Attenuation in suspensions of irregularly shaped sediment particles: A two-parameter equivalent spherical scatterer model

Results are presented from an acoustic attenuation spectroscopy study of suspensions of irregularly shaped sediment particles and of nominally spherical lead-glass beads. The measured spectra cover a wide frequency band of 1-100 MHz. It is shown that the spectra can be brought into close agreement with the rigid movable sphere model using two equivalent sphere size parameters. One parameter is the diameter d(G) of an equal cross-sectional area sphere, and is used to scale the frequency to obtain the nondimensional size/frequency parameter ka. The other parameter is the diameter d(p) of an equal volume sphere, and is used to scale the particle volume to obtain the particle number density N. It was observed that for the irregular particles the attenuation for ka > 1 is enhanced with respect to the sphere case. The observed enhancement factors are considerable: up to 1.6 for natural sand particles and 1.8 for the most irregular particles studied (ground quartz). In terms of the two-parameter model the enhancement factor is equal to a shape parameter b(0) = (d(G)/d(p))(3) and can indeed be explained as a shape effect. The implications of this result for the acoustic detection of suspended sediments in aqueous environments are discussed. (C) 1997 Acoustical Society of America.