ANDERSON LOCALIZATION OF ULTRASOUND

Incoherent transport of ultrasound is studied in two dimensions in the sub-MegaHertz range in an inhomogeneous 30 centimeter square aluminum plate. The spectral energy density associated with the higher frequencies is found to be governed by a diffusion equation, in accordance with classical predictions. The elastodynamic energy at the lower frequencies, however, where wavelengths are comparable to microscale, is observed to be transported with greatly diminished efficiency. This absence of transport is ascribed to Anderson localization of the normal modes of vibration. Localization lengths at least as short as 10 cm, or about 20 times larger than the microscale are observed. An anomalous very slow transport over length scales beyond the localization length is also observed. © 1990.