Acoustic one-way metasurfaces: Asymmetric Phase Modulation of Sound by Subwavelength Layer

Abstract

We theoretically design and numerically demonstrate an acoustic one-way metasurface, which is a planar and acoustically subwavelength layer behaving like a nearly-reflectionless surface with arbitrary wave-steering capability for incident wave impinging on one side, while virtually blocking the reversed wave. The underlying mechanism is based on an asymmetric phase modulation by coupling a phase array and a near-zero-index medium. We exemplify a metastructure-based implementation by combining the hybrid metastuctures and labyrinthine structures. Moreover, the performance of the proposed implementation is demonstrated via three distinct phenomena of anomalous refraction, wave splitting and conversion of propagation wave to surface wave. Our findings may offer more possibilities for sound manipulation and improve the application potential of acoustic artificial devices in situations such as ultrasonic imaging and therapy.

Acoustic metasurfaces

“…Artificial materials engineered with the asymmetric acoustic transmission characteristic may be useful for noise control and energy-harvesting applications 86 . Asymmetric sound transmission can be achieved using acoustic metasurfaces by integrating a near-zero-index metasurface (ZIM) with a gradient-index metasurface (GIM) 23,27 . A plane wave impinging normally on the GIM is deflected by an angle dictated by the generalized Snell's law (Fig.…”

Acoustic Metamaterials in Aeronautics

“…It involves allowing a sound wave to enter into a domain where it is contained and forbidden to exit, creating a sort of insulation of the exterior domain from the trapped sound. The most interesting application, in the authors' opinion, of sound trapping [63] uses a one-way metasurface, made by a layer of Helmholtz resonators with different depths attached to a near-zero index space-coiling based metamaterial (in a zero index acoustic metamaterial, the sound wave is infinitely stretched in space, and it travels with extremely high phase velocity). The functioning principle is depicted in Figure 8.…”

Continuously Tunable Acoustic Metasurface for Transmitted Wavefront Modulation

“…Inspired by their study, many researchers proposed various designs of acoustic metasurfaces with space-coiling structures and demonstrated a variety of novel features [12][13][14][15] . The space-coiling metasurface show an exceptional ability in controlling acoustic waves, including self-accelerating beam generators 15 , negative bulk modulus cell 16 , acoustic rectifiers 17,18 , optimal sound-absorbing 2 device [19][20][21] , acoustic rainbow trapping 22 , extraordinary transmission 23,24 , acoustic one-way device [25][26][27] , negative refraction 11,28 , unidirectional acoustic cloak 29,30 , and acoustic focusing [31][32][33][34] . Such metasurface functionalities are based on the dispersive wavefront modulation and the extraordinary acoustic transmission which is attributed to the interplay between Fabry-Perot resonances inside the sub-wavelength-scale channel and resonances of the surface waves propagating on the plate 31,33 .…”