Time-Sharing Acoustic Tweezers for Parallel Manipulation of Multiple Particles

Holographic acoustic tweezers have various biomedical applications due to their ability to flexibly and rapidly synthesize acoustic fields for manipulating single or multiple particles. Existing multiparticle manipulation techniques are usually realized by precisely designing the incident wave's phase distribution to synthesize a complex and steady-state acoustic field containing multiple acoustic trapping beams. However, interference effects between multiple beams tend to produce artifacts that trap particles in unwanted positions, limiting accuracy, and the number of manipulated particles. In addition, those techniques can only holistically manipulate multiple particles, namely, lacking parallel working ability. In this study, we proposed a time-sharing acoustic tweezer method to achieve the manipulation of multiple particles by rapidly switching individual trapping beams, minimizing interference artifacts. We applied this method to a 256-element phased-array acoustic tweezer system with designed ultrasonic pulse sequences to synthesize a single focused, twin trap, and vortex beam, enabling the pseudo-parallel manipulation of multiple particles in 3-D space at a beam switching frequency of ≥10 kHz. The experiments on polydimethylsiloxane particles ranging from micrometers to millimeters in diameter demonstrated that up to 96 particles can be successfully trapped and assembled into a 2-D lattice. Different numbers of particles were also patterned into dynamic contours, such as sinusoidal vibration (ten particles) and butterfly flapping (24 particles). In addition, the trapped multiple particles can also be rotated around their respective orbits. The proposed technique improved the number of objects dynamically manipulated in a parallel manner, advancing holographic acoustic tweezers and their applications.