Wireless resonant magnetic micro-actuators have been previously described as highly effective propulsion mechanisms for untethered mobile microrobots. The discussion thus far has been primarily relegated to a characterization of stationary devices and the de facto observation of their mobility. Before applications of microrobots can be more fully explored, devices are required that can operate reliably and repeatably in a host of operating environments. In this paper, we analyze the in situ performance of resonant magnetic actuators for microrobotic locomotion to better understand their durability, substrate requirements, and driving characteristics.

Primary challenges in the building of untethered sub-millimeter sized robots include power supply, propulsion methods, and control. We present a novel type of microrobot termed Magmite that utilizes a new class of wireless magnetic actuator which accomplishes all three tasks. The device harvests magnetic energy from the environment and effectively transforms it into mechanical propulsion while being fully controllable. This microrobotic agent with dimensions less than 300 mum times 300 mum times 70 mum is capable of maneuvering with 3 degrees of freedom. A specially prepared substrate allows for adjustable speeds exceeding 12.5 mm/s or 42 times the robot's body length per second (see accompanying video). It is powered by oscillating fields in the kHz range and strengths as low as 2 mT - roughly 50 times the average Earth magnetic field.

Microrobots experience physical phenomena that are difficult to model analytically and that are not completely captured with macro-scale prototypes. In this paper we present a reconfigurable robotic measurement system to characterize the magnetic and hydrodynamic properties of assembled-MEMS microrobots. The system consists of a powerful permanent magnet that is position controlled with a linear stage. The magnetic field is accurately characterized. Precision sensors are used to measure magnetic force as a function of applied field. The system is first used to validate an existing model for the magnetic force on a soft-magnetic ellipsoid. Next, the magnetic force on a soft-magnetic assembled-MEMS microrobot as a function of the applied field is measured experimentally. Finally, a vision tracking system is integrated with the setup to measure the hydrodynamic properties of the microrobot. The coefficient of viscous friction for the microrobot is obtained experimentally.

The active guidance of magnetic particles inside biological organisms for drug delivery, cell separation, and protein manipulation has been actively pursued in biomedical research for many years. Recent advances in the integration of magnetic materials in MEMS are enabling the convergence of these two technologies towards the realization of wireless magnetically guided biomedical microrobots. This paper discusses some of the fundamental design issues for a biomedical microrobot that is actively steered in body fluids using magnetic fields. The effects of miniaturization on magnetic, fluid drag, and gravity/buoyancy forces and on control stability are analyzed. The advantages of using hard magnetic materials and the state of the art in the integration of hard magnetic materials into MEMS devices are discussed. The analysis indicates that untethered microrobots capable of being navigated under external control within biological organisms including the human body is a realistic goal.

Current laparoscopic techniques for intraocular surgery require that the vitreous humor is removed and at least three cannulas are inserted through the sidewalls of the eye. This paper investigates an alternate intraocular surgical technique based on the use of wireless microrobots guided by external magnetic fields. Issues investigated include the effects of magnetic and viscous drag forces faced by magnetic microrobots in the vitreous humor and the 3D visual servoing of these microrobots using a single microscope view. A new active defocused tracking method is proposed for visually servoing the microrobot along the optical axis of the microscope. This method uses a purposely defocused view of the microrobot to unambiguously resolve depth while servoing. Experimental results demonstrating the method with a microrobot visually servoed in 3D at 60 Hz using a single microscope view are presented.