Strain transfer in distributed fiber optic sensor with optical frequency domain reflectometry technology

Abstract

Present research on strain transfer in optical fiber sensors focuses on high-precision, point-bonded fiber Bragg grating sensors. The spatial resolution of a traditional distributed fiber optic sensor (DOFS) reaches submeter or meter, and strain transfer in these sensors is rarely noticed. The accuracy of the DOFS based on optical frequency domain reflectometry used in our paper is improved significantly compared to previous sensors. It has an accuracy of 0.1 and a spatial resolution of 1 mm. Therefore, the strain transfer performance of such a high-precision DOFS should be investigated further. We fixed a DOFS on a host structure using an adhesive, and the factors influencing strain transfer were studied, including the “endpoint effect,” bond length, shear modulus of the coating and adhesive layers, and thickness of the adhesive layer. A theoretical strain transfer model for a DOFS was designed and the theoretical strain transfer coefficient was calculated using numerical simulations. Furthermore, an evaluation of the theoretical model was implemented using a uniform strength beam. The experimental results are consistent with the simplified two-layer strain transfer model presented in our paper. The effect of the bond length on strain transfer is summarized from experimental and numerical simulation results, i.e., a larger adhesive length leads to a higher strain transfer coefficient and smaller “endpoint effect.” If the shear modulus of the fiber coating layer and the glue is high, we obtain a high train transfer coefficient and small “endpoint effect.” These conclusions provide a useful reference for the application of DOFS in practice.