Reversible Swarming of Micro Robots Controlled by Acoustic Field

In recent years, simple and effective swarm control of micro-nano robots has been widely investigated owing to their potential in performing various tasks in different environments. The swarm behavior of nanorobots controlled by acoustic field, which has the advantages of simple structure, rapid migration, and immunity from electromagnetic interference, is especially suitable for lab-on-chip systems to complete various tasks. Here we demonstrate a reversible swarm behavior for a variety of micro-nano robots on a relatively large scale (6mm). The aggregation of micro-nano robots is activated by the acoustic radiation force they experienced in the applied acoustic field. Influenced by the acoustic pressure gradient, the micro-nano robots tend to migrate towards the nearest pressure node. Reversible behavior is achieved by producing streaming within the droplet through the strong resonance of the liquid film, which takes only a few seconds to disperse the aggregated cluster. The reversible swarming of micro-nano robots can be swiftly tailored by adjusting the actuation frequency and voltage. This kind of controlled movement for micro-nano robots in large areas holds great promise in diverse applications.