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

Abstract

Two-dimensional (2D) acoustic vortex allows new physics and applications different from threedimensional counterparts, yet existing mechanisms usually have to rely on active array composed of transducers which may result in complexity, high cost and, in particular, undesired spatial aliasing effect. We propose to generate 2D acoustic vortex inside an enclosed metasurface illuminated by axisymmetric wave carrying no orbital angular momentum. We derive the criterion on unit size for eliminating spatial aliasing effect which is challenging for conventional active approaches and design a membrane-based metasurface to implement our mechanism. The performance of our strategy is demonstrated via precise production of different orders of non-aliased vortices regardless of center-to-center alignment, with undistorted Bessel-like pattern extending to the whole inner region. We anticipate our design with simplicity, compactness, precision and flexibility to open up possibility to design novel vortex devices and find important applications in diverse scenarios such as on-chip particle manipulations.

Controlling acoustic orbital angular momentum with artificial structures: From physics to application

“…4(a)) with advantages in terms of simplicity, resolution, efficiency, compactness, and energy consumption. [55] They rigorously derived the boundary conditions for generating the desired mode of 2D acoustic vortex without aliasing, which is implemented by designing subwavelength unit cells with phase engineering capability and high transmission efficiency. Figure 7(a) shows the performance of their scheme to precisely generate a nonaliasing 2D vortex by using a compact, passive device, as evidence by the undistorted Bessel-like pattern extending to the whole inner region.…”

“…7. Schematics of various types of mechanisms for 2D OAM production: (a) a circular metasurface for generating non-aliasing 2D OAMs; [55] (b) generating a 2D acoustic vortex on an unbounded surface; [56] (c) efficient 2D OAM conversion by bianisotropic metasurface; [57] (d) schematic plot of the passive acoustic parity-time-symmetric ring cavity for generating 2D acoustic vortex; [58] (e) virtual boundary transformation and simulated normalized acoustic pressure of 2D vortex distribution inside a pentagram region. [60] Panels (a)-(e) are reproduced with permission from Refs.…”

Metamaterial-based real-time communication with high information density by multipath twisting of acoustic wave

“…More importantly, the OAM multiplexing 12 – 15 strategies rely on multiple coaxially-overlapped twisted beams used as orthogonal communication channels, while leaving the potential of non-coaxial beams to further boost acoustic communication efficiency unexplored. In such cases, the channel number has to be increased by including more high-order OAM modes, leading to more severe diffraction and spatial aliasing effect, which limit the maximum number of available communication channels 16 – 18 . Although the possibility of information multiplexing/demultiplexing based on non-coaxial OAM beams has been proven in optics 19 – 22 , it is not feasible to directly translate the same mechanism to acoustics considering the fact that complicated equalization algorithm 23 – 25 based on time-consuming computation is needed for counteracting the diffraction-induced crosstalk effect which is much stronger for acoustic waves.…”