Detection of fundamental shear horizontal mode in plates using fibre Bragg gratings

Shear horizontal guided waves are attractive for structural health monitoring applications in view of the non-dispersive behaviour of the fundamental mode, possibly higher frequencies of operation and a less complex multi-modal structure. One of the key issues with the deployment of shear horizontal guided waves of modes for structural health monitoring applications is the general non-availability of techniques to sense this family of modes effectively. This article demonstrates the detection of fundamental shear horizontal waves in an aluminium plate by placing a fibre Bragg grating along a direction perpendicular to that of propagating guided elastic waves. In order to uniquely identify the three fundamental plate-guided modes, we map the experimentally measured group velocities as detected by the fibre Bragg grating to theoretically obtained group velocity dispersion curves. We find that the experimentally measured group velocity values using time-of-flight measurements from a perpendicularly placed fibre Bragg grating are in agreement with the theoretical curve for the S H 0 mode. Possible extension of these results to feature-guided modes is also discussed.