Proof of concept of a frequency-preserving and time-invariant metamaterial-based nonlinear acoustic diode

A S Gliozzi,F Bosia,B Morvan,M Scalerandi,N M Pugno,A O Krushynska,M Miniaci

doi:10.1038/s41598-019-44843-7

Abstract

Acoustic filters and metamaterials have become essential components for elastic wave control in applications ranging from ultrasonics to noise abatement. Other devices have been designed in this field, emulating their electromagnetic counterparts. One such case is an acoustic diode or rectifier, which enables one-way wave transmission by breaking the wave equation-related reciprocity. Its achievement, however, has proved to be rather problematic, and current realizations display a number of shortcomings in terms of simplicity and versatility. Here, we present the design, fabrication and characterization of a device able to work as an acoustic diode, a switch and a transistor-like apparatus, exploiting symmetry-breaking nonlinear effects like harmonic generation and wave mixing, and the filtering capabilities of metamaterials. This device presents several advantages compared with previous acoustic diode realizations, including versatility, time invariance, frequency preserving characteristics and switchability. We numerically evaluate its efficiency and demonstrate its feasibility in a preliminary experimental realization. This work may provide new opportunities for the practical realization of structural components with one-way wave propagation properties.

Highlights

In acoustics as well as in electromagnetism, the invariance of the wave equation under time inversion leads to the fundamental property of reciprocity, i.e. symmetrical wave propagation between two points in space, independently of which is the source and which is the receiver
We propose the realization of an Acoustic Diode (AD), based on the use of linear phononic crystals and elastic metamaterials, embedded between elastic nonlinear regions
We have presented numerical and experimental results demonstrating the feasibility of an acoustic diode based on alternating nonlinear elastic and metamaterial frequency-filtering regions, with time-invariant, frequency preserving characteristics

Summary

Introduction

In acoustics as well as in electromagnetism, the invariance of the wave equation under time inversion leads to the fundamental property of reciprocity, i.e. symmetrical wave propagation between two points in space, independently of which is the source and which is the receiver. Recent studies have shown how structural instabilities induced in “static” mechanical metamaterials can be exploited to achieve highly nonlinear dynamic response that can be tailored to requirements[28,29] and how weakly nonlinear monoatomic lattice chains can provide active control on elastic waves in phononic crystals[30] These or other approaches can be exploited to generate the type of nonlinearity required to violate spatial reciprocity in elastic wave propagation[31]. Besides its functionality as a diode, the device can be activated or deactivated at will for other applications, transforming it into a switch with the additional possibility to tune the amplitude of the output signal These characteristics are in general not concurrently present in other AD designs that exploit nonlinearity to break the propagation symmetry and to transfer energy from the fundamental to the harmonics, with a frequency variation from input to output. We recall that wave mixing occurs when two longitudinal waves propagating through a nonlinear elastic zone interact and generate another longitudinal wave with a frequency given by the difference (and sum) of the frequencies of the two original waves

Methods

Results

Conclusion