An asymmetric orifice-based active micromixer in the microfluidic chip with 3D microelectrode

The fluid mixing in microscale is central to the development of flow patterns in microfluidic chips for particles separation and biological analysis. Yet, as the size of the fluid decreases, the mixing becomes challenging to change this state of flow. In this work, a novel active micromixer for enhancing the mixing performance in the micromixer with asymmetric orifices is presented. To induce the electric-driven micromixing, an AC electric field is employed to the inserted 3D microelectrodes to produce the local electric field through the asymmetric orifices located on the opposite channel walls, which is perpendicular to the main microchannel. Then the mixing experiments were conducted in a microfluidic chip comprising microelectrode with asymmetric orifices, specifically exploiting the mixing efficiency varying with the asymmetric orifice pairs, applied electric potential and frequency of the AC electric field, and flow rate. The bending degree of the mixing interface was calculated and found increasing as a function of applied electric voltage at a given AC frequency, thus enabling effective mixing crossing the microelectrode's area. The predictions are confirmed by optical microscopy experiments and the micromixing can be significantly improved as they experience longer-exposed electrical forces. The integration of multiple asymmetric orifices leads a larger zone to increase mixing efficiency and makes it a promising method for rapid and stable fluid mixing in microscale.