Polar metamaterials: A new outlook on resonance for cloaking applications

TL;DR

This paper introduces polar metamaterials with rotational resonance that enable elastic cloaking, demonstrating their potential to achieve transformation-invariant properties and cloaking in elastodynamics.

Contribution

It presents a novel design of polar and chiral metamaterials using rotational resonance, advancing transformation elastodynamics for cloaking applications.

Findings

Rotational resonance induces polar and chiral behaviors in metamaterials.

Numerical cloaking performance is satisfactory under pressure and shear waves.

The work bridges transformation elastodynamics with acoustics and optics.

Abstract

Rotationally resonant metamaterials are leveraged to answer a longstanding question regarding the existence of transformation-invariant elastic materials and the ad-hoc possibility of transformationbased passive cloaking in full plane elastodynamics. Combined with tailored lattice geometries, rotational resonance is found to induce a polar and chiral behavior; that is a behavior lacking stress and mirror symmetries, respectively. The central, and simple, idea is that a population of rotating resonators can exert a density of body torques strong enough to modify the balance of angular momentum on which hang these symmetries. The obtained polar metamaterials are used as building blocks of a cloaking device. Numerical tests show satisfactory cloaking performance under pressure and shear probing waves, further coupled through a free boundary. The work sheds new light on the phenomenon of resonance in metamaterials and should help put transformation elastodynamics on equal footing with transformation acoustics and optics.