Characterization of scatterer motion in a reverberant medium

Abstract

Recently, an acoustic technique has been proposed to measure the scattering strength and the dynamics of weak moving scatterers in a reverberant cavity: diffusing reverberant acoustic wave spectroscopy (DRAWS). Both parameters are obtained from the correlations of the reverberated-scattered transient pressure fields for different scatterers positions. This technique is based on a diffusive field theory [de Rosny et al., Phys. Rev. Lett., 90, 094302 (2003)]. Here, a more systematic approach of the DRAWS technique properties is presented. Moreover, an important extension is proposed using the fourth-order moment of the field, or the variance of the correlation estimator. Contrary to the correlations (second-order moment) that allow the measurement of the scattering cross section, its variance (fourth-order moment) is shown to be mainly sensitive to the scatterer displacement. The robustness of DRAWS is discussed using different configurations: a computer simulation of a moving scatterer in a two-dimensional cavity. Experiments were also carried out with a 23-mm-diameter copper sphere moved by stepping motors in 16liters of water, and finally a human walking in a 125-m3 reverberant room.