti-symmetrically aligned electrodes are inclined to the piezoelectric fibers. The IDE provides necessary electric field for polling and excitation of flexural plate waves. Because of light mass and moderate flexibility, APFC is ideally conformable to the curved surface of the host structures. The numerical simulation for understanding the dynamic characteristics of APFC was carried out using finite element analysis. The frequency responses of APFC are explored as a function of the electrode pitch. This study also successfully fabricated prototype APFC, and the performance tests were conducted. The operating frequency of APFC is relevant to the electrode pitch as well as the material properties and thickness of the host structures. The flexural resonances of APFC still remain when it is adhered to an aluminum host plate. The acoustic field induced by APFC has high directivity and small energy dissipation. The amplitude linearly decreases with increasing travel distance. The similar attenuation characteristics can be found in the APFC with different electrode pitches.