An examination of the spherical scatterer approximation in aqueous suspensions of sand

The available data for scattered acoustic intensity and attenuation in dilute aqueous suspensions of sand are compared with theory. In theoretical calculations, the scatterer is assumed to be spherical and elastic, or rigid and movable, or rigid and immovable. The rigid movable model provides the best fit to the data. The failure of the elastic model in comparison to the rigid sphere models indicates that resonance excitation does not occur in natural sand grains, probably because of irregularities in shape. The fact that better agreement with experiment is obtained with the rigid movable model than with the rigid immovable model indicates that the inertia of the particles is important. Additional approximate expressions for the form factor and attenuation coefficient have been constructed based on a modified form of the so-called high-pass model introduced by Johnson [J. Acoust. Soc. Am. 61, 275–277 (1977)]. The modified high-pass model provides a fit to the data that is as good as, or better than, the rigid movable case.