Analysis of surface acoustic wave propagation on a cylinder using laser ultrasonics

This letter shows an unexpected phenomenon for surface acoustic waves (Rayleigh waves) propagating on a solid cylinder. It was observed that a short Rayleigh wave pulse was reversed during its propagation. In experiments on duraluminum and steel cylinders, transient surface acoustic waves were launched by a pulsed YAG laser focused along a line. The radial component of the displacement was measured by a heterodyne optical interferometer. The wave forms recorded versus the angle θ between the source and the detection point shows that the Rayleigh pulse, which is monopolar (positive) near the source, becomes bipolar at θ=45° and monopolar (negative) at θ=90°. An analytical calculation taking into account the dispersive effect reproduces wave forms whatever the propagation distance. A physical model is proposed to account for the reversal of the acoustic pulse.