An annulus acoustic metasurface (AAM) composed of composite labyrinthine structure (CLS) subunits has been well designed to generate fractional acoustic vortices (FAVs) in air. The FAVs with different topological charges (TCs) are realized by modulating the transmitted phase shifts through the CLS subunits. The evolution of the pressure field and phase distributions of the FAV is investigated numerically using the finite element method and demonstrated theoretically. As TC increases from 1 to 2, the central phase singularity first splits into two phase singularities and then gradually merges into a higher-order phase singularity. Meanwhile, the corresponding pressure field distribution first evolves from the annular intensity pattern to two discontinuous parts and then gradually recovers to the annular ring distribution with larger radius. We further find that the FAV generated by the AAM could extend to a relatively long distance. Finally, experiments are performed to verify the FAV by the AAM and demonstrate its long-distance propagation. The airborne FAVs by the AAMs may find potential applications in micro-particle manipulation, acoustic communication, and edge-detection imaging.

Artificial structure plates engraved with discrete Archimedean spiral slits have been well designed to achieve fractional acoustic vortices (FAVs). The phase and pressure field distributions of FAVs are investigated theoretically and demonstrated numerically. It is found that the phase singularities relating to the integer and fractional parts of the topological charge (TC) result in dark spots in the upper half of the pressure field profile and a low-intensity stripe in the lower half of the pressure field profile, respectively. The dynamic progress of the FAV is also discussed in detail as TC increases from 1 to 2. With increasing TC from 1 to 1.5, the splitting of the phase singularity leads to the deviation of the phase of the FAV from the integer case and hence a new phase singularity occurs. As TC m increases from 1.5 to 2, two phase singularities of the FAV approach together and finally merge as a new central phase singularity. We further perform an experiment based on the Schlieren method to demonstrate the generation of the FAV.

Multiplexing technology with increased information capacity plays a crucial role in the realm of acoustic communication. Different quantities of sound waves, including time, frequency, amplitude, phase, and orbital angular momentum (OAM), have been independently introduced as the physical multiplexing approach to allow for enhanced communication densities. An acoustic metasurface is decorated with carbon nanotube patches, which when electrically pumped and set to rotate, functions as a hybrid mode‐frequency‐division multiplexer with synthetic dimensions. Based on this spatiotemporal modulation, a superposition of vortex beams with orthogonal OAMs and symmetric harmonics are both numerically and experimentally demonstrated. Also, flexible combinations of OAM modes with diverse frequency shifts are obtained by transforming the azimuthal phase distributions, which inspires a mode‐frequency‐division multiplexing approach that significantly promotes the communication capacity.

BHMR sample and verify the enhanced monopole and dipole acoustic antennas experimentally.