Capillary Force Actuation: A Mechatronic Perspective

Capillary force actuation is a new technology holding particular promise for microelectromechanical systems. Relying upon the ability of electrical fields to alter the capillary pressure in a liquid, this technology permits larger actuation forces and strokes than conventional microactuators. Herein, the physical principles of electrowetting are discussed along with the relationships between changing apparent contact angle and capillary bridge shape. Several configurations of capillary force actuators are reviewed. For the standard configuration with two electrowetting surfaces, both equilibrium and nonequilibrium models of actuator performance are discussed. Three applications are examined where capillary force actuators may offer significant benefits.