Perfect Acoustic-Vortexes Constructed by the Fourier Transform of Quasi-Bessel Beams Based on the Simplified Ring Array of Sectorial Planar Transducers.

ABSTRACT

Benefiting from the independence of the vortex radius on the topological charge (TC), the perfect acoustic-vortex (PAV) with an angular phase gradient exhibits important perspectives in acoustic applications. However, the practical implementation is still restricted by the limited accuracy and flexibility of the phase control for large-scaled source arrays. An applicable scheme of constructing PAVs by the spatial Fourier transform of quasi-Bessel AV (QB-AV) beams is developed using the simplified ring array of sectorial transducers. The principle of PAV construction is derived based on the phase modulation of the Fourier and saw-tooth lenses. Numerical simulations and experimental measurements are carried out for the ring array with the continuous and discrete phase spirals. The construction of PAVs is demonstrated by the annuli at an almost identical peak pressure with the vortex radius independent of the TC. The vortex radius is proved to increase linearly with the increase of the rear focal length and the radial wavenumber, which are determined by the curvature radii and the acoustic refractive index of the Fourier lens and the bottom angle of the saw-tooth lens, respectively. The improved PAV with a more continuous high-pressure annulus and lower concentric disturbances can be constructed by the ring array of more sectorial sources and the Fourier lens of a bigger radius. The favorable results demonstrate the feasibility of constructing PAVs by the Fourier transform of QB-AV beams and provide an implementable technology in the fields of acoustic manipulation and communication.