具反對稱指叉電極之壓電纖維複材的模型分析與實驗評估

Abstract

本文以數值模型及實驗探討研發之反對稱排列指叉電極驅動壓電纖維複材(AE-PFC)的特性。AE-PFC是以兩片具有指叉電極的軟性電路板，上下夾持著環氧樹脂黏合的單向排列壓電纖維，形成三明治複材結構。金屬條狀之指叉電極與壓電纖維的軸向垂直，提供極化與致動電場。黏貼AE-PFC於平板結構，施以週期電壓，可激發固定波長的撓性板波。本研究證實AE-PFC是具備低電壓驅動能力的導波換能器，具有結構健康監測的應用潛力。 數值分析結果有助於改善低電壓驅動AE-PFC的能力，提高指插電極寬度與間距比例可增加極化電場強度，對稱排列的指叉電極能夠提供兩倍於反對稱者引致的極化電場強度，增加壓電纖維高分子母材之介電係數可以改善極化電場的均勻性。實驗量測AE-PFC激發之近場範圍近似於活塞探頭激發的菲涅耳區公式，但是卻大於換能器附加質量對於結構平板影響區的數值結果。

This thesis studies the characteristics of a novel guided wave transducer using numerical investigation and experimental measurement. The acoustic transducer called antisymmetric interdigitated electrode piezoelectric fiber composite (AE-PFC) is formed with a number of unidirectional piezoelectric fibers embedded in epoxy resin and sandwiched between two thin flexible sheets printed with interdigitated electrodes (IDE). The metal stripes of IDE perpendicular to the fibers provide the poling and actuating electric field. Constant wavelength flexural waves can be transmitted if the AE-PFC is adhered to a host plate and exerted by periodic voltages. This study indicates that the AE-PFC can be used as a low-voltage drive guided wave transducer with very good potential in application of structural health monitoring. Numerical exploration benefits the improvement of low-voltage drive capability of AE-PFC. The induced poling electric field intensity increases as decreasing the space between two adjacent electrodes to the electrode width ratio. The intensity of electric field generated by the IDE aligned symmetrically is twice as many as that placed anti-symmetrically. Increasing the dielectric constant of polymer matrix surrounding piezoelectric fibers will improve the homogeneity of electric field. Experimental evidence indicates that the measured acoustic near field transmitted from AE-PFC is approximate to the Fresnel zone formula of a piston transducer. It remains greater than of the influenced zone determined by added mass effect resulted from the transducer on the host plate.