Ultrasonic wave transport in weakly confined granular media in the intermediate frequency regime

Stéphane Job , Anatoliy Strybulevych , John H. Page

We present preliminary experimental observations of ultrasonic wave transport in non-cohesive randomly close packed granular media under low confinement pressures, near the unjamming transition. Our samples are 10-mm-thick and 165‐mm‐diameter slabs made of 1.25-mm-diameter aluminium spheres (monodisperse sample), eventually mixed with 0.9-mm-diameter borosilicate spheres (bidisperse sample). The slabs are covered by thin plastic sheets, which allow maintaining a partial vacuum (0.1 to 0.9 atm) in the samples. Wave transport is investigated over a wide frequency range (25 kHz to 1 MHz) by analyzing the coherent ballistic transmitted field (phase and group velocities, attenuation and scattering mean free path) and the incoherent multiply scattered coda [JH Page et al., Phys. Rev. E, 52, 3106 (1995)]. We find that the time-of-flight intensity profile of the coda is independent of frequency over a wide range of frequencies for which the wavelength is comparable with the sizes of the scatterers. This suggests a plateau in the diffusion coefficient, as predicted by Vitelli and co-workers [Phys. Rev. E 81, 021301 (2010)]. At higher frequencies, the intensity profile becomes progressively confined spatially, providing evidence for the approach to Anderson localization of ultrasonic waves in the medium [Hu et al., Nature Phys. 4, 945, (2008)].

Domaines: Acoustique [physics.class-ph]

Stéphane Job, Anatoliy Strybulevych, John H. Page. Ultrasonic wave transport in weakly confined granular media in the intermediate frequency regime. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00811269⟩