Ultrasonic Lamb wave mode conversion to optical fiber guided mode with varying input conditions

In structural health monitoring (SHM) applications, one of the advantages of utilizing a surface bonded fiber Bragg grating (FBG) sensor for damage detection is its increased sensitivity in collecting ultrasonic waves. Recent studies have demonstrated that for a certain bonding condition the output FBG response can be increased by bonding the optical fiber at a distance away from the FBG to collect optical fiber guided wave (L-01 mode) that is converted from S-0 Lamb wave, referred as remote bonding. However in order to apply the remote bonding configuration in practical situations, the So mode conversion to L-01 mode through an adhesive bond under various conditions must be characterized. This work investigates how the coupled L-01 mode changes with varying input S-0 mode frequency and angle of incidence through an adhesive bond. The goal of this work is to better understand the S-0 mode conversion to the L-01 mode in order to implement the remote bonding configuration for an improved SHM of a structure.