Scattering of focused ultrasonic beams by two spherical cavities in close proximity.

Ultrasonic fields generated by one and two spherical cavities placed in front of a point-focused acoustic lens are modeled by the semi-analytical distributed point source method (DPSM). Results are generated by properly considering the interaction effect between two cavities placed in the focused ultrasonic field. The interaction effect between the two cavities prohibits the linear superposition of single cavity solutions to obtain the solution for two cavities placed in close proximity. Therefore, although some analytical and semi-analytical solutions are available for the single cavity in a focused ultrasonic field, those solutions cannot be simply superimposed for solving the two-cavity problem even for a linear elastic material. Solution of this problem is necessary to evaluate when two cavities placed in close proximity can be distinguished by an acoustic lens and when it is not possible. The comparison between the reflections of ultrasonic energy from two small cavities versus a single big cavity is also investigated.