Separation of Lamb Wave Modes Using Remotely Bonded Seven-Core Fiber Bragg Grating Fabry-Pérot Interferometer

This paper presents the use of a seven-core optical fiber with fiber Bragg grating (FBG) pairs written into each core to identify the amplitudes of symmetric vs. antisymmetric Lamb waves traveling in a structure. The FBG pairs form Fabry-Perot interferometers to measure the amplitudes of the propagating waves in each fiber core. The magnitudes of the longitudinal and flexural modes in the optical fiber are then calculated from these amplitudes. An experimental demonstration of the calculation of the longitudinal and flexural mode amplitudes in the optical fiber is presented from the core modes. The relative phase delay between cores is also applied to better measure the amplitude of the flexural mode. The results are compared to independent measurements of the mode amplitudes in the fiber using a 3D micro-laser Doppler vibrometer.