ASA 126th Meeting Denver 1993 October 4-8

3aAO2. Resonance scattering from nonspherical bubbles in water.

C. Feuillade M. F. Werby

Naval Res. Lab., Stennis Space Center, MS 39529-5004

Submerged bubbles can be treated as air-filled inclusions in water from which scattering occurs because of the change of acoustical impedance at the interface between the two media. The T-matrix expansion technique allows for the general description of scattering from both spherically and nonspherically shaped bubbles. This method is used to study the monopole acoustical resonances of bubbles deformed into elongated axisymmetric objects (specifically, prolate spheroids and cylinders with hemispherical endcaps). The results confirm that the resonance frequency of a bubble increases when it is deformed from a spherical shape, but show that it is also independent of the direction of excitation and increases more quickly with aspect ratio for cylindrical than for prolate spheroidal bubbles. The frequency width of the resonance increases with the deformation in both cases, but Q falls more quickly for the cylindrical bubble. Increasing the deformation causes the scattering amplitude to decrease and its angular distribution to change. A remarkable result is that for highly deformed spheroidal bubbles there is relatively little change from the spherical scattering pattern obtained with an undeformed bubble. In contrast, highly deformed cylindrical bubbles show prominent lobes. [Work supported by ONR Technology Directorate (Element 602435N) and by the Naval Research Laboratory, 6.1 Program (Element 601153N). Technical management provided by NRL--SSC.]