A LASER-BASED INVESTIGATION OF HIGHER-ORDER MODES IN TRANSIENT LAMB WAVES

This Letter describes the integration of laser and fiber optic methods for generating and detecting broadband, transient Lamb waves in a steel plate. The generated Lamb waves are shown to be a superposition of different Lamb modes including the zeroth-order symmetric together with the zeroth- and first-order antisymmetric modes. Signal processing techniques are used to extract the phase velocities for each of these modes over a continuous, broadband frequency spectrum from the transient time histories of the waves recorded at two locations on a steel plate. The results are found to be in excellent agreement with theoretical phase velocities for each of the three modes evaluated.