OctoMag: An Electromagnetic System for 5-DOF Wireless Manipulation

We demonstrate five-degree-of-freedom (5-DOF) wireless magnetic control of a fully untethered microrobot with a magnetic steering system we call OctoMag. Although only occupying a single hemisphere, this system is capable of isotropically applying forces on the order of 1–40 μN with unrestricted control of the 2 orienting DOF. These capabilities are enabled through the use of soft-magnetic-cores which provide an increase of approximately 20× that of air cores in magnetic-field strength, but comes at the cost of more complicated interactions between coils. We propose a modeling mechanism that assumes the field contributions of the individual currents superimpose linearly when using cores with large linear regions and negligible hysteresis. When designing the system, the locations and quantity of electromagnets were optimized with regards to the force generation in the worstcase direction predicted by the model. The resultant system is capable of both open and closed-loop operation over a workspace of 4 cm. OctoMag was primarily designed for the control of intraocular microrobots for delicate retinal procedures, but also has potential uses in other medical applications or micromanipulation under an optical microscope.