Open-loop electrowetting actuation with micro-stepping

Abstract

Microfluidic-driven mechanical actuation opens new possibilities for positioning and manipulating delicate small components. However, existing microfluidic actuation methods are not well-suited to positioning with high resolution. This paper reports a method for precise, open-loop control of droplet position in finite steps by varying the duty cycle of the input signal in electrowetting actuation. When wetted to a solid object, both the droplet and the solid can be actuated. Unlike conventional electrowetting actuation methods, positioning resolution in our proposed method can be much smaller than the size of the underlying electrodes without requiring closed loop feedback control system. Using a leaky dielectric coating, the electrode/electrolyte combination in our device acts as a simple diode by blocking current in one direction and conducting in the other. Each duty cycle of the applied AC square wave corresponds to a unique position on the electrode. The positionduty cycle relationship is found to be nonlinear but symmetric about the center of the electrodes. This approach provides a method for improving open-loop positioning resolution without adding more electrodes. Positioning is within 0.2 mm (< 2.5 % of the droplet diameter) of the idealized model and repeatability is < 0.07 mm (< 0.8% of the droplet diameter).

Electrowetting-on-dielectric actuation of a spatial and angular manipulation MEMS stage

“…Such a configuration would also allow angular deflection along any axis of rotation within the plane of the stage. A further expansion of this concept could build on past work in which the EWOD surface was separated into an array of isolated electrodes actuated separately to induce lateral droplet motion [19][20][21]. Operation of the stage described in the present work on such an array of electrodes could allow for lateral as well as vertical translation.…”

Liquid metal actuator driven by electrochemical manipulation of surface tension

“…Micro-conveyor systems have seen some of the most direct applications of electrically controllable and reversible forces to position small objects. 5,6 Other previously named "surface tension actuators" do not directly rely on capillary effects as the driving force and instead use them to stabilize or facilitate a non-fluidic motion. 7 Although many methods for controlling interfacial energies have been demonstrated (e.g., temperature, 8 light, 9 and electrowetting 10 ), they have typically been employed to control individual liquid droplets.…”