Achromatic metasurfaces with inversely customized dispersion for ultra-broadband acoustic beam engineering

TL;DR

This paper introduces ultra-broadband achromatic acoustic metasurfaces capable of arbitrary wave manipulation across wide frequency ranges, overcoming narrow-band limitations of traditional designs through topology optimization.

Contribution

The study presents a novel design approach for broadband achromatic metasurfaces with record bandwidths, enabling versatile acoustic wave control beyond existing narrow-band capabilities.

Findings

Achieved record-breaking relative bandwidths of 93.3%, 120%, and 118.9% for different functionalities.

Demonstrated functionalities include beam steering, focusing, and levitation.

Revealed mechanisms such as internal resonances, bi-anisotropy, and multiple scattering underpinning broadband dispersion.

Abstract

Metasurfaces, the ultrathin media with extraordinary wavefront modulation ability, have shown versatile potential in manipulating waves. However, existing acoustic metasurfaces are limited by their narrow-band frequency-dependent capability, which severely hinders their real-world applications that usually require customized dispersion. To address this bottlenecking challenge, we report ultra-broadband achromatic metasurfaces that are capable of delivering arbitrary and frequency-independent wave properties by bottom-up topology optimization. We successively demonstrate three ultra-broadband functionalities, including acoustic beam steering, focusing and levitation, featuring record-breaking relative bandwidths of 93.3%, 120% and 118.9%, respectively. All metasurface elements show novel asymmetric geometries containing multiple scatters, curved air channels and local cavities. Moreover, we reveal that the inversely designed metasurfaces can support integrated internal resonances, bi-anisotropy and multiple scattering, which collectively form the mechanism underpinning the ultra-broadband customized dispersion. Our study opens new horizons for ultra-broadband high-efficiency achromatic functional devices on demand, with promising extension to the optical and elastic achromatic metamaterials.