Untethered micro-robots, under 1 mm in size, have the potential to access small spaces for remote manipulation or sensing. Significant challenges arise in the miniaturization of robots due to the limited scaling of on-board power and computation sources. Thus, such actuation, power and computation must be generated off-board and wirelessly transmitted to the microrobot. However, due to their simplicity, low cost and small size, micro-robots could be well suited to work in large teams. A large team of tens, hundreds or thousands of micro-robots could form nodes of a wireless sensor network inside the human body, each carry a small payload to a goal inside a microfluidic channel, or perform assembly tasks in a fast and parallel micro-factory. This work concerns the use of externally-generated magnetic fields, created by electromagnetic coils outside the workspace, to provide power and commands simultaneously to the microrobots. The flexibility of this power and control scheme leads to great potential for laboratory as well as clinical applications of micro-robots in micro-manipulation and medicine. However, a major challenge associated with magnetic actuation from external coils is that all micro-robots in the workspace receive the same control signals, as the fields cannot be focused to a point.

In this work, several methods are introduced for the remote addressing of micro-scale magnetic actuators for use in untethered locomotion and micro-fluidic applications. These results constitute the first methods developed for the control of multiple magnetic microrobots which don’t require a specially patterned operating surface, and the first method for operation in 3D. Two methods of magnetic addressing are presented:​ 1) The design of heterogeneous microrobots which all respond differently to the same input magnetic field signals. Using this method, addressable locomotion on a planar surface, and floating in a liquid 3D environment are demonstrated. We show the capabilities of a small team of heterogeneous micro-robots to perform parallel manipulation of micro-objects in a confined fluid environment. 2) Through the use of magnetic composite materials, the selective disabling of micro-robot magnetization is demonstrated. Here, the magnetization of each agent is remotely and reversibly turned on and off independently. Using this method, a subset of the available micro-robots can be active, allowing for independent motion. This concept is also extended to a microfluidics application, where each of an array of magnetically-actuated micro-pumps can be driven independently as well as to the addressable actuation of a small team of micro-scale mobile magnetic grippers. This method could be extended to any remote magnetic power and control of small or micro-scale actuator groups.

The addressing methods presented are also applied for the creation of reconfigurable modular assemblies made of tens of micro-robots, which are themselves used as building blocks. Bonding by magnetic attraction and thermally-activated adhesives for these assemblies is explored, with results indicating that arbitrary shapes could be fabricated in a serial or hybrid directed assembly fashion. Addressing methods are used to independently control each module for assembly, reconfiguration and disassembly.