# Non-reciprocal robotic metamaterials

## TL;DR

This paper introduces a new class of robotic mechanical metamaterials that achieve broadband, tunable, and attenuation-free non-reciprocal wave transmission through local control loops, surpassing previous limitations near resonances or nonlinearities.

## Contribution

It presents a novel design of robotic metamaterials with local control loops that enable broadband non-reciprocal wave propagation, a significant advancement over existing narrowband or resonance-limited methods.

## Key findings

- Achieved 50dB non-reciprocal isolation over 3.5 decades in frequency.
- Demonstrated tunable, broadband, and attenuation-free non-reciprocal performance.
- Observed one-way amplification of pulses.

## 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 only in the vicinity of resonances or using nonlinearities, thereby nonreciprocal transmission remains limited to narrow ranges of frequencies or input magnitudes and sensitive to attenuation. Here, we devise a novel type of 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 that first-of-their-kind asymmetric standing waves at all frequencies and unidirectionally amplified propagating waves emerge. We demonstrate experimentally and numerically that this property leads to tunable, giant, broadband and attenuation-free non-reciprocal performances, namely a level of 50dB non-reciprocal isolation over 3.5 decades in frequency, as well as one-way amplification of pulses.

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Source: https://tomesphere.com/paper/1903.03807