Breaking the fundamental limit of space-coiling metamaterial: Toward simultaneous phase and amplitude modulation

Abstract

Acoustic metasurfaces represent a family of planar, wavefront-shaping devices garnering increasing attention due to their capacity for novel acoustic wave manipulation. Despite the successful demonstration of phase engineering using metasurfaces, amplitude modulation remains overlooked. This work explores the feasibility of simultaneous phase and amplitude modulation using space-coiling metamaterials. In the case of conventional space-coiling metamaterials, we observed a fundamental bound on the transmission coefficient, which precludes full wavefront manipulation. Herein, we present a novel class of metasurfaces featuring a modified space-coiling structure and enabling full acoustic control with simultaneous phase and amplitude modulation. The functionality of this class of metasurfaces, featuring a gradient in channel spacing, has been theoretically and numerically investigated and an equivalent model simplifying the structural behavior is presented. Furthermore, a metasurface featuring this novel geometry has been designed and its functionality in modifying acoustic radiation patterns simulated. The class of acoustic metasurface demonstrated in this work provides a new design methodology enabling complete acoustic wave manipulation, which may find utility in a range of applications including biomedical imaging, acoustic communication and non-destructive testing.