Zig-zag arrangement of four electrodes for ac electro-osmotic micropumps

This paper deals with the mathematical modeling of traveling-wave ac electro-osmotic micropumps with a zig-zag arrangement of microelectrodes. A mathematical model based on the Poisson-Nernst-Planck-Navier-Stokes description is used in this study within the physically relevant ranges of the model parameters. We present an extensive set of parametrical studies concerning the dependence of the net velocity on a variety of parameters. We also demonstrate limits of the validity of the commonly used Capacitor-Resistor-Capacitor model. In order to achieve high net velocities, we found that there are the optimal values of the electrode length, the shift between the top and bottom electrode arrays, and the signal frequency. Performance of the zig-zag micropumps is evaluated by the means of back-pressure loads. The suggested zig-zag design brings two main benefits: (i) it allows an easier construction of four-phase traveling-wave micropumps without the need of spatially complicated electrode connections, and (ii) the zig-zag pumps can provide higher flow rates than those with single-sided coplanar arrangements. Another robust feature of the proposed zig-zag system is that a single flow reversal is observed at the ac frequency approximately six times higher than the reciprocal resistor-capacitor time even in low-amplitude regimes.