Interrogation of Droplet Configuration During Electrowetting via Impedance Spectroscopy

Several parameters associated with the configuration of a microliter aqueous droplet are determined by the electrical impedance measurements conducted during electrowetting. In each case, the wetted area of a dielectric-coated electrode is first determined from the impedance data, and the known dielectric thickness and permittivity. The wetted area data is then employed in a series of identification problems. In the simplest of these, we demonstrate that the contact angle can be accurately found as a function of applied bias voltage. Thus, the Lippmann-Young (LY) curve of an electrowetting system can be determined from the impedance data alone without the use of any optical measurements. In another test, we show that the volume of a microliter droplet can be estimated from electrical impedance measurements with an error of