Continuously Tunable Acoustic Metasurface for Transmitted Wavefront Modulation

Abstract

Previously reported acoustic metasurfaces that consist of fixed channels, are untunable to meet the broadband requirement and alterable functionalities. To overcome this limitation, we propose screw-and-nut mechanism of tunability and design a type of continuously tunable acoustic metasurface with unit components of helical cylinders which are screwed into a plate. The spiral channel length can be tuned continuously by the screwed depth; and then a metasurface with continuously tunable acoustic phase at independent pixels is attained. Different distributions of the unit components can shape an arbitrary metasurface profile. We also developed an approximate equivalent medium model to predict the tunability of the unit component.As an example, we present the design details of a circular tunable metasurface for three-dimensional acoustic focusing of different airborne sound sources in a wide frequency region. A sample of the metasurface is manufactured by poly lactic acid (PLA) plastic with the helical cylinders being 3D-printed. Experiments of sound focusing are performed. It is shown that the results of the equivalent medium model, the finite element simulation and the experiments are in a good agreement.

Reconfigurable curved metasurface for acoustic cloaking and illusion

“…Attempts to this end, little research has been done on the tunable acoustic metasurface [28][29][30][31][32][33][34][35].…”

“…Each unit cell of this metasurface was composed of a straight channel and five shunted Helmholtz resonators, which can be tuned by a fluidic system. For the space coiling metasurface, Zhao et al [33] designed a continuously tunable acoustic metasurface with individual unit components of a helix screwed inside a cylindrical thin plate for transmitted axial 3D focusing. The idea was then extended to 2D multifunction switching of a tunable metasurface [34].…”

“…From the above discussions, the ways to overcome the restriction of fixed and rigid acoustic metasurfaces with single or narrow band are to design a lossy structure or multilayer metasurfaces [28][29][30], or an independently adjustable unit [31][32][33][34][35] to change the formed geometry. Here, in the present work, a successful concept of a tunable metasurface for carpet cloak is proposed based on a type of helical units using matched screw-and-nut physical mechanism.…”

Acoustic Metamaterials in Aeronautics

“…Coiled-up space devices and resonant membranes were intrinsically designed to lead to metasurfaces, and hence, the majority of the so-based work presented in previous paragraphs classifies as metasurfaces, due to their deep sub-wavelength thickness. However, for each of the approaches presented above, some engineered metasurfaces can be found in the literature [31][32][33][34][35]. A very interesting superabsorber with micro-bubble insertions was presented in [36].…”

Acoustic Metamaterials in Aeronautics

“…Coiling-up space devices and resonant membranes were intrinsically designed to lead to metasurfaces, and hence the majority of the so-based work presented in previous paragraphs were classifiable as metasurfaces for their deep sub-wavelength thickness. However, for each of the approach presented above, some metasurfaces engineering can be found in literature [31][32][33][34][35]. A very interesting superabsorber with micro-bubble insertions is presented in [36], a significantly sub-wavelength attenuation of sound is shown due to resonance of the bubbles in a soft elastic matrix, breaking the mass density law (which states that the amplitude of transmittance for a solid panel is proportional to the inverse of the product of the density and the thickness of the panel and the frequency of the acoustic perturbation.)…”