Abstract

Experimental Investigations on Parametric Antenna Operation in Granular Materials

V.Tournat, V.Aleshin, B.Castagnede (Laboratoire d'Acoustique de l'Universite du Maine, Le Mans, France); V.E.Gusev (Laboratoire de Physique de l'Etat Condense UMR-CNRS, Universite du Maine, Le Mans, France)

e-mail: vincent.tournat@univ-lemans.fr

Experimental results obtained in unconsolidated granular materials are presented (glass beads of 0.1mm or 2mm diameter). An important feature of such media, compared to homogeneous media, is the occurrence of wave scattering when the wavelength becomes comparable to a characteristic size of the micro-structure (bead diameter). Wave scattering leads to mode conversion between compression and shear waves, and, under some conditions, leads to diffusion of acoustic waves. We present results in a regime of operation where pump waves are strongly scattered. The process of self-demodulation in the case of pump waves diffusion is similar to thermal expansion caused by phonon conductivity in solids. Wide band demodulated secondary signals are compared to a numerical fit of a three dimensional model to obtain characteristic parameters of the acoustic waves transport in the medium. We also observed self-demodulation of shear pump waves into both shear and compression secondary waves. The efficiency of the self-demodulation process from shear into compression waves and the polarization dynamics of shear waves are used to determine the level of coherence of the pump waves field.

Section : 3