Anomalous wave reflection from the interface of two strongly nonlinear granular media

TL;DR

This paper reports the first experimental observation of a dramatic change in wave reflectivity at the interface of two nonlinear granular media, induced by magnetic precompression, resembling an acoustic diode effect.

Contribution

It introduces the first experimental evidence of a nonlinear wave reflection phenomenon controlled by magnetic precompression in granular media.

Findings

Observed a dramatic change in wave reflectivity at the interface.

Identified the effect as an acoustic diode phenomenon.

Numerical simulations explain the high velocity gradient near the interface.

Abstract

Granular materials exhibit a strongly nonlinear behaviour affecting the propagation of information in the medium. Dynamically self-organized strongly nonlinear solitary waves are the main information carriers in granular chains. Here we report the first experimental observation of the dramatic change of reflectivity from the interface of two granular media triggered by a noncontact magnetically induced initial precompression. It may be appropriate to name this phenomenon the "acoustic diode" effect. Based on numerical simulations, we explain this effect by the high gradient of particle velocity near the interface.