US Patent 8228657 Frequency-addressable apparatus and methods for actuation of liquids

Embodiments of the invention are directed to apparatus, methods, and applications involving the actuation of a semi-insulative working fluid by electromechanical forces based on electrowetting-on-dielectric (EWOD) and liquid dielectrophoresis (liquid DEP) mechanisms that are controlled by the frequency, but not the magnitude, of an AC voltage (i.e., ‘frequency-addressable). In the various apparatus embodiments of the invention, a single, frequency-addressable electrode pair includes at least one electrode that has a spatially-varying dielectric coating thickness and thus a spatially-varying electrode gap wherein at least a portion of which a volume of a working fluid can stably reside under no influence of an applied voltage. In an exemplary aspect, a frequency-addressable, bistable apparatus includes at least one wider gap and one narrower gap associated, respectively, with a thicker and a thinner dielectric coating thickness of the electrode(s). The working fluid resides in only one of the at least two gap regions only under the influence of capillary force. A brief burst of AC voltage at a selected high frequency or low frequency will move the liquid from one gap region to another (and back) by one of an EWOD-based and a DEP-based force. In an alternative aspect, an analog apparatus has a continuous, spatially-varying electrode gap in which the dielectric coating thickness on the electrodes varies smoothly in an inverse manner. Various applications to a display device, fiber optic coupler and attenuator, controlled liquid volume dispensers, spotting arrays, well plate apparatus, and others are presented, along with control methods.