Experimental Observation of Nonreciprocal Waves in a Resonant Metamaterial Beam

TL;DR

This paper demonstrates an elastic metamaterial that uses stiffness variations in resonators to induce temporal modulation, breaking time-reversal symmetry and achieving nonreciprocal wave dispersion without external motion.

Contribution

It introduces a novel elastic metamaterial design that exploits internal stiffness variations for nonreciprocal wave control through temporal modulation.

Findings

Successfully demonstrated nonreciprocal wave dispersion in experiments.

Achieved tilt of dispersion modes via internal stiffness modulation.

Validated breaking of time-reversal symmetry in the metamaterial.

Abstract

Space-time-varying materials pledge to deliver nonreciprocal dispersion in linear systems by inducing an artificial momentum bias. Although such a paradigm eliminates the need for actual motion of the medium, experimental realization of space-time structures with dynamically changing material properties has been elusive. In this letter, we present an elastic metamaterial that exploits stiffness variations in an array of geometrically phase-shifted resonators -- rather than external material stimulation -- to induce a temporal modulation. We experimentally demonstrate that the resulting bias breaks time-reversal symmetry in the resonant metamaterial, and achieves a nonreciprocal tilt of dispersion modes within dynamic modulation regimes.