A Surface-Tension-Driven Propulsion and Rotation Principle for Water-Floating Mini/Micro Robots

This paper describes development and experimental verifications of a novel propulsion and rotation technique for water-floating objects. As opposed to mechanical paddling, this technique electrically controls surface tension forces acting on water-floating objects without any moving parts (so-called electrowetting-on-dielectric, EWOD). As a proof of concept, a mini water-floating boat of centimeter size is fabricated from a thin plastic foil of which outer surfaces are covered with microfabricated EWOD electrodes. Applying a voltage to the electrodes changes the symmetric configuration of surface tension on the boat, resulting in generation of propulsion and rotation in the boat. By energizing the frontal or rear EWOD electrode, linear propulsion of the boat is achieved. The maximum speed is measured to be 5 mm/s. In addition, energizing two diagonal side EWOD electrodes on the boat surface generates rotational motion at the maximum rotational speed of 20 rpm. Finally, by combining the linear propulsion and rotational actuation, a curvilinear motion with controllability is demonstrated. This novel propulsion and rotation mechanism is simple yet efficient possibly being applied to propel and maneuver water-floating mini/micro robots and boats.