Underwater propulsion using AC-electrowetting-actuated oscillating bubbles for swimming robots

This paper describes development and experimental verifications of a novel underwater propulsion technique using AC-electrowetting-actuated oscillating bubbles. To prove the concept of propulsion, an air bubble (300 ¿m dia. or 1.5 mm dia.) is installed on the tip of a metal rod covered with electrowetting dielectric layers. When an AC-electrowetting signal is applied between the metal rod and water medium, the bubble oscillates at the frequency of the applied signal and generates a steady streaming flow around the bubble. The streaming flow in turn generates a reaction force to the metal rod, resulting in propelling of the metal rod. The similar propulsion principle is applied to a centimeter-sized object. To the sidewalls of the object, a pair of microfabricated electrowetting electrodes with air bubbles is diagonally attached to generate a torque. When an electrowetting signal is transferred by wired or wirelessly to the electrodes, the object is rotated. These results experimentally prove that oscillating bubbles propel underwater objects, the size of which ranges from a few hundred microns to centimeters. Unlike the conventional propulsion, this technique does not need any moving solid parts, possibly providing a simple and efficient propulsion mechanism for robots swimming inside human body in applications of bio-surgery, bio-sensing and drug delivery.