| Summary: | 碩士 === 國立交通大學 === 機械工程系 === 91 === 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.
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