Low-Channel-Count Thermoacoustic Multi-Ring Array for Radially Shaped Acoustic Orbital Angular Momentum Beams

This paper proposes a low-channel-count thermoacoustic multi-ring array framework for generating radially shaped acoustic orbital angular momentum (OAM) beams. The aim is to enable radial shaping of a separable OAM aperture without independently driving every element.

The framework combines a radial-azimuthal separable aperture with the square-law heat generation of a DC-biased thermoacoustic element. Ringwise DC biases set the radial weights, whereas azimuthal AC phases impose the helical OAM phase. The AC-DC cross term in Joule heating forms their product locally and produces the required acoustic weight. An electro-thermo-acoustic finite element method (FEM) model of a single element verifies the first-harmonic amplitude and phase control. The FEM-derived equivalent complex-pressure boundary condition is then incorporated into a multi-ring acoustic propagation model.

Array-level simulations with uniform and Laguerre-Gaussian-like (LG-like) radial envelopes show that the proposed shared-drive architecture can change the radial field structure while preserving the prescribed azimuthal OAM topology. For this separable aperture class, the required controls are reduced from MN elementwise amplitude-and-phase controls to M ringwise DC biases and N azimuthal AC phase controls.

The study shows that local AC-DC mixing in a DC-biased thermoacoustic element can realize outer-product aperture weights, enabling low-channel radial shaping of acoustic OAM fields.