AC Electric Field Microfluidic Control in Microsystems

The control and handling of fluids and fluid-based samples is central to the majority of applications in the areas of Micro Analysis systems and the Lab-on-a-Chip. As a result, there is a great deal of research and industrial interest in developing specific technologies for this purpose: micropumps, micromixers, microstirrers, etc. One widely used technology in these systems is electrokinetics, the use of electric fields for the manipulation and control of fluids and particles. In DC Electrokinetic systems, high voltages (typically ~1kV) are required for controlled manipulation and separation. The use of AC electric fields presents a range of different potential applications as well as the potential for better integration into microsystems. AC Electrokinetic devices for the handling of fluid required significantly lower voltages (~10V) and therefore a four order of magnitude reduction in power requirements. This paper presents devices based on AC electroosmosis and Electrothermal Electrohydrodynamics. The first mechanism involves the interaction of the Electrical Double Layer induced on electrodes by an applied potential and the electric field generated by the same potential. The second involves the interaction of an electric field with gradients in polarisability of the fluid produced by non-uniform heating. Several different designs are presented with applications in pumping, mixing and the general area of micro AC electric field microfluidic control. A specific example is presented: the use of the technique for the local modification of streamlines and deflection of fluids is presented and applications to analysis and sensing are discussed