Optical fiber-based corrosion sensor systems for health monitoring of aging aircraft

Increased service requirements for current military aircraft fleet are extending lifetimes and environmental exposure past original design criteria. It is therefore critical that corrosion be detected before structural integrity is compromised and repair becomes economically prohibitive. Robust, cost effective methods of corrosion detection and monitoring are needed. One approach to corrosion monitoring is to measure the environmental species that typically preclude the initiation of corrosion or reveal its propagation. Novel optical fiber-based sensors for real-time in situ detection of corrosion precursors and by-products have been developed for health monitoring and maintenance of aging aircraft. The developed system consists of optical fiber long-period grating (LPG) sensors multiplexed using an optical switch and a low-cost miniature spectrum analyzer. The LPG sensors operate based on specially designed hydrogel coatings which cause a measurable change in the refractive index measured by the LPG in the presence of specific target species. Application of optical fiber-based chemical sensors for the detection of water ingress in lap joints, and metal-ion detection are presented and discussed.