光纖光柵在板波波傳量測上的應用

Abstract

光纖光柵不僅具有偵測溫度及靜態應變的能力，亦具備偵測振動及波動的動態應變之能力。本研究結合光纖光柵感測原理與技術、板波波傳原理及二維快速傅立葉轉換，分析光纖光柵量測板波波傳的頻散特性，驗證光纖光柵具有寬頻偵測頻散板波波傳的能力。光纖光柵除了黏置於鋁板表面，並內埋於複材層板，作為板波感測器。實驗分析得知光柵偵測板波的頻寬與板波波長在光柵上的投影量、光柵的軸向與橫向應變、光纖干涉儀之光臂差及光柵長度有關。

Fiber Bragg gratings have ability not only to detect temperature and static strains of structures but also to measure dynamic responses such as vibrations and ultrasound. This thesis coordinates fiber grating sensing principle, laser-induced ultrasound technique, and two-dimensional fast Fourier transform method to establish a fiber grating system for measuring dispersive plate waves. The fiber gratings are attached on an aluminum plate and embedded in a fiber-reinforced carbon/epoxy composite cross-ply to detect plate waves launched from different orientations. Phase velocity of the plate waves measured by the fiber gratings are in a good agreement with the prediction using first order shear deformation plate theory in a broad frequency range. Experimental and analytic results evidence that the bandwidth of fiber grating system depends on the wavelength projection of plate waves on the grating, axial and transverse strains on the grating, optical path difference of the Mach-Zehnder interferometer, and grating length.