[Invited] Three-dimensional trapping and assembly with synchronized spherical acoustical vortices
Résumé
Micro-objects and micro-organisms trapping and assembly with acoustical tweezers would open new horizons in microrobotics and microbiology, e.g., selective cells fusion and aggregation. Our previous work [Gong and Baudoin, Phys. Rev. Appl. 12, 024045 (2019)] demonstrates theoretically in two dimensions (2-D) the possibility to trap and assemble small particles compared to the wavelength with synchronized acoustical tweezers based on cylindrical acoustical vortices. However, there is no trap in the beam's propagation direction since the cylindrical acoustical vortex is progressive along their central axis, leading to the fact that particles are only pushed or pulled (not trapped) in this direction and hence are mainly limited to 2-D operations. In this work, 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 (similar to the 2-D synchronized cylindrical vortices) and axially (extra to the 2-D case) and we determine the maximum assembly speed by balancing the critical radiation force and the Stokes’ drag force. These theoretical results provide guidelines to design selective acoustical tweezers able to trap and assemble small particles in three dimensions.