Wavefront modulation and subwavelength diffractive acoustics with an acoustic metasurface

Abstract

Metasurfaces are a family of novel wavefront-shaping devices with planar profile and subwavelength thickness. Acoustic metasurfaces with ultralow profile yet extraordinary wave manipulating properties would be highly desirable for improving the performance of many acoustic wave-based applications. However, designing acoustic metasurfaces with similar functionality to their electromagnetic counterparts remains challenging with traditional metamaterial design approaches. Here we present a design and realization of an acoustic metasurface based on tapered labyrinthine metamaterials. The demonstrated metasurface can not only steer an acoustic beam as expected from the generalized Snell's law, but also exhibits various unique properties such as conversion from propagating wave to surface mode, extraordinary beam-steering and apparent negative refraction through higher-order diffraction. Such designer acoustic metasurfaces provide a new design methodology for acoustic signal modulation devices and may be useful for applications such as acoustic imaging, beam steering, ultrasound lens design and acoustic surface wave-based applications.

Single-sensor multispeaker listening with acoustic metamaterials

“…In the past, acoustic metamaterials with high anisotropy (14,15), extreme nonlinearity (16), or negative dynamic parameters (density, bulk modulus, refractive index) (17)(18)(19)(20) have been realized. Applications such as scattering reducing sound cloak (21,22), beam steering metasurface (23), and other wave manipulating devices (24)(25)(26)(27) have been proposed and demonstrated. We demonstrate here that acoustic metamaterials can also be useful for encoding independent acoustic signals coming from different spatial locations by creating highly frequency-dependent and spatially complex measurement modes (28), and aid the solution finding for the inverse problem.…”

High transmission acoustic focusing by impedance-matched acoustic meta-surfaces

“…Space-coiling structures have been utilized in the design of gradient acoustic lenses. [6][7][8][9][10] With gradient acoustic lenses, acoustic radiation patterns, such as focusing, 6,[8][9][10][11] tunable transmission, 7,12,13 reflection, 10 and cylindrical-to-plane wave conversion, 9 can be manipulated. Very recently, acoustic meta-surfaces have been used in the design of acoustic lenses.…”

Full-angle negative reflection realized by a gradient acoustic metasurface

“…11,12 However, because of the asymmetrical reflection angle distribution of the reflected gradient metasurface, the negative reflection realized by such gradient metasurface that shown in Figure 1(b) is totally different from the wide-angle negative reflection that realized by the phononic crystal 27 and the negative reflection phenomena discussed in other works. 28,29 Recently, Xie, Y. et al 16 reported the apparent negative refraction on a transmissive gradient acoustic metasurface when the incident angle is beyond the critical angle and pointed out that supercell periodicity has play an critical role when analyzing the wave manipulation behaviors of the gradient acoustic metasurface. The apparent negative refracted angle can be calculated by the generalized law of refraction that modified by an additional reciprocal lattice vector term.…”

“…Similar to their electromagnetic counterparts, acoustic meta-atoms with desired phase shift can be realized by tuning the acoustic impedance values of the meta-atoms. Various types of acoustic meta-atoms have been designed, such as coiling-up space structures, [13][14][15] tapered labyrinthine subunits, 16,17 zigzag slits, 18 split-spheres, 19 Helmholtz resonator arrays 20 and membrane based structures. 21 And the acoustic metasurfaces composed by these building blocks are able to operate as powerful compact acoustic wavefront manipulation devices, such as planar acoustic lens, 22,23 special acoustic beam generator 14,24 and acoustic carpet cloaking.…”