Demonstrating a Bi-directional Asymmetric Frequency Conversion in Nonlinear Phononic Crystals

TL;DR

This paper introduces a bi-directional asymmetric frequency conversion mechanism in nonlinear phononic crystals, enabling tunable wave manipulation through nonlinear contact and spatial asymmetry, with potential applications across various physical systems.

Contribution

It demonstrates, both numerically and experimentally, a novel wave transport mechanism in granular crystals that achieves tunable, bi-directional frequency conversion beyond traditional uni-directional methods.

Findings

Successful experimental validation of bi-directional frequency conversion.

Demonstration of tunable wave manipulation via nonlinear contact and spatial asymmetry.

Potential for broad application in nonlinear physical domains.

Abstract

Beyond the constraints of conservative systems, altering wave propagation frequency emerges as a crucial factor across diverse physical domains. This Letter demonstrates bi-directional asymmetric frequency conversion -- either upward or downward -- depending on the excitation direction in the elastic domain, moving beyond uni-directional approaches. We numerically and experimentally demonstrate its practical realization in a model system of cylindrical beam crystals, a type of granular crystal characterized by intrinsic local resonance. This novel wave transport mechanism operates through the interplay of nonlinear contact, spatial asymmetry, and the coupling of local resonance. Thanks to the proposed highly tunable architecture, we demonstrate various ways to manipulate wave transport, including tunable frequency conversion. Given that the local resonance we employ exemplifies avoided crossings (i.e., a strong coupling effect), our work may inspire investigations into diverse physical nonlinear domains that support material/structural resonance.