Scaling Rules for Microrobots with Full Energetic Autonomy

There is an increasing need for wireless autonomous micro electromechanical systems (MEMS) and microrobots that can perform various functions such as sensing, diagnosis, locomotion, actuation, implantation, material removal, manipulation, and localized drug delivery. A major problem with these systems is the production, storage, and transduction of power at the micro scale. In addition, these miniature devices cannot use existing battery packs that are commonly used to power electronic devices. These MEMS and microrobots need on-board power sources that are miniaturized to their size. Together with the energy of an external source, some basic functions of microrobots can be powered simultaneously. This study seeks to develop a theoretical framework based on a chemo-electromagnetic model for use in the design of microrobots with full energetic autonomy. We first conceive a microrobot design and derive its mathematical model; the design consists of an on-board fuel generator, electrochemical device, electromagnetic device, and a locomotion mechanism. Then we present numerical simulations to show the relationship between the consumption rate of the H2 source, power density, and angular and translational velocities at low Reynolds number. We find that power density decreases approximately linearly with the diameter, while the relative velocity with respect to the body-length is approximately inversely proportional to the size, making downscaling favourable for this class of untethered devices.