Investigation of the transient behavior of a cantilever using a point-wise fiber Bragg grating displacement sensor system

This paper presents a fiber Bragg grating (FBG) sensor system setup method to measure the transient response of dynamic displacement for a cantilever subjected to impact loadings. An LPFG filter-based wavelength?optical intensity modulation technique is used in this study. The transient responses of particle motions measured by an FBG displacement sensor are compared with those obtained simultaneously by a laser Doppler vibrometer (LDV). The resonant frequencies of the cantilever are determined by employing a fast Fourier transform on the transient displacement responses obtained from the FBG and the LDV. An optical full-field measurement technique called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) is also used to provide the full-field vibration mode shapes and resonant frequencies of the cantilever. The resonant frequencies obtained from four experimental measurement techniques, i.e., FBG, LDV, AF-ESPI, and shaker, are compared with those predicted from theoretical and FEM numerical calculations. Furthermore, the amplitude of the frequency spectra obtained from the FBG and the LDV are emphasized from the mode shapes and impact locations of the steel ball. The proposed FBG displacement sensor is proved to be able to measure transient point-wise displacement responses which can also be used to determine the resonant frequencies of structures.