Acoustic orbital angular momentum capture and detection via gradient spoof-fluid-spoof waveguides

Acoustic orbital angular momentum (OAM), with its unique helical wavefront structure and orthogonality, offers innovative technical approaches for fields, such as acoustic communication, particle manipulation, and acoustic imaging. However, the efficient capturing, separation, and accurate detection of acoustic vortex remain a core bottleneck that hinders their practical utilization. Here, we propose a compact OAM-capturing device based on a cylindrical spoof-fluid-spoof waveguide with gradient groove depths, which enables precise modulation of the dispersion behavior of acoustic vortices of different OAM modes through an axially linear gradient in groove depth. Within the operating frequency band, acoustic vortices with different topological charges l = 1, 2, 3 are successively captured at distinct spatial positions along the waveguide axis. This device features a compact structure, operates without external control, and offers considerable design flexibility, providing a passive solution for the efficient detection and separation of acoustic vortices. It shows promising potential for applications in acoustic communication, signal recognition, and ventilated sound insulation.