Shell-type acoustic metasurface and arc-shape carpet cloak

Abstract

We systematically propose a thin shell-type acoustic metasurface, which could be used to design a carpet cloak that closely covers an arc-shaped object, therefore providing the necessary support for hiding an object with any arbitrary shape. To facilitate the experimental measurement, however, the work here starts with some rotary spherical shell-type and ellipsoidal shell-type cell structures. The measured and calculated sound transmission loss (STL) results of these structures suggest that the sound insulation performances of the shell-type structure are quite different from those of the plate-type structure, indicating a possible break in the shape of the classical sound insulation curve. Considering also that cylindrical shell structures are more widely used in practice than the rotary shell structures, a number of two-dimensional bilayer cylindrical and elliptic cylindrical shell structures were, therefore, designed in this assay. Due to the asymmetry of the structure, the shell-type cells could exhibit bianisotropic sound absorption, reflection and effective parameters. Furthermore, the stiffness of the thin shell structure changed nonlinearly with the changing of the radius of curvature, with a wing shape tendency. In addition, a bilayer cylindrical shell-type acoustic metasurface and an arc-shaped carpet acoustic cloak were successively designed, wherein the phased compensation of differently shaped cell structures could be adjusted by means of a new engineering iso-phase design method. This work could provide the necessary guidance to extend existing results in the field of membrane- and plate-type acoustic metamaterials for shell-type structures, and the realization of the arc-shaped cloak could provide support for the design of a carpet acoustical cloak for use with arbitrary shapes.

Generation of Non-aliased Two-dimensional Acoustic Vortex with Enclosed Metasurface

“…The numerical results show that such metasurface unit cell provides arbitrary phase shift within the full 2π range via adjustment of a single structural parameter while keeping a near-unity transmission efficiency (>0.99) which is ensured by the introduction of membranes (as evidence by the comparison between the cases with and without membranes) and crucial for the high-quality reproduction of target 2D NAAV. It is noteworthy that our mechanism for generating non-aliased vortex in a two-dimensional system is general and can be practically implemented by using various metastructure designs such as some other shell-type metasurfaces 34 . Here we choose to employ our designed MCHM that applies to the production of 2D vortices of different radii by simply controlling a single parameter of unit number N, which helps to significantly simplify the design and fabrication of the resulting device as long as the spatial resolution of phase profile is high enough.…”

Recent progress in acoustic metamaterials and active piezoelectric acoustic metamaterials - A review

“…The mechanism of resonant acoustic meta-atoms with deep sub-wavelength sizes relies on oscillators that generate out-of-phase responses to modify wave propagation [11,20,43,[43][44][45]. Fano interference can result in a negative effective mass density and an imaginary wave vector [11,43,[43][44][45][46]. Another strategy is to design sub-wavelength AMs with resonance-induced negative bulk modulus [47,48], such as Helmholtz resonator chains [20].…”

Tunable, reconfigurable, and programmable acoustic metasurfaces: A review

“…Thanks to their thinness which is usually in the sub-wavelength, AMs have added value and functionalities in comparison with other acoustic metamaterials with small footprint (Xie et al, 2014;Cheng et al, 2015;Zhao et al, 2017;Assouar et al, 2018;Quan and Alu, 2019). Numerous exotic acoustic phenomena such as sound cloaking (Faure et al, 2016;Ma et al, 2019;Fan et al, 2020;Zhou et al, 2020), sound splitting (Zhai et al, 2018;Ding et al, 2021), sound absorption (Ma et al, 2014;Song et al, 2019;Liu et al, 2021;Li et al, 2022a;Guo et al, 2022), anomalous reflection or refraction (Diaz-Rubio and Tretyakov, 2017;Li et al, 2019a;Zhu and Lau, 2019;Li et al, 2020a;Chiang et al, 2020;Song et al, 2021), sound focusing (Zhu et al, 2016a;Lombard et al, 2022), one-way sound propagation (Zhu et al, 2015;Jiang et al, 2016), and medical ultrasound (Tian et al, 2017;Hu et al, 2022) have been proposed and demonstrated using AMs. AMs possess unusual features, including selective focusing and negative refraction, are enabled by the generalized Snell's law, which adds a new degree of freedom to control the behavior of transmitted or reflected waves by incorporating a lateral momentum (Yu et al, 2011) (see Figure 1).…”