Resonance scattering of sound by a small gaseous object of arbitrary form

Abstract

The acoustic scattering amplitude for a dilute gaseous object of arbitrary form in a liquid medium is determined self-consistently for the case of linear dimension small as compared to the wavelength. A scatterer of bulk modulus β, and density p, in a medium of bulk modulus II and density p may exhibit monopole resonance scattering at a frequency w,= (4πβoC / pV)l, in which V is the volume and C is the capacitance in electrostatic units of a conducting replica of the scatterer. The criterion for occurrence of the resonance phenomenon is 3Fβo/β <<«1, in which the shape factor F = 4πC3 / 3V> 1 is minimum for a sphere. Dipole scattering is given in terms of the polarizability dyadic of a nonconducting replica of dielectric constant p/po, and is negligibly small in a neighborhood of the resonance frequency.