Study on a new kind of surface sticking strain sensor with sensitivity enhanced based on FBG

Fiber Bragg Grating sensors are widely used in the field of optical sensing system for the Structure Health Monitoring (SHM) during the last 10 years. It can be used for monitoring the strain, temperature pressure and some other characters of the structure. In this paper a new kind of surface sticking strain sensor with sensitivity enhanced has been studied and developed. The structure of the sensors is presented and the Ansys software has been used to optimize the structure. A novel theory about how to enhance the sensitivity or widen the scale of the strain sensors based on FBG is introduced too. Based on the theory two types of sensor have been developed. One is the long-scale sensor that is able to monitor the big strain such as crack, the other is the high-precision sensor that is able to monitor the micro strain 0.5με, and we conclude the sensitivity enhancing coefficient. As the sensitivity coefficient of bare fiber is 1.2pm/με, the theoretical enhancing sensitivity coefficient of long-scale sensor is K=3.3811 and the theoretical enhancing sensitivity coefficient of high-precision sensor is K=0.58. Then groups of experiments were carried out to validate the theory. The experimental sensitivity coefficient of long-scale sensor is 0.35pm/με with the coefficient of enhancing sensitivity is K=3.4286. The experimental sensitivity coefficient of high-precision sensor is 1.96pm/με with the coefficient of enhancing sensitivity is K=0.61. Comparing the experimental results with the theory results, it proves that the two types of strain sensors can really reflect the strain status and the damage information of the structure, and it is stable and reliable for the practical project.