Generation of acoustic helical wavefronts using metasurfaces

Abstract

It has been shown that acoustic waves with helical wavefronts can carry angular momentum, which can be transmitted towards a propagating medium. Such a wave field can be achieved by using a planar array of electroacoustic transducers, forming a given spatial distribution of phased sound sources which produce the desired helical wavefronts. Here, we introduce a technique to generate acoustic vortices, based on the passive acoustic metasurface concept. The proposed metasurface is composed of space-coiled cylindrical unit cells transmitting sound pressure with a controllable phase shift, which are arranged in a discretized circular configuration, and thus passively transforming an incident plane wavefront into the desired helical wavefront. This method presents the advantage of overcoming the restrictions on using many acoustic sources, and it is implemented with a transmitting metasurface which can be easily three-dimensionally printed. The proposed straightforward design principle can be adopted for easy production of acoustic angular momentum with minimum complexity and using a single source.

Orbital Angular Momentum Waves: Generation, Detection, and Emerging Applications

“…In this section, we discuss various state-of-the-art methods for generating OAM in the fields of light, radio, and sound waves. Because of the Cylindrical lenses [1], [11] Spiral phase plates (SPPs) [12] Holographic gratings [13]- [15] Spatial light modulators (SLMs) [16], [17] Metamaterials [20]- [24] Liquid crystal q-plates [25], [26] Spiral phase plates (SPPs) [29]- [31], [35], [36] Spiral reflectors [33], [34] Holographic gratings [32] Uniform circular antenna arrays (UCAAs) [2], [8], [37]- [41] Metamaterials [44]- [49] Dielectric q-plates [50] Spiral phase plates (SPPs) [51], [52] Uniform circular transducer arrays (UCTAs) [4], [55]- [58] Spiral diffraction gratings [59]- [62] Metamaterials [64]- [66] Optical OAM Radio OAM Acoustic OAM large number of methods discussed, Fig. 2 shows a diagram that summarizes a taxonomy of the techniques presented in this section.…”

“…Recently, an active spiral grating fabricated using a cellular ferroelectret film has been proposed to improve conversion efficiency [63]. In addition to optical OAM and radio OAM, metamaterial can also be used to generate acoustic OAM [64]- [66]. Usually, to generate acoustic OAM a metasurface with sub-wavelength thickness is equally divided into N regions.…”

Sharkskin-Inspired Magnetoactive Reconfigurable Acoustic Metamaterials

“…Furthermore, the concept of the active acoustic metamaterials enabled by magnetoactive structures may be extended to design various switchable acoustic metadevices. For example, the magnetoactive elastomers can be used to design twisted helicoids to design orbital angular momentum metastructures [57] which can be tuned on and off via magnetically modulating the axial lengths. As another example, magnetoactive acoustic tunneling may be realized by assembling magnetoactive Mie resonator arrays into the tunnel, thus enabling actively switching between the tunneling with supercoupling and regular wave guiding [58].…”

Acoustic metasurfaces

“…5d) can produce a metasurface with a first-order acoustic vortex with spiral phases and orbital angular momentum. Other set-ups have been proposed 28,[95][96][97] , and applications of acoustic vortices have been studied [98][99][100][101][102] .…”