ADAPTIVE FIBER BRAGG GRATING DEMODULATOR FOR STRUCTURAL HEALTH MONITORING APPLICATIONS

摘要

An adaptive fiber Bragg grating demodulator is developed for structural health monitoringrnapplications using two-wave mixing interferometer technology. This demodulator uses thernphotorefractive (PRC) InP:Fe crystal to demodulate the spectral shifts from the fiber Bragg gratingrn(FBG) sensor. Any strains applied on the FBG sensors are encoded as wavelength shifts of the lightrnreflected by the FBG sensor. The wavelength shift is converted into phase shifts and thenrndemodulated by a TWM interferometer with unbalanced path in its reference and signal beam. Thernlow frequency signals, such as signals caused by large quasi-static strain or large temperature driftrnapplied on the FBG sensors, are automatically filtered by the demodulator. One of the structuralrnhealth monitoring (SHM) applications, acoustic emission event detection and source locationrndetermination in a plate structure, will be demonstrated using this demodulator. In this application, arnFBG sensor with large dynamic response range is glued on the surface of an aluminum plate. Therndemodulator actively monitors the FBG sensor. Once there is a dynamic spectral shift signal fromrnthe FBG sensor, the demodulator will be triggered to record the signal from the FBG sensor. Thernrecorded signal is used to determine the source location of the acoustic emission event by waveletrntransform technique.