Effective model of fiber Bragg gratings for simulation of ultrasonic guided wave measurements using spectral finite elements

This paper deals with the modeling of optical fiber Bragg gratings (FBGs) dedicated to ultrasound measurements. It addresses the problem of modeling the impact of acoustic waves on such small transducers, with typical FBG lengths and optical fiber diameters several orders of magnitude smaller than the ultrasound's characteristic wavelength, especially with guided waves. The method adopted to model the behavior of such transducers can therefore severely affect computational performances and results. We propose here the use of a one-way coupling scheme, limiting the impact on the simulation of ultrasonic waves, while reproducing accurately the FBG transducer's response. This model is validated against experimental data, especially regarding the FBG's spectral response with respect to ultrasonic wavelength.