In design of electrowetting-on-dielectric（ EWOD） digital microfluidic devices

more control signals are needed as the number of electrodes increases

and the design complexity of the lead wires is also increased significantly. An asymmetric electrode design in the transport direction according to the contact line theory is proposed. When voltage is applied simultaneously to the electrodes on both sides of the droplet

the electrowetting force on both sides of the droplet is unbalanced

and the droplet is transported in a specified direction. Therefore

the new device requires only two signals to achieve long-distance and large-scale unidirectional droplet transportation. A simulation model is developed using COMSOL Multiphysics to predict the EWOD force

pressure and droplet movement

and a verification experiment is also carried out to characterize the droplet actuation. Simulation and test results show that unidirectional transportation can be stably achieved on a one-dimensional path by repeated alternations of the two drive signals.