Acoustical particle conveyors via Bessel-beam superposition

Abstract

We proposed an on-axis, multi-bottle beam by superposing two coaxial acoustic Bessel beams to produce acoustical particle conveyors. The spatial acoustic pressure distribution and source phase, determined solely by lateral wavenumber $k_r$ and the radius of the circular source, were derived to establish a theoretical basis for precise ultrasound field control. These conveyors exploit strong-gradient acoustic radiation forces at acoustic bottles, enabling stable trapping of micrometer-scale Rayleigh particles in free space. By fine-tuning the incident acoustic frequency, our acoustic tweezers can trap, push, and pull multiple particles along the propagation axis. We discussed the optimization of $k_r$-dependent phase lens, focusing on the selection of $k_r$ values and the number of simultaneously emitting Bessel beams, which improves field observation and enhances trapping stability. The system employs only a single acoustic source and a phase lens, offering potential for cell manipulation and targeted medical treatments in vivo.