Acoustic second-harmonic generation with shear to longitudinal mode conversion in granular mediaV. Tournat1, V. E. Gusev1, V. Yu. Zaitsev2 and B. Castagnède1
1 Université du Maine - Av. Olivier Messiaen, 72085 Le Mans Cedex 9, France
2 Institute of Applied Physics - 46 Uljanova Street, Nizhny Novgorod, 603950 Russia
(Received 20 August 2003; accepted in final form 15 April 2004)
Excitation of longitudinal acoustic wave at the 2nd harmonic by sinusoidal shear acoustic wave in a granular material is reported. The amplitude of the 2nd harmonic exhibits beatings (typical of nonlinear processes in dispersive media), which are observed not as a function of the distance from emitter, but with increasing amplitude of the primary (pump) shear wave. The effect is attributed to varying contribution of clapping intergrain contacts to the total nonlinearity of the medium with increasing pump amplitude, which modifies the effective length of the nonlinear interaction. This is consistent with the idea that in granular assemblages there is an important amount of contacts loaded much weaker than in average.
43.25.+y - Nonlinear acoustics.
83.80.Fg - Granular solids.
81.05.Rm - Porous materials; granular materials.
© EDP Sciences 2004