No abstract

Acoustic metasurfaces represent a family of planar wavefront-shaping devices garnering increasing attention due to their capacity for novel acoustic wave manipulation. By precisely tailoring the geometry of these engineered surfaces, the effective refractive index may be modulated and, consequently, acoustic phase delays tuned. Despite the successful demonstration of phase engineering using metasurfaces, amplitude modulation remains overlooked. Herein, we present a class of metasurfaces featuring a horn-like space-coiling structure, enabling acoustic control with simultaneous phase and amplitude modulation. The functionality of this class of metasurfaces, featuring a gradient in channel spacing, has been investigated theoretically and numerically and an equivalent model simplifying the structural behavior is presented. A metasurface featuring this geometry has been designed and its functionality in modifying acoustic radiation patterns experimentally validated. This class of acoustic metasurface provides an efficient design methodology enabling complete acoustic wave manipulation, which may find utility in applications including biomedical imaging, acoustic communication, and non-destructive testing.

Recently, with advances in acoustic metamaterial science, the possibility of sound attenuation using subwavelength structures, while maintaining permeability to air, has been demonstrated. However, the ongoing challenge addressed herein is the fact that among such air-permeable structures to date, the open areas represents only small fraction of the overall area of the material. In the presented work, in order to address this challenge, we firstly demonstrate that a transversely-placed bilayer medium with large degrees of contrast in the layers' acoustic properties exhibits an asymmetric transmission, similar to the Fano-like interference phenomenon. Next, we utilize this design methodology and propose a deep-subwavelength acoustic metasurface unit cell comprising nearly 60% open area for air passage, while serving as a high-performance selective sound silencer. Finally, the proposed unit cell performance is validated experimentally, demonstrating a reduction in the transmitted acoustic energy of up to 94%. This ultra-open metamaterial (UOM) design, leveraging a Fano-like interference, enables high-performance sound silencing in a design featuring a large degree of open area, which may find utility in applications in which highly efficient, air-permeable sound silencers are required, such as smart sound barriers, fan or engine noise reduction, among others.

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.