Enhanced Backscattering and Modal Echo of Reverberant Elastic Waves

Abstract

We report experimental evidence for coherent backscattering of waves in a three-dimensional elastic body. Ultrasonic spectral energy density consequent to a transient excitation is measured as a function of time and of distance from the source. In accord with the predictions of random matrix theory, an enhancement is found near the source by a weak localization factor of 2 at early times, but a factor of 3 at late times. The effect appears to be independent of absorption.