Sound vortex diffraction via topological charge in phase gradient metagratings.

Area of Science:

• Acoustics
• Metasurfaces
• Wave physics

Background:

• Orbital angular momentum (OAM) in wave fields is extensively studied using metasurfaces.
• Acoustic OAM is typically generated via phase twisting in engineered metasurfaces.
• Current methods for sound vortex manipulation are limited, necessitating advanced techniques.

Purpose of the Study:

• To propose and theoretically investigate a diffraction mechanism for manipulating sound vortices.
• To develop a generalized sound vortex diffraction law based on topological charge conservation.
• To experimentally validate the proposed mechanism and its application in acoustic devices.

Main Methods:

• Theoretical derivation of a sound vortex diffraction law using the generalized conservation principle of topological charge.
• Numerical simulations to confirm the theoretical predictions of sound vortex diffraction.
• Design and experimental verification of a phase gradient metagrating (PGM) using Helmholtz resonators.

Main Results:

• A novel sound vortex diffraction law was theoretically revealed and numerically validated.
• The PGM demonstrated asymmetric transmission of sound vortices.
• The diffraction mechanism provides enhanced control over sound vortex manipulation.

Conclusions:

• The proposed diffraction mechanism offers a powerful new method for manipulating sound vortices.
• Phase gradient metagratings can be designed for advanced control of acoustic OAM.
• This research opens new avenues for versatile OAM-based acoustic device design.