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.