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This thesis conceptualizes the design of a planar electrode for employment in microfluidic devices to achieve dielectrophoretic focusing and separation of micro-scale entities. The planar electrode has corrugations with two such electrodes placed parallelly to form a pair and the electric field is generated between them; the presence of corrugations enhances the non-uniformity of the electric field. For purposes of 3D focusing, two pairs of electrodes are used with each pair on both sides of the microchannel. When the applied electric voltages are equal, the micro-scale entity is focused at the center of the microchannel and when the applied electric voltages are unequal, the micro-scale entity is focused at locations other than the center of the microchannel. For purposes of achieving size-based separation, four electrode pairs are used with each pair placed on one side the microchannel; the first two pairs of electrodes 3D focus the micro-scale entities next to one of the side walls while the other two pairs of electrodes subject the big micro-scale entity to negative dielectrophoresis while the small micro-scale entity experiences negligible dielectrophoresis and this pushes the big micro-scale entity inside the microchannel hence achieving separation of particles. The conceptualized microfluidic device is mathematically modelled with the model consisting of multiple governing equations; equations of motion, continuity equation, Navier-Stoke equations, and electric voltage and electric field equations make up the mathematical model. The model experiences phenomena’s such as inertia, drag, dielectrophoresis, gravity, buoyancy, and virtual mass. All equations of the model are solved numerically using Finite Difference Method. The model is validated using experimental results from literature. The model is subsequently used for evaluating the effect of operating and geometric parameters on the performance metrics of the focusing and separation device; the performa