Diffusive transport of acoustic waves in strongly scattering media

The diffusive transport of multiply scattered ultrasonic waves is investigated experimentally and theoretically in a simple system consisting of glass beads in water. New experimental results are presented using a novel method for measuring the frequency correlation function of the transmitted acoustic field. The wave diffusion coefficient D is found to vary strongly with frequency when the wavelength is comparable to the size of the scatterers, reflecting a substantial slowing down of wave propagation when the scattering is strongest. The results are interpreted using a model based on a spectral function approach that gives good agreement with experiment. (C) 1999 Elsevier Science B.V. All rights reserved