This paper presents a novel technique for droplet transportation using a wettability gradient surface that is generated by EWOD (Electrowetting-on-dielectric). This technique can be achieved by applying a voltage to only two interdigitated and wedge-shaped electrodes: one coated with and the other without a dielectric SiO_2 film. Several experimental results showed that a decrease in SiO_2 thickness reduces the minimum required voltage, and that an application of square-wave voltage permits lower voltage transportation of a droplet than that of DC voltage. Also, droplet velocity depended on frequency of an applied square-wave voltage, and the velocity of a 15 μl deionized (DI) water droplet reached the maximum at 60 Hz.
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