Abstract
Metasurfaces based on geometric phase acquired from the conversion of the optical spin states provide a robust control over the wavefront of light, and have been widely employed for construction of various types of functional metasurface devices. However, this powerful approach cannot be readily transferred to the manipulation of acoustic waves because acoustic waves do not possess the spin degree of freedom. Here, we propose the concept of acoustic geometric-phase meta-array by leveraging the conversion of orbital angular momentum of acoustic waves, where well-defined geometric-phases can be attained through versatile topological charge conversion processes. This work extends the concept of geometric-phase metasurface from optics to acoustics, and provides a new route for acoustic wave control.
Highlights
We propose an acoustic meta-array based on acoustic geometric phases which are obtained through versatile acoustic vortex topological charge (TC) conversion occurring within each pixel of the meta-array—a cylindrical acoustic waveguide with judiciously engineered interior structures
A geometric phase arises from the conversion between two different orbital angular momenta, which can be continuously controlled by varying the orientation of the conversion element, i.e., the acoustic geometric meta-plates (AGM) for the designated TC conversion process
We show that this geometric phase accompanies a conversion process between different orbital angular momenta, and the same principle can be applied to acoustics where spin degree of freedom does not exist
Summary
We propose an acoustic meta-array based on acoustic geometric phases which are obtained through versatile acoustic vortex topological charge (TC) conversion occurring within each pixel of the meta-array—a cylindrical acoustic waveguide with judiciously engineered interior structures. Each meta-pixel waveguide, containing a number of acoustic geometric meta-plates (AGM), is designed to implement sequential manipulations on the incident acoustic wave including generation and conversion of vortex beams of various TCs. A geometric phase arises from the conversion between two different orbital angular momenta, which can be continuously controlled by varying the orientation of the conversion element, i.e., the AGM for the designated TC conversion process.
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