Developing self-calibrating system for fiber Bragg grating based guided wave sensing under changing temperature conditions

Abstract

Fiber Bragg grating (FBG) sensors have long been thought of as the ideal sensors for structural health monitoring (SHM) due to their small size, light weight, ability to be embedded and ability to be multiplexed. So, FBG sensors have been commonly used for strain based SHM. In recent times, a renewed interest is seen in the use of FBG sensors for guided wave (GW) measurements using the edge filtering approach which increases the sensitivity several folds. They offer several unique opportunities for GW based SHM such as allowing mode filtering, acoustic coupling, etc. Unfortunately, more wide spread research is limited by the steep learning curve. Also, the use of FBG in real applications is still in its infancy due to the need of calibration of the system when the ambient temperature conditions change. This paper precisely tries to address these two shortcomings. For overcoming the steep learning curve, a detailed discussion on the hardware for the FBG based GW sensing is provided. Following the discussion a step-by-step approach is outlined for incorporating the sensors. A detailed trouble-shooting guide is developed based on the immense experience of the authors in this field. This exercise will allow easier adoption of the technique and stimulate more research in the topic. The exercise also allows us to highlight the safeguards and the features that need to be included in the system which will be self-calibrating. Once the design parameters are established a self-calibrating autonomous FBG based sensing system is developed. The developed system is tested in ambient conditions over an extended period in the day capturing the ambient temperature changes. The system is also tested in a larger temperature range (25 ∘C–65 ∘C). The results indicate that indeed the self-calibrating system works effectively. Some sensitivity studies to determine the performance in terms of system reaction time have also been provided. Such a ‘smart’ autonomous system for GW sensing has not been presented to the best of the author’s knowledge and is the key novelty of the presented work. Furthermore, the detailed discussions and troubleshooting guide will help introduce more people to this field of study which will lead to more radical development of the field.