具指叉電極壓電纖維複材導波換能器

Abstract

壓電纖維複材是由壓電陶瓷纖維、環氧樹酯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、撓性佳、貼合彎曲結構等優點。習用之壓電纖維複材(簡稱PFC)具備對稱排列的指叉電極，應用於抑制低頻振動及能量收集。本文探討具反對稱排列指叉電極的壓電纖維複材(簡稱AE-PFC)及PFC的致動與感測高頻板波的能力，以數值模擬與實驗量測比較兩者的動態特性。 本研究量測壓電纖維複材在極化過程中的軸向應變，瞭解極化程度並獲得適當的極化電場值。施加直流高電壓於指叉電極會提供壓電纖維不均勻的極化電場，數值模擬顯示壓電纖維複材在指叉電極之間，方才具有平行纖維方向的極化電場。不均勻的極化電場會減損壓電纖維複材的有效壓電常數，阻抗測試與模擬分析顯示減少的百分比等於指叉電極寬度與電極節距的比率。數值分析顯示AE-PFC具有較佳的致動能力，實驗發現協助AE-PFC進行對稱極化的輔助電極會降低其致動能力。將AE-PFC與PFC黏貼於1 mm厚鋁板做為導波換能器，實驗顯示兩者都可以接收鋁板上A0、S0及A1板波，以5 V低電壓正弦訊號僅能激發出A0與S0板波，輻射聲場的指向性取決於電極重疊長度，重疊長度愈小發散角愈大。壓電纖維複材在共振頻率下激發與接收的訊號強度最大，具備偵測平板圓孔缺陷的能力。

Piezoelectric fiber composite (PFC) is made of unidirectional piezoelectric ceramic fibers embedded in epoxy resin and sandwiched between two flexible printed circuit films with interdigital electrodes. It has comparative advantages of light-weight, flexibility, conformability to curved structures, etc. The conventional PFC featuring symmetrically aligned interdigital electrodes have been used for low frequency vibration suppression and energy harvesting. This study explores sensing and actuating abilities of the piezoelectric fiber composites with antisymmetric interdigital electrodes (abbreviated as AE-PFC) and PFC. Coordinated experiments and numerical simulation were conducted for comparing dynamic characteristics of both devices. In this work, axial strains of PFC during poling process were measured to figure out appropriate poling field. The poling field produced through the interdigital electrodes is not uniform over the whole fibers. Homogeneous poling field only occurs in the region between electrode fingers in accordance with numerical simulation. Impedance test and simulated results indicate inhomogeneous polarization decreases the effective piezoelectric constants by a fraction of the electrode width to the pitch between adjacent electrodes. In simulation, the AE-PFC transducers were found to have better actuation ability than PFC. But according to experimental evidence, the auxiliary electrodes which were used to assist to increase poling field in AE-PFC will decrease its actuation ability. AE-PFC and PFC were adhered on the surface of a 1 mm thick aluminum plate to function as Lamb wave transducers. Both can receive A0, S0, and A1 plate waves, but only A0 and S0 modes can be launched if the transducers are excited by 5 volt sinusoidal tone bursts. Directivity of the radiation patterns from both transducers depends on the overlapping length of the electrodes. The longer overlapping length induces the higher directivity. The piezoelectric fiber composites launch and receive stronger plate wave signals at their resonant frequencies. It has been verified both AE-PFC and PFC possess defect detection ability for the circular hole in a plate.