Three-Dimensional Trapping and Assembly of Small Particles with Synchronized Spherical Acoustical Vortices

Three-dimensional harmless contactless manipulation and assembly of micro-objects and microorganisms would open other horizons in microrobotics and microbiology, e.g., for microsystems assembly or tissue engineering. In this paper, we theoretically show that small particles compared to the wavelength can be trapped and assembled in three dimensions with synchronized spherical vortices. The particles can be approached both laterally and axially and, for each configuration, the maximum assembly speed can be determined by balancing the Stokes' drag force and the critical radiation force. These theoretical results provide guidelines to design acoustical tweezers able to trap and assemble particles in three dimensions.