Stealthy Movements of Micro-Swimmer Flocks

Here we unveil synergistic cooperation of micro-swimmers to form a stealth swarm that minimally disturbs the surrounding fluid. We call this mode of swarming the `concealed’ mode, which can be achieved when a group of swimmers actively collaborate to cancel out one another’s disturbing flows. We then demonstrate how such a concealed swarm can remain stealth while actively gathered around a favorite spot (e.g. a nutrient source), pointing toward a target (e.g. attacking a prey flock), or tracking a desired trajectory in space. Our findings also provide a clear road map to control and lead stealth flocks of swimming micro-robots formed through their active collaboration in minimally disturbing the host medium.