Acoustic carpet cloak based on an ultrathin metasurface

Abstract

An acoustic metasurface carpet cloak based on membrane-capped cavities is proposed and investigated numerically. This design has been chosen for allowing ultrathin geometries, although adapted to airborne sound frequencies in the range of 1 kHz (λ ≈ 30 cm), surpassing the designs reported in the literature in terms of thinness. A formulation of generalized Snell's laws is first proposed, mapping the directions of the incident and reflected waves to the metasurface phase function. This relation is then applied to achieve a prescribed wavefront reflection direction, for a given incident direction, by controlling the acoustic impedance grading along the metasurface. The carpet cloak performance of the proposed acoustic metasurface is then assessed on a triangular bump obstacle, generally considered as a baseline configuration in the literature.

Apparent Negative Reflection with the Gradient Acoustic Metasurface by Integrating Supercell Periodicity into the Generalized Law of Reflection

“…Numerous types of acoustic meta-atoms have been proposed to construct the functional acoustic metasurfaces, such as tapered labyrinthine structure14, coiling-up slit structure1516, zigzag channel17, Helmholtz resonator array18, split sphere19 and membrane based structure20. Based on these acoustic meta-atoms, a great number of acoustic wavefront manipulation devices have been constructed and operated successfully, for example, the acoustic focusing lens2122, acoustic vortex beam generator23, acoustic Airy beam generator2425, acoustic carpet cloaking2627 and so on.…”

Multi-frequency acoustic metasurface for extraordinary reflection and sound focusing

“…AMs have the ability to manipulate acoustic wavefront freely to realize various functionalities, such as extraordinary reflection and sound focusing, [2][3][4][5][6][7][8] non-diffraction beams, 9-11 vortex, 12,13 one-way manipulation, [14][15][16][17][18] and cloaking. [19][20][21] However, the conventional AMs always work in a single frequency due to the resonance effect. The breakthrough in frequency band may extend the practical applications.…”

Concentric artificial impedance surface for directional sound beamforming

“…4 In addition, the concept of artificial impedance surfaces can be applied to acoustics by utilizing acoustic metasurfaces. [5][6][7][8][9][10][11][12] For example, a periodic array of Helmholtz resonators can be used to manipulate the reflection phase of incident sound waves. 6,7,10,11 In contrast to highimpedance electromagnetic surfaces, these resonant surfaces are regarded as series LC resonators.…”