Professor Khalil Najafi for his all-time support, encouragement and advice. If it was not for his deep understanding and patience, as well as respectful and humane attitude towards his students, going through hardships of the research would totally be impossible for me. My sincere acknowledgement goes to Dr. Rebecca Peterson, my supervisor and mentor, for all her unbelievably responsible, respectful and kind support of my research over the past years. I would also like to thank my other thesis committee members, Professor Luis Bernal, Professor Kensall Wise, Professor Edward Zellers and Professor Yogesh Gianchandani for their guidance and support. I would like to acknowledge my former and present group-mates and colleagues from Najafi Research Group and from Wireless Integrated MicroSensing and Systems (WIMS) Center, for their help, friendship and useful discussions. My special thanks goes to my colleague Karthik Kumar from Aerospace Engineering for his help and assistance in device testing and modeling. I would like to thank the staff and students of the Solid-State Electronics Laboratory (SSEL) and Luire Nanofabrication Facility (LNF) at the University of Michigan for all their help, in particular, sharing their expertise with me. I would also like to thank Professor Karl Grosh research group at Mechanical Engineering and the staff of Polytec facility at Dexter, MI, for their help with laser vibration analysis. My Ann Arbor experience remains a great chapter in my life thanks to all wonderful friends I made, or I enjoyed the company of, here. I would like to recognize and thank them all. In particular, I would like to thank Ms. Mahta Mousavi for all her support, love and encouragement over the past several months. This dissertation has been dedicated to my parents and my sister, who disserve the biggest appreciation of all. If it was not for their all-time love, sacrifice, support and encouragement, I would not be where I am now. iv TABLE OF CONTENTS DEDICATION ii ACKNOWLEDGMENTS iii LIST OF FIGURES vii

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We report the design, fabrication and testing of a new "stacked" multi-stage electrostatic gas micropump. Utilizing a stacked structure provides modularity as well as the ability to change the number of pumping stages post-fabrication to achieve the required pressure for a given application. The stacked design also eliminates the need for bidirectional movement of the pumping membrane. The new design presents a novel method to adjust the volume ratio of a given stage to achieve a uniform pressure increase across individual stages of the multi-stage system. A pressure difference of 1.1kPa and air flow rate of 85 μL/min is obtained by a 3-stage stacked micropump. An individual micropump stage is 5.5×4×0.5 mm 3 and each pumping/microvalve membrane is 2 × 2 mm 2 .

Micro pumps are required in gas chromatographs and other gas analysis systems. Thermodynamic and reduced order models reported in the literature consider only the deflection of pumping membranes which is insufficient to study the performance characteristics of more complicated multistage peristaltic pumps with multiple coupled chambers, active checkerboard valves and single or multiple electrodes for actuating the pumping membranes and valves. Specifically the volume displaced by the valves membranes can be significant compared to the volume displaced by the pumping membranes. In this paper a multiphysics model is extended to include the effect of valves as well the pump membranes deflections. The viscous losses in the flow through the valves are modeled using CFD while the structural behavior of the membrane is modeled using COMSOL in quasi-steady analyses and the results incorporated into the multiphysics unsteady reduced-order model. The model is validated by comparing computed flow-rate as a function of frequency with experimental results for a 4-stage micropump which are found to be within 7%. At a high flow rate condition the model results show that for a 4-stage pump the deflection of the valves significantly affects the performance of the pump.

This paper introduces a new class of compact, highly scalable and efficient membrane-based gas micropumps in which both stroke and flow-control actions are realized by checkerboard microvalves. Realized based on a novel scalable and modular microfabrication technology, the micropump reported here utilizes an unwanted secondary pumping effect, valve pumping, as the main pumping principle, eliminating the need for any pumping membrane. This reduces down the entire pumping structure to a collection of active microvalves, and hence, significantly simplifies the configuration and operation of mechanical gas micropumps and minimizes their dead volume (often the Achilles heel for gas micropumps). Valve-only pumping can produce a flow rate as high as 160 µL/min using only two valve membranes and pressure accumulations of 500 Pa, for a 4-stage device, while it also improves the total device size by 50%.