Theoretical and Experimental Analysis of an Electrostatically Actuated Multi-stage Micropump with Active Valves

Abstract

Micropumps are required for various applications such as gas sensing, micro cooling and biological applications. Designing these pumps requires mathematical models to determine the effect of parameters that affect their performance. Models proposed in the literature are applicable only to specific micropumps generally operated at low frequency. For high frequency operation models require experimentally evaluated parameters. Hence, they cannot be used for designing and analyzing the performance of electrostatic micropumps. The goal of the research reported in this thesis is to develop mathematical tools for the design of multi-stage vacuum micropumps operated at high frequency utilizing electrostatic actuation and active valves for flow control. Two mathematical models are developed in this work. The first is a reduced-order acoustic model used to study the effect of operating frequency, volume ratio, valve leakage, valve timing, dynamic valve timing and transient performance on a multistage vacuum micropump. Using this model the impact of dynamic valve timing and novel multi-stage designs are analyzed and optimized to achieve vacuum efficiently. The second model is a multiphysics model, which accounts for active valve pumping, membrane deflection and electrostatic actuation. Inertial and resistance length relations are proposed using computational fluid dynamics analysis for the given valve design. Static and eigen-frequency analysis is carried out using Finite Element Analysis for a stacked membrane. This model is verified using experimental and computational techniques. Measured results for a 4-stage micropump showed three resonant points that were predicted by the model with an error of 7-21%. Due to the difficulty in measuring the pressure and flow fields inside the micropump, a high fidelity CFD model which incorporates membrane motion and cavity acoustics is used to validate pressure and flow fields assumptions used in the reduced order model. Pressure and flow rate performance determined using the reduced order model compare well with high fidelity CFD results for a 3-D device that includes pump and valve membrane motions. The reduced order model suggests for the first time the dominance of valve pumping that has been experimentally observed. Based on these results, a novel micropump design is proposed that can produce high flow rate.