High-efficiency anomalous splitter by acoustic meta-grating

Abstract

As an inversely designed artificial device, metasurface usually means densely arranged meta-atoms with complex substructures. In acoustics, those meta-atoms are usually constructed by multi-folded channels or multi-connected cavities of deep sub-wavelength feature, which limits their implementation in pragmatic applications.We propose here a comprehensive concept of a perfect anomalous splitter based on an acoustic meta-grating. The beam splitter is designed by etching only two or four straight-walled grooves per period on a planar hard surface. Different from the recently reported reflectors or splitters, our device can perfectly split an incident wave into different desired directions with arbitrary power flow partition. In addition, because ultrathin substructures with thin walls and narrow channels are avoided in our design procedure, the proposed beam splitter can be used for waves with much shorter wavelength compared to the previous suggested systems. The design is established by rigorous formulae developed under the framework of the grating theory and a genetic optimization algorithm. Numerical simulation and experimental evidence are provided to discuss the involved physical mechanism and to give the proof-of-concept for the proposed perfect anomalous acoustic splitter.

Deep learning enables accurate sound redistribution via nonlocal metasurfaces

“…When an incident acoustic plane wave along with −y direction impinges on the metasurface (i.e., incident angle θ i = 0 • ), the periodicity of the metasurface will give rise to a set of different diffraction modes. According to the coupled mode theory, the pressure field p(x, y) and normal velocity field v(x, y) in the region above the structure (Region I) can be expressed by 40 p I (x, y)…”

Metaclusters for the Full Control of Mechanical Waves

“…It follows from the definition of S in (14) and Graf's addition theorem for Bessel functions, Eq. (9.1.79) of Abramowitz and Stegun, 20 that S † S simplifies to S † S αβ = ∞ n=−∞ J n (kR α )J n (kR β )e in(θα−θ β ) = J 0 (kR αβ )…”

“…However, the design process is still complex and functionality is limited to the control of the propagation direction of waves. [13][14][15] In this work, we present a generalization of the concept of a metagrating but for finite structures. The objective is to show how, for a given incident field, we can obtain a cluster of scatterers and their physical properties such that the scattered field presents a pre-selected shape.…”

Nonlocal acoustic metasurface for ultrabroadband sound absorption

“…Nonlocality can be seen as a more exact theoretical description of the effective medium, that considers nonlocal responses from transverse coupling. Drawing inspiration from their optical counterparts, recently, the mechanism of nonlocal metasurface has been extended to acoustics [16][17][18][19], which take advantages of the nonlocal response due to the transverse coupling between adjacent acoustic metastructure unit cells. This physical mechanism is completely different from the one on which are based conventional acoustic metasurfaces.…”