A Point-Wise Fiber Bragg Grating Sensor to Measure the Vibration of a Cantilever Plate Subjected to Impact Loadings

Abstract

In this paper, an out-of-plane point-wise fiber Bragg grating (FBG) displacement sensing system is proposed and the application of the FBG sensor is extended for modal analysis of a cantilever plate with highly accurate dynamic measurement results. From the proposed FBG sensing system, the relationships between mode shapes and transient displacement responses of the cantilever plate subjected to impact loadings are discussed in detail. By comparing with a laser Doppler vibrometer (LDV) simultaneously, the proposed FBG displacement sensing system demonstrates extremely high sensitivity and resolution. A long-period fiber grating (LPFG) filter-based wavelength-optical intensity modulation technique is employed to demodulate the responses of the FBG. By employing the fast Fourier transform on the measured transient displacement responses, the resonant frequencies of the cantilever plate are determined. An optical full-field measurement technique called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) and FEM numerical calculations are also used to provide full-field vibration mode shapes and resonant frequencies of the cantilever plate. Finally, the amplitude of the frequency spectrums obtained from FBG and LDV are emphasized from the mode shapes and impact locations. The experimental results show that the proposed FBG displacement sensor is able to measure transient out-of-plane point-wise displacement responses and can also be used to determine the resonant frequencies of the cantilever plate.