This paper investigates fundamental design, modeling, and control issues related to untethered biomedical microrobots guided inside the human body through external magnetic fields. Proposed areas of application for these microrobots include sensing, diagnosis, and surgical procedures in intraocular, cardiovascular, and inner-ear environments. A prototype microrobot and steering system are introduced. Fluid drag experiments performed on the prototype robot show that the 950 × 400 µm elliptical shape has a spherical equivalent diameter of 477 µm. Drag forces combined with saturation magnetization (5 × 10 5 A/m) of the prototype indicate that the required magnetic field gradients for application inside the vitreous humor and blood vessels are on the order of 0.7 T/m.

Primary challenges in the building of untethered submillimeter sized robots include propulsion methods, power supply, and control. We present a novel type of microrobot called MagMite that utilizes a new class of wireless resonant magnetic micro-actuator that accomplishes all three tasks. The term MagMite is derived from Magnetic Mite-a tribute to the underlying magnetic propulsion principle and the micro-scale dimensions of the robot. The device harvests magnetic energy from the environment and effectively transforms it into inertiaand impact-driven mechanical force while being fully controllable. It can be powered and controlled with oscillating fields in the kilohertz range and strengths as low as 2 mT, which is only roughly 50 times the average Earth magnetic field. These microrobotic agents with dimensions less than 300 1m 1 300 1m 1 70 1m and a total mass of 30-50 1g are capable of moving forward, backward and turning in place while reaching controllable speeds in excess of 12.5 mm s-1 or 42 times the robot's body length per second. The robots produce enough force to push micro-objects of similar sizes and can be visually servoed through a maze in a fully automated fashion. The prototype devices exhibit an overall degree of flexibility, controllability, and performance unmatched by other microrobots reported in the literature. The robustness of the MagMites leads to high experimental repeatability, which in turn enabled us to successfully compete in the RoboCup 2007 and 2009 Nanogram competitions. In this work it is demonstrated how the robots exhibit a plethora of driving behaviors, how they can operate on a host of unstructured surfaces under both dry and wet conditions, and how they can accomplish fully automated micromanipulation tasks. Various micro-objects ranging from beads to biological entities have been successfully manipulated. To the same

Power and propulsion are primary challenges in building untethered submillimeter robots. We present a class of actuators utilizing wireless resonant magnetic actuation which accomplishes both tasks with a high degree of control. The actuator harvests magnetic energy from the environment and transforms it to impact-driven mechanical force. It can be powered and controlled with oscillating fields in the kilohertz range and strengths as low as 2mT. The wireless resonant magnetic microactuator was incorporated in microrobots, which measure 300×300×70μm3, that are capable of moving forward, backward, and turning in place while reaching speeds in excess of 12.5mm∕s.

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