Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677
Previously [R. Hickling, J. Acoust. Soc. Am. 94, 1815(A) (1993)] computed visualizations of sound-power flow were presented that demonstrate the focusing of sound by solid spheres, as a function of frequency, for a number of different materials. In the past, fluid-filled spheres have been used to obtain focusing and to increase target strength [e.g., E. O. Belcher, Proc. Oceans 93 Conf. (Oct. 1993)]. Solid spheres, however, avoid possible leakage and are probably less susceptible to temperature change. The use of liquid-filled spheres for focusing is usually based on simple ray-refraction theory. The evaluation of solid spheres for focusing requires a greater amount of computation. Computational methods and techniques are described. Potential applications include omnidirectional passive surveillance in a half-space and beam forming using a driven system.