Modeling of Fiber Optic Acoustic Coupler for Ultrasonic Sensing

Abstract

Fiber Bragg grating sensors have been applied in the remote-bonding configuration for structural health monitoring, in which ultrasonic modes are propagated along the optical fiber to the sensor. Recently, coupling of the ultrasonic mode from optical fiber to optical fiber through an adhesive coupler has also been demonstrated. This paper develops a finite element (FE) model to describe the coupler behavior as a function of the fiber and coupler properties, for future optimization of couplers. The FE model is validated with previous experimental data. We also compare the FE model to three theoretical models (spring and damper frictional contact models and coupled mode theory). The results show that the FE model and spring well replicate the experimental results. Future work will use the resulting FE and spring models to derive solutions for the coupling coefficient as a function of the geometrical and material parameters of the coupler.