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 ste el plate. The generated Lamb waves are shown to be a superposition of different Lamb modes including the zeroth-order symmetric together wit h the zeroth- and first-order antisymmetric modes. Signal processing t echniques are used to extract the phase velocities for each of these m odes over a continuous, broadband frequency spectrum from the transien t time histories of the waves recorded at two locations on a steel pla te. The results are found to be in excellent agreement with theoretica l phase velocities for each of the three modes evaluated.