Diffusive transport and Anderson localization of ultrasonic waves in strongly scattering inhomogeneous media

In inhomogeneous media with constituents having very different acoustic properties, very strong multiple scattering of ultrasonic waves can occur, especially when the wavelength is comparable with the length scales over which the constituent properties vary. Such strong multiple scattering can lead to a long “coda” that dominates the observable behaviour in pulsed experiments, and can dwarf the ballistic pulse that travels coherently through the medium. In many cases, the transport of energy by the multiply scattered waves can be well described using the diffusion approximation, which may even seem quite surprising since all interference effects are ignored. An exception occurs when the return probability that the waves scatter back to the same spot becomes enhanced as a result of very strong multiple scattering; then interference plays an important role and can ultimately lead to Anderson localization and the breakdown of wave propagation. Examples of these wave phenomena will be presented in contrasting...