Three-dimensional trapping and assembly of small particles with synchronized spherical acoustical vortices

TL;DR

This paper demonstrates theoretically that synchronized spherical acoustical vortices can be used to trap and assemble micro-objects in three dimensions, extending previous 2D methods based on cylindrical vortices.

Contribution

It introduces a theoretical framework for 3D particle trapping and assembly using synchronized spherical acoustical vortices, overcoming limitations of previous 2D approaches.

Findings

Particles can be trapped in 3D with spherical vortices.

Maximum assembly speed is determined by balancing forces.

Design guidelines for 3D acoustical tweezers are provided.

Abstract

Three-dimensional harmless contactless manipulation and assembly of micro-objects and micro-organisms would open new horizons in microrobotics and microbiology, e.g. for microsystems assembly or tissue engineering. In our previous work [Gong and Baudoin, Phys. Rev. Appl., 12: 024045 (2019)], we investigated theoretically the possibility to trap and assemble in two dimensions small particles compared to the wavelength with synchronized acoustical tweezers based on cylindrical acoustical vortices. However, since these wavefields are progressive along their central axis, they can only push or pull (not trap) particles in this direction and hence are mainly limited to 2D operations. In this paper, we extend our previous analysis and show theoretically that particles can be trapped and assembled in three-dimensions with synchronized spherical vortices. We show that the particles can be approached both laterally and axially and we determine the maximum assembly speed by balancing the Stokes' drag force and the critical radiation force. These theoretical results provide guidelines to design selective acoustical tweezers able to trap and assemble particles in three dimensions.