Investigation of surface acoustic wave propagation on a sphere using laser ultrasonics

Clorennec, D.; Royer, D.
September 2004
Applied Physics Letters;9/20/2004, Vol. 85 Issue 12, p2435
Academic Journal
Using the noncontact laser ultrasonic technique, we investigate the propagation of surface acoustic waves on a sphere (SSAW). A finite thermoelastic line source gives rise to combined focusing and reversal effects. As for propagation on a cylinder surface, the reversal of the SSAW pulse is explained by the dispersion of the high frequency components of the laser-generated acoustic pulse. The focusing effect, due to the curvature of the surface, depends on the angular aperture of the source. From diffraction theory, optimal conditions for diffraction free propagation are derived, both in harmonic and pulse regimes. On a steel sphere of radius 25 mm, Rayleigh waves excited by a 20 ns YAG laser pulse focused onto a 3 mm line propagate with a nearly constant amplitude.


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