Ultrasound propagation in disordered granular media

Abstract

ABSTRACTWe have identified, according to the ratio of the wavelength to the grain size, two distinct types of pulsed ultrasound transmission through a dry bead packing under stress: one corresponds to coherent ballistic waves characterized by the effective medium description, the other to the waves scattered by the inhomogeneous stress field within the granular medium. Over long distances of transport, the multiply scattered waves exhibit a diffusive character. Also we investigate the dynamics of the granular medium during a compaction under cyclic loading-unloading. Both the macroscopic deformation and the microscopic rearrangement have been measured, via an ultrasonic correlation technique using the multiple acoustic scattering very sensitive to the change of the system configuration. It is found that as the packing fraction increases, there is a continuous evolution of the system in response to external loading, from an irreversible behavior towards more elastic one.