The Sensitivity Enhancement of Distributed Fiber Optical Sensors

Distributed sensing with fibre optic sensors (FOS) has many advantages for strain monitoring, shape sensing and damage detection. However there are various factors that affect the sensitivity of the sensors. In this work different parameters such as types of coating and twist pre-stress are investigated to enhance the measurement sensitivity of distributed FOS used in Rayleigh-Backscattering sensing (ODiSI-B manufactured by Luna Innovations), exposed to environmental and operational conditions of aircraft. To enhance the temperature measurement sensitivity, different UV curable materials including UV683, UV639 (manufactured by Permabond Engineering Adhesives Ltd) were adopted as the FOS coating. Comparing with the commonly used coatings such as acrylates and polyimide, these UV curable coatings show different temperature sensitivity, especially in low temperature range (−50^∘ C to 0^∘ C). However, this temperature sensitivity difference decreased significantly when FOS are mounted onto the surface of composite laminates due to the adhesive. To improve the strain measurement sensitivity, different coatings and the twist pre-stress are induced in FOS. Experiments confirm a small enhancement of strain measurement sensitivity with different coatings. A greater sensitivity enhancement is observed when twist pre-stress is induced before the tension experiment.