Wavefront manipulation based on transmissive acoustic metasurface with membrane-type hybrid structure

Abstract

We designed and demonstrated a gradient acoustic metasurface to manipulate the transmissive wavefront. The gradient metasurface is composed of eight elements based on membrane-type hybrid structures, whose thickness and width are about 1/5 and 1/20 of the incident wavelength, respectively. Here, we employ acoustic theory to analyze the transmission spectrum and phase gradient of the metasurface, the properties of high transmission efficiency and discrete phase shifts over the full range can be achieved simultaneously. By appropriate selection of the phase profile along the transverse coordinate of the metasurface or the angle of incident wave, the transmissive wavefront manipulations based on metasurface can be obtained as expected from the generalized Snell’s law, such as anomalous refraction, acoustic cloak based on flat focusing, acoustic self-bending beam, conversion of propagating wave to surface wave and negative refraction. Our gradient metasurface may have potential application in low-loss acoustic devices.

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

“…Hence our design uses the coupling of two resonant membranes at two sides to improve the impedance matching with the background media, resulting in a near-unity transmission efficiency. The underlying physical mechanism is that membranes with resonance frequency being tuned to be identical with the MCHM produce an additional acoustic reactance such that we can compensate for the impedance mismatch in inner structure [31][32][33] . The structural parameters are chosen as: H = L = λ/3 < λ/e, t = λ/100, a = 1.25t, w = 4t, and d = t/8 respectively.…”

Recent progress in acoustic metamaterials and active piezoelectric acoustic metamaterials - A review

“…Their unusual acoustic properties and functionalities are usually induced by sub-wavelength space coiling channels [12,52,53] or highly resonant inclusions [54][55][56][57][58]. The deep sub-wavelength structures enable acoustic wave manipulation through spatial phase gradient shifts, which can be achieved by space coiling elements [12,52,53], Helmholtz resonators [54][55][56][57][58], resonant membranes and plates [59][60][61], or porous materials [62][63][64][65]. For instance, space coiling structures can slow down the acoustic wave speed inside AMs to achieve large refractive indices and desired spatial phase gradients, broadening their operating bandwidth and avoiding resonance-induced energy dissipation [12,52,53].…”

“…To manipulate the transmitted acoustic wavefront, a membrane-type acoustic metasurface, which consists of membrane resonators with different side slit thicknesses, as shown in Figure 6(b), can generate transmitted phase shifts covering the full 2𝜋 span as shown in Figure 6(c) [60]. As a result, anomalous phenomena, including abnormal sound transmission, acoustic self-bending beam, propagating-to-surface wave conversion, and acoustic focusing [59][60][61], can be observed in numerical simulations and experiments. Besides, a double-membrane acoustic metasurface was constructed with an air cavity sealed by two elastic membranes, as shown in Figure 6(d) [61].…”

Improving directional radiation quality based on a gradient amplitude acoustic leaky wave antenna

“…which is equivalent to a series resonant circuit comprised of an acoustic resistance R , am acoustic mass m am and acoustic capacitance C am [31,32]. By considering airmembrane interactions, the air section of the straight pipe can be described by a circuit consisting of a series acoustic mass m d d w…”