RESONANCES OF DEFORMED GAS-BUBBLES IN LIQUIDS

A T-matrix expansion technique has been used to investigate the monopole acoustical resonances of bubbles deformed into elongated axisymmetric objects (specifically: prolate spheroids and cylinders with hemispherical endcaps). The bubbles are modeled as air-filled inclusions in water. Scattering occurs because of the change of acoustical impedance at the interface between the two media. The results confirm that the resonance frequency of a bubble increases when it is deformed from a spherical shape. It increases more quickly with aspect ratio for cylindrical than for prolate spheroidal bubbles. The resonance frequency is also independent of the direction of excitation. For both cylindrical and prolate spheroidal bubbles the frequency width of the resonance increases with the deformation; but the corresponding values of Q fall more quickly for the cylindrical bubble. The scattering amplitude also decreases with the deformation, especially for endfire incidence. The angular distribution of acoustic scattering changes with the shape of the bubble. For spheroidal bubbles there is relatively little change from the spherical pattern obtained with an undeformed bubble; but for cylindrical bubbles the scattering may be irregular, with pronounced lobes in the broadside direction. © 1994, Acoustical Society of America. All rights reserved.