Particle Assembly with Synchronized Acoustic Tweezers

The contactless selective manipulation of individual objects at the microscale is powerfully enabled by acoustical tweezers based on acoustical vortices [M. Baudoin et al., Sci. Adv. 5, eaav1967 (2019)]. Nevertheless, the ability to assemble multiple objects with these tweezers has not been demonstrated yet and is critical for many applications, such as tissue engineering or microrobotics. To achieve this goal, it is necessary to overcome a major difficulty: the high-intensity ring which ensures the trapping of inner particles at the core of the vortex beam is repulsive for particles located outside the trap. This prevents the assembly of multiple objects. In this paper, we show (in the Rayleigh limit and in two dimensions) that this problem can be overcome by trapping the target objects at the core of two synchronized vortices. Indeed, in this case, the destructive interference between neighboring vortices enables us to create an attractive path between the captured objects. The present work may pioneer the precise assembly and patterning of particles with multitweezers.