Realization of active metamaterials with odd micropolar elasticity

TL;DR

This paper demonstrates an active metamaterial with odd micropolar elasticity using piezoelectric components and electronic control, enabling non-reciprocal mechanical behaviors and boundary-localized vibrational modes.

Contribution

It introduces a freestanding active metabeam with programmable odd elastic moduli, linking non-Hermitian topological indices to vibrational mode localization.

Findings

Active metabeam exhibits non-reciprocal bending and shearing.

The odd elastic modulus is tunable via phase control.

Vibrational modes are localized at sample boundaries.

Abstract

Materials made from active, living, or robotic components can display emergent properties arising from local sensing and computation. Here, we realize a freestanding active metabeam with piezoelectric elements and electronic feed-forward control that gives rise to an odd micropolar elasticity absent in energy-conserving media. The non-reciprocal odd modulus enables bending and shearing cycles that convert electrical energy into mechanical work, and vice versa. The sign of this elastic modulus is linked to a non-Hermitian topological index that determines the localization of vibrational modes to sample boundaries. At finite frequency, we can also tune the phase angle of the active modulus to produce a direction-dependent bending modulus and control non-Hermitian vibrational properties. Our continuum approach, built on symmetries and conservation laws, could be exploited to design others systems such as synthetic biofilaments and membranes with feed-forward control loops.