Abstract:

The interaction of AC electric field with the double layer surface charge creates uni-directional force, which in turn produce fluid flow for AC electroosmosis (ACEO). In the last decade ACEO has received increasing interest due to its important applications in micro total analysis systems and miniaturized biomedical devices. With the application of very low voltage (~1V_rms), ACEO can be utilized to control and manipulate particles and fluids at the micro/nano scale, which are very difficult to achieve with existing techniques, such as pressure driven flow.

A novel micropump is presented in this research for lab-on-a-chip applications that can be fabricated with MEMS-compatible semiconductor micro-fabrication. The proposed AC electroosmotic micropump is based on biased ACEO technique for symmetrical electrode array. Biased ACEO is realized by applying biased AC signals over electrode pairs, leaving the electrolyte floating; therefore, two electrodes have different electrical potentials relative to the electrolyte. With a biased AC signal, V_applied=V₀(1+cosωt) over the electrodes, the left electrode is always positive and more prone to Faradaic charging, while the other is always negative and subject to capacitive charging.

The main concept of getting the pumping action is to get the uni-directional flow by breaking the reflection-symmetry in the geometry or applied signal. In our research we have broken the symmetry by applying asymmetric voltage on the symmetric electrode pattern, which eventually breaks the symmetry of the pattern. The corresponding numerical simulations using the finite element software Comsol multiphysics (FEMLab) are also conducted to verify the concept. The good agreement between the simulations and the experimental data regarding the uni-directional flow is also demonstrated. Our analysis also has shown that by decreasing the micro-channel height, the higher surface-to-volume ratio can be achieved, that eventually increases the micro-pumping velocity. At the end of the paper feedback control of micropump is also presented.

Keyword: AC electroosmosis, micropump, microfluidic, symmetric electrode, microflow, micro-fabrication