Axially focused (glory) scattering from surface waves on spheroids: Model and experimental confirmation using a brass spheroid.

Solid spheres in water illuminated by ultrasound can display enhanced backscattering due to an axially focused scattering contribution. One of the mechanisms for producing the needed outgoing toroidal wavefront is the launching and guiding of a leaky Rayleigh-like wave around the surface of the sphere [K. L. Williams and P. L. Marston, J. Acoust. Soc. Am. 78, 722-728 (1985)]. A related backscattering enhancement was also demonstrated for spherical shells [S. G. Kargl and P. L. Marston, J. Acoust. Soc. Am. 85, 1014-1028 (1989)]. The present research demonstrates that a similar backscattering enhancement is detectable for axisymmetric ultrasonic illumination of a solid prolate brass spheroid. By using short tone burst illumination, the axially focused contribution to the scattering is distinguishable from the specular reflection and other contributions to the scattering. The evidence for the Rayleigh wave mechanism is seen in the timing of this contribution and bistatic measurements: experimental and theoretical predictions are supportive. This research supports surface-guided ray theory for variable curvature objects in water.