Damage detection of composite structures using a stabilized extrinsic Fabry-Perot interferometric sensor system

In the case of an extrinsic Fabry-Perot interferometric sensor, a phase compensating technique is particularly necessary in applying the sensor to detecting an acoustic emission signal because of a fade-out problem. The technique makes it possible to maintain the phase at the quadrature point. In this paper, we developed the phase-stabilization control sensor system, which is composed of a broadband light source, a fiber Fabry-Perot (FP) tunable filter and a control-circuit board. We verified the performance of the developed stabilization sensor system through two preliminary tests. One was a test on the stabilization of the phase and the other was a pencil-break test. Finally, the acoustic emissions of fracture signals generated by a tensile test of a cross-ply composite specimen were successfully detected with the help of the phase-stabilization control system, which solved the fade-out problem.