Control of multiple microrobots with multiscale magnetic field superposition

Controlled independent manipulation of multiple objects at cellular length scales in an open challenge with potential applications in life sciences and advanced manufacturing. Magnetism has been studied as a means to perform such fine scale manipulation, but generating fields that discriminate between targets at small length scales is nontrivial. We present a system for simultaneous control of multiple magnetic microrobots with characteristic lengths on the order of 10 μνα, which is based on the superposition of magnetic fields generated at centimeter scale (global) as well as micrometer scale (local). Global fields are generated with a set of four cm-scale electromagnets, while local fields are generated by microscale wires patterned on a glass substrate. Microrobots are actuated over long distances with global fields, and controlled individually or in small groups over short lengths scales. The method relies on the nonlinear relationship between magnetic force and distance. We analyze the local magnetic fields as well as simulate systems with several micropatterned wires, and experimentally demonstrate multirobot control utilizing this global/local magnetic superposition. In addition, we outline a microfabrication technique for patterning microscale wires in two dimensions. The method lends itself to scaling in terms of number of robots and size of workspace, and is compatible with other global control schemes.