Fiber Optic Acoustic Emission Monitoring System for Condition Based Maintenance

Los Gatos Research is developing light-weight, low-cost, real-time, compact, multi-channel fiber optic (FO) acoustic emission (AE) system for condition based maintenance applications. Using a novel laser-based optical fiber Bragg grating (FBG) sensor interrogation technique combined with state-of-the-art AE method, the instrument is capable of simultaneously measuring strain, temperature, and AE with high resolution and high sensitivity, and is scalable for integrated, multipoint sensing. The high detection sensitivity and accuracy are achieved by the inherently stable laser frequency tracking scheme which integrates the laser control electronics and photo-detector signals together in a dynamic feedback loop circuit to provide stable laser wavelength locking to the Bragg wavelength of the BG sensors. In Phase I, we have demonstrated the FO sensor’s capability to detect real AE sources from crack growth on an aluminum structure under loading. Pencil lead break (PLB) tests were performed, and the FO sensors demonstrated reasonably good AE signal detection sensitivity and reproducibility close to that of piezoelectric sensors. In Phase II, a field-programmable gate array (FPGA)-based multi-channel FO conditioning module, FBG sensors, and AE software and hardware will be integrated into a compact, stand alone, adaptive, dynamically reconfigurable system with AE detection sensitivity comparable to piezoelectric-based AE instrumentation.