An Active Micromixer Based on Reverse Piezoelectricity Effect
Authors: Zhou Jie , Hashmi Ali , Xu Jie , Sekhar Praveen K. 
Published: February 2020

The objective of this research effort was to design, fabricate, and characterize a high efficient active micromixer device with an integrated piezoelectric actuator to achieve rapid and homogeneous mixing inside a microfluidic channel. Efficient and rapid fluid mixing is an important task in microfluidic applications, such as chemical and biological analysis1, DNA hybridization, drug delivery2, and so on. Microfluidic devices are an excellent platform for carrying out chemical kinetic studies and nanomaterial research. However, due to the small size of microfluidic devises, fluid flow is constrained to the low Reynolds number regime, which indicates the absence of turbulence, and hence species mixing occurs primarily as a result of molecular diffusion which requires long mixing channels and extended retention times to achieve satisfactory mixing result3. Various micromixers have been developed in recent years4. They can be classified in two categories, passive and active. The passive micromixer usually requires long channel length in order to gain the long time needed for diffusion. However, as the driving force of fluid mixing in such devices is only molecular diffusion, it requires a long time to accomplish sufficient mixing. The active micromixers usually require more complicated structure and fabrication methods. However, due to short reaction time, high throughput, and reduced reagent consumption, and effectively mixing fluids make them attractive to many application5.
In this study, we used a piezoelectric bimorph actuator (model no. T220-A4-503X. Piezo systems, INC.), which is composed of three layers (pzt-copper-pzt) and can provide very large reverse-piezoelectric deformation (on the order of micrometers). This deformation is directly used to induce fluid motion in the microchannel for mixing enhancement. To do so, the piezoelectric actuator was glued to the top wall of a shallow chamber, which is connected to the main mixing channel through a converging nozzle. The deformation of piezo (together with the soft top wall of the chamber) induces volume change of the chamber, which results in very strong in/out flow at the nozzle. This oscillatory in/out flow shows great promise in enhancing mixing in the channel.
The preliminary results show that fluid mixing was remarkably promoted by the reverse piezoelectricity effect. Further optimization was deemed necessary to understand the effect of the reverse piezoelectricity, driving frequency, the driving voltage and the flow rates on mixing performance. Overall, our experiments demonstrate that reverse piezoelectricity effect facilitates simple and an inexpensive way to rapidly and homogenously mix fluid in a microchannel.

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