Non-reciprocal robotic metamaterials

Martin Brandenbourger,Xander Locsin,Corentin Coulais,Edan Lerner

doi:10.1038/s41467-019-12599-3

Martin Brandenbourger, Xander Locsin + Show 2 more

Open Access

https://doi.org/10.1038/s41467-019-12599-3

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Journal: Nature Communications	Publication Date: Oct 10, 2019
Citations: 271	License type: open-access

Affiliation: University of Amsterdam

Abstract

Non-reciprocal transmission of motion is potentially highly beneficial to a wide range of applications, ranging from wave guiding to shock and vibration damping and energy harvesting. To date, large levels of non-reciprocity have been realized using broken spatial or temporal symmetries, yet mostly in the vicinity of resonances, bandgaps or using nonlinearities, thereby non-reciprocal transmission remains limited to narrow ranges of frequencies or input magnitudes and sensitive to attenuation. Here, we create a robotic mechanical metamaterials wherein we use local control loops to break reciprocity at the level of the interactions between the unit cells. We show theoretically and experimentally that first-of-their-kind spatially asymmetric standing waves at all frequencies and unidirectionally amplified propagating waves emerge. These findings realize the mechanical analogue of the non-Hermitian skin effect. They significantly advance the field of active metamaterials for non hermitian physics and open avenues to channel mechanical energy in unprecedented ways.

Highlights

Non-reciprocal transmission of motion is potentially highly beneficial to a wide range of applications, ranging from wave guiding to shock and vibration damping and energy harvesting
While breaking reciprocity has been a long-standing challenge in electromagnetics, there has been over the last few years an explosion of interest for breaking reciprocity in optical[4,5,6,7] and micro[8] waves without magnetic fields, and beyond electromagnetism, i.e., in acoustics[9], quantum systems[10,11], and mechanics[12,13], creating new tools to engineer a novel generation of devices and materials that guide, damp, or control energy and information
These strategies have led to large levels of nonreciprocal isolations, but with input magnitudes or input frequencies that are limited to narrow ranges, and are sensitive to attenuation

Summary

Introduction

Non-reciprocal transmission of motion is potentially highly beneficial to a wide range of applications, ranging from wave guiding to shock and vibration damping and energy harvesting. Non-reciprocity has been achieved by using passive structures combining broken spatial symmetries and nonlinearities[13,14] and using active time-modulated components that break time-reversal symmetry[3,12,15,16,17] These strategies have led to large levels of nonreciprocal isolations, but with input magnitudes or input frequencies that are limited to narrow ranges, and are sensitive to attenuation. This work builds on the field of active metamaterials, yet with a key new twist: while active metamaterials only have actuating elements, robotic metamaterials include a combination of local sensing, computation, communication, and actuation As a result, they feature unique wave phenomena, namely asymmetric modes at all frequencies and unidirectional amplification, and in turn realize large, broadband, linear, and self-amplified nonreciprocal transmission of mechanical waves. These findings realize the classical counterpart of the so-called non-Hermitian skin effect[23,24,25,26,27,28]

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