Fiber Bragg Gratings and Two Wave Mixing Spectral Demodulator System for Impact Detection and Localization

摘要

Multiplexed fiber Bragg grating (FBG) sensors capable of dynamically measuring high frequency (>200KHz) ultrasonic waves using a two wave mixing spectral demodulator has been reported by us previously. The two-wave mixing spectral demodulator enables multiplexing of several FBG sensors and also acts as a high pass filter eliminating low frequency thermal drift and vibrational noise without the need for stabilization as required by other interferometric demodulation schemes. We have demonstrated that this system is capable of monitoring and locating of impact events if several FBG sensors are used. In this paper, we present recent results that have extended our original architecture to take into account the directional dependence of FBG sensor sensitivity to propagating ultrasonic waves. Since the FBG is highly directionally dependent at high frequencies, a simple rosette FBG pattern is implemented enabling effective detection of impact from any location.