# Acoustic metamaterials with spinning components

## TL;DR

This paper demonstrates that an array of spinning cylinders can create unique acoustic metamaterials with folded bands, one-way interface states, and tunable properties due to rotation-induced effects, promising advanced control over sound propagation.

## Contribution

It introduces a novel acoustic metamaterial design with spinning components, revealing unusual band structures and robust one-way sound transport mechanisms.

## Key findings

- Folded bulk and interface-state bands in subwavelength regime.
- Zero-frequency gap appears beyond a critical filling fraction.
- Robust one-way transport of interface states demonstrated numerically.

## Abstract

Using both multiple scattering theory and effective medium theory, we find that an acoustic metamaterial consisting of an array of spinning cylinders can possess a host of unusual properties including folded bulk and interface-state bands in the subwavelength regime. The folding of the bands has its origin in the rotation-induced antiresonance of the effective compressibility with its frequency at the angular velocity of the spinning cylinders, as well as in the rotational Doppler effect which breaks the chiral symmetry of the effective mass densities. Both bulk and interface-state bands exhibit remarkable variations as the filling fraction of the spinning cylinders is increased. In particular, a zero-frequency gap appears when exceeds a critical value. The uni-directional interface states bear interesting unconventional characteristics and their robust one-way transport properties are demonstrated numerically.

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Source: https://tomesphere.com/paper/1905.07170