Sound Scattering from a Fluid Sphere

The scattering of sound from a spherical fluid obstacle of size comparable to a wave-length is considered, neglecting dissipation. Calculations of the acoustic pressure and the total energy in the scattered wave are presented graphically; sound velocities and densities of the sphere lie between 0.5 and 2.0 times that of the external medium. The limiting cases of Rayleigh scattering and scattering from a fixed rigid sphere are also shown for comparison. In the region where the diameter of the sphere is comparable to a wave-length, the scattering is a complicated function of frequency, showing in some cases large maxima and minima. The amplitude of the scattered wave in the backward direction from a fluid sphere a few wave-lengths in diameter exceeds twice that from a rigid sphere of the same size for the case of the sound velocity 0.8 and density equal to that of the surrounding medium.