Remote Powering and Steering of Self-Propelling Microcircuits by Modulated Electric Field

We have demonstrated a new class of self-propelling particles based on miniature semiconductor diodes powered by an external uniform alternating electric field [1]. The millimeter-sized diodes floating in water rectify the voltage induced between their electrodes. The resulting particle-localized electroosmotic flux can propel them in the direction of either the cathode or the anode depending on their surface charge. These motile particles suggest rudimentary solutions to the problems facing self-propelling microdevices, including harvesting power from external sources for propulsion and potential for a range of additional functions. The next step in this direction is developing means of steering the moving microdevices. We will present and discuss a novel technique that allows simple and effective on-demand steering of the self-propelling diodes. We control remotely the direction of their locomotion by electronically modifying the duty cycle of the applied AC field. The diodes change their direction of motion when a DC component (wave asymmetry) is introduced into the AC signal. The DC component leads to electroosmotic redistribution of the counterions near the diode surface. The interaction of the dipole across the diode with the dipole across the redistributed counterions and the diode surface exerts torque on the diode, causing its rotation. Thus, the reversal of the direction of the local electroosmotic flux, caused by field asymmetry, leads to reversal of the direction of particle locomotion. When the duty cycle change is lower than the one needed to completely rotate the diodes, the diodes exhibit sideways motion. This new principle of combined AC+DC signal driven control of the direction of motion of self-propelling diodes can find applications in MEMs and micro-robotics.

[1]  S. T. Chang, V. N. Paunov, D. N. Petsev, O. D. Velev, Nat Mater, 6, 235-240 (2007).