The simultaneous measurement of temperature and mean strain based on the distorted spectra of half-encapsulated fiber Bragg gratings using improved particle swarm optimization

A half-encapsulated FBG is capable of simultaneously measuring temperature and strain. However, spectrum distortion, which may be induced by overlapping or non-uniform strains, may hinder the adoption of this technique. In order to resolve this issue, an improved particle swarm optimization (IPSO) based spectra reconstructing method has been adopted in this study to estimate the temperature and mean strain according to the distorted spectrum. Also, a dynamic adaptive inertia weight adjusting strategy based on the swarm success rate has been adopted to improve the algorithm. To validate the method, a total of 48 scenarios of distorted spectra have been simulated, and the temperature and mean strain estimated by IPSO have been compared with the genetic algorithm and linearly-declined PSO. The simulation results indicated that the IPSO based reconstructing method provided a higher accuracy. Additionally, the feasibility of the proposed method has been experimentally verified using a strain tunable apparatus within a measurable temperature environment. The experimental results demonstrated that the half-encapsulated FBG with an IPSO based spectra reconstructing method was applicable for the simultaneous measurement of temperature and mean strain, even when the spectrum was distorted.