Optical fiber sensing technique for impact detection and location in composites and metal specimens

We present a novel technique for effective detection and location of impacts in metals and graphite/epoxy composite laminates. This scheme employs the highly sensitive extrinsic Fabry-Perot interferometric (EFPI) optical fiber-based sensing system for recording the differential arrival times of impact-generated acoustic signals using a set of four sensors whose location is predetermined. The sensors are surface-mounted on an aluminum sample and completely embedded in the composite specimen. A mathematical model is coded into a computer program to enable real-time, online determination of impact locations. The precise location of the impact can be deduced typically with a 0.5 mm resolution and an accuracy better than 5 mm. An improvement in the sensitivity of this system is proposed by using high-finesse Fabry-Perot cavities which modify the output transfer function curve of the sensor.