A Human-Scale Permanent Magnetic Actuation System for Wireless Millirobots*

Small-scale robots which are wirelessly actuated have a huge potential to perform biomedical tasks, such as targeted drug delivery. Traditional electromagnetic actuation systems, however, often have limited accessible volume, which restricts the controllable working space of the robots for in vivo medical applications at human scale. In this work, we report a new magnetic actuation set-up comprised of a pair of static magnets and a rotating magnet, which generates a rotational magnetic field vector on a virtual conical surface, in a large accessible volume of $50 \times 15 \times 20 \text{cm}^3$ . The magnetic field is numerically simulated and verified by experiments. A millimeter-sized, gear-shaped magnetic robot (GearBot) with sharp spikes is developed. We demonstrate its ability to crawl on biological tissue phantoms with full controllability to follow designed complicated trajectories. The permanent magnetic actuation set-up which requires neither an expensive power amplifier nor a coil cooling system has a large enough accessible volume that can in future accommodate a human patient.