Analysis, design and experimental characterization of electrostatically actuated gas micropumps.

Abstract

This work goal is to realize a high-performance, multi-stage micropump integrated within a wireless micro gas chromatograph (muGC) for measuring airborne environment pollutants. The work described herein focuses on the development of high-fidelity mathematical and physical design models, and the testing and validation of the most promising models with large-scale and micro-scale (MEMS) pump prototypes. It is shown that an electrostatically-actuated, multistage, diaphragm micropump with active valve control provides the best expected performance for this application. A hierarchy of models is developed to characterize the various factors governing micropump performance. This includes a thermodynamic model, an idealized reduced-order model and a reduced-order model that incorporates realistic valve flow effects and accounts for fluidic load. The reduced-order models are based on fundamental fluid dynamic principles and allow predictions of flow rate and pressure rise as a function of geometric design variables, and drive signal. The reduced order models are validated in several tests. Two-stage, 20x scale pump results reveal the need to incorporate realistic valve flow effects and the output load for accurate modeling. The more realistic reduced order model is then validated using micropumps with two and four pumping stages. The reduced order model captures the micropump performance accurately, provided that separate measurements of valve pressure losses and pump geometry are used. The four-stage micropump fabricated using theoretical model guidelines from this research provides a maximum flow rate and pressure rise of 3 cm<super> 3</super>/min and 1.75 kPa/stage respectively with a power consumption of only 4 mW per stage. The four-stage micropump occupies and area of 54 mm<super> 2</super>. Each pumping cavity has a volume of 6x10<super>-6</super> m<super> 3</super>. This performance indicates that this pump design will be sufficient to meet the requirements for extended field operation of a wireless integrated muGC. During the course of these investigations, a new phenomenon referred to as microvalve pumping was discovered. A single microvalve pump occupies an area of 4 mm<super>2</super> and has been shown to produce a maximum flow rate and pressure rise of 0.48 cm<super>3</super>/min and 520 Pa respectively. The implications of this novel finding for creating even more compact and power efficient micropump designs is discussed.