This paper presents a new generation of wireless resonant magnetic microactuator (WRMMA) type microrobot, named PolyMite. A polymer is used as a spring material in the design of the PolyMite. Compared with the previous generation of such devices, the use of a polymer, i.e., SU-8, as a spring material enables the design of a stable spring system without a significant increase in stiffness. A speed of over 20 mm/s (40 body lengths per second) was measured when the PolyMite was driven in air. Micromanipulation abilities of the PolyMites in wet environments have also been demonstrated. The agents were capable of transporting microobjects such as light polystyrene beads and heavier glass beads in water. The large output force, remote actuation, and biocompatible outer surface (SU-8 and gold) make the PolyMite an exciting candidate for biomedical applications.

We present a class of Wireless Resonant Magnetic Microactuator (WRMMA) that integrates a polymer spring/body structure with electroplated ferromagnetic masses. The new devices, which we call PolyMites as they are derived from our previous MagMites, are simpler, faster and cheaper to fabricate than the MagMite. Like their predecessor, they are capable of moving on planar surfaces in dry and wet environments. Their improved biocompatibility also extends their potential for biological applications. PolyMites are 500 μm in diameter and 55 μm in height. In air they have attained a speed of 13 mm/s, approximately 26 body lengths per second. PolyMites are capable of micromanipulation on a surface, which is demonstrated by pushing and releasing micro-objects such as polystyrene beads in water.

We apply nonsmooth multibody dynamics to describe the motion of a microrobot which is driven by the wireless resonant magnetic microactuator. We first analyze the robot using a simplified analytical model, which allows us to derive characteristic and nondimensional parameters that describe its dynamics. We then perform a numerical study to analyze the nonlinearities. We predict several nonintuitive phenomena, such as switching of the direction of the velocity with changing excitation frequency, and show that both erratic and controlled motions occur under specific conditions. Our numerical results are qualitatively consistent with experimental observations and indicate that previous speculations on the motion mechanism were incorrect. The modeling method is general and readily applies to other microrobots as well.

Central to the challenge of building sub-mm robots, or microrobots, is the development of effective power storage and locomotion mechanisms. In 2007 we introduced the Wireless Resonant Magnetic Micro-actuator (WRMMA) and its application in a successful microrobotic platform, the MagMite. The term MagMite is derived from Magnetic Mite-a tribute to the underlying magnetic propulsion principle and the microscale dimensions of the robot. The device harvests magnetic energy from the environment and effectively transforms it into impact-driven mechanical force while being fully controllable. It can be powered and controlled with oscillating fields in the kHz 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 μm × 300 μm × 70 μm are capable of moving forward, backward and turning in place while reaching speeds in excess of 12.5 mm/s 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 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 them to successfully compete in the RoboCup 2007 and 2009 Nanogram competitions. In this video contribution we offer an integrated explanation of the non-intuitive MagMite actuation principle. This is achieved with the help of computer animation in direct comparison with real experimental footage. Furthermore, new recordings of the microrobots operating under dry and wet conditions while performing automated microhandling tasks are presented.

We present a dynamic model of the wireless resonant magnetic microactuator (WRMMA), which is a key component of the MagMite family of microrobots. We analyze the interbody force and integrate the nonsmooth and nonlinear equations of motion using a time-stepping integration scheme. We investigate the influence of system parameters, such as friction, the frequency of the applied force, the magnitude of the applied field, the effect of a clamping force, and the effect on velocity when phase shifting the clamping signal with respect to the magnetic signal. Our results are qualitatively consistent with experimental observations, and explain several nonintuitive phenomena. We show that the robots are highly sensitive to the phase of the clamping force, that the velocity can switch directions with changing frequency, and that both erratic and controlled motion occur under specific conditions.

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.