Microscale mixing is difficult because the small channel-dimensions lead to low Reynolds number and the mixing is due to the diffusion only. This study focus on mixing in a microchannel based on AC electroosmosis by using a PIV technique. The zig-zag electrodes are attached at the bottom of the channel. In the experiment, polymer microspheres red fluorescing particles are used to measure the slip velocity and streamlines of the AC electroosmotic flow. At first, the slip velocity at bottom of the electrodes is measured. We find that when the frequency increase, the slip velocity increase too. The slip velocity of short electrode is faster than the other side. And the maximum slip velocity is about 250 micrometer/s. Then, an velocimetry method is presented now, which can give the vertical dimension from the diffraction pattern variations with the defocusing distances of small particle locations. At first, the lowest grey values of points are recorded. Then, the numerical simulation is done, in which the slip velocity is treated as a subsection function approach to the experiment result. And based on the streamline of the numerical simulation, a easy relationship between the lowest grey level of the particle’s pattern and Z coordinate is built successfully.

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