Reflected wavefront manipulation based on ultrathin planar acoustic metasurfaces

Abstract

The introduction of metasurfaces has renewed the Snell's law and opened up new degrees of freedom to tailor the optical wavefront at will. Here, we theoretically demonstrate that the generalized Snell's law can be achieved for reflected acoustic waves based on ultrathin planar acoustic metasurfaces. The metasurfaces are constructed with eight units of a solid structure to provide discrete phase shifts covering the full 2π span with steps of π/4 by coiling up the space. By careful selection of the phase profiles in the transverse direction of the metasurfaces, some fascinating wavefront engineering phenomena are demonstrated, such as anomalous reflections, conversion of propagating waves into surface waves, planar aberration-free lens and nondiffracting Bessel beam generated by planar acoustic axicon. Our results could open up a new avenue for acoustic wavefront engineering and manipulations.

Wavefront modulation and subwavelength diffractive acoustics with an acoustic metasurface

“…However, mapping the success of electromagnetic metasurfaces to the acoustic domain is challenging, mostly due to the mechanical nature and distinct properties of acoustic waves. Some initial theoretical exploration 7,8 has recently been shown, nevertheless, only limited experimental investigations have been demonstrated 9 .…”

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.…”

Focusing and directional beaming effects of airborne sound through a planar lens with zigzag slits

“…Similar design strategies have been widely employed to design optical metasurfaces with great flexibility in tailoring wavefronts [21][22][23][24], such as redirecting the propagation of incident waves. Recently, analogous studies have been extended to sound waves [25][26][27][28]. However, so far there is no such focusing lens realized for transmitted sound waves.…”

“…It is of interest that the planar lens presented here also exhibits an excellent conversion from a Below we demonstrate that a nonuniform array of ZSs can minic the above secondary sources retrived from the reverse design. Recently, the ZS units have been extensively employed to design acoustic metamaterials [9][10][11]19,20] and metasurfaces [25][26][27][28] due to the flexibility in tailoring the propagation length of sound. As illustrated in Fig.…”