IEEE Proof JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 11, NO. 6, DECEMBER 2002 1 Design, Fabrication, and Testing of an Electrohydrodynamic Ion-Drag Micropump Jeff Darabi, Member, IEEE, Mihai Rada, Michael M. Ohadi, and John Lawler Abstract—This paper presents the design, fabrication, and testing of a novel electrohydrodynamic (EHD) ion-drag mi- cropump. In order to maximize the electrical field gradients that are responsible for EHD pumping, we incorporated three-di- mensional (3-D) triangular bumps of solder as part of the EHD electrodes. To form these bumps, Niobium was sputter-deposited onto a ceramic substrate, coated with photoresist, optically ex- posed and etched using a reactive ion etcher to define the electrode pattern. The substrate was then “dipped” into a molten solder pool. Since the solder adheres only to the metallic film, bumps of solder form on the electrodes, giving the electrodes a significant 3-D character. The overall dimensions of the micropump are 19 mm 32 mm 1.05 mm. Four different designs were fabricated and tested. Static pressure tests were performed with a 3M Thermal Fluid (HFE-7100) as the working fluid and the optimum design was identified. The results with the thermal fluid were highly promising and indicated a pumping head of up to 700 Pa at an applied voltage of 300 V. The experimental results for the four different designs show that the presence of the 3-D bump structures significantly improves the pumping performance. Also, a much better pumping performance was obtained with the micropump in which the emitter had a saw-tooth shape. [816] Index Terms—Electrohydrodynamics (EHDs), ion-drag, mi- cropump, three-dimensional (3-D) electrode. I. INTRODUCTION T HE electrohydrodynamic (EHD) pumping uses the inter- action of an electric field with electric charges, dipoles or particles embedded in a dielectric fluid to move the fluid. The charges can be injected directly by sharp points or by special means such as adding a small amount of a liquid containing a high density of ions. The major driving force in ion drag pumps is the movement of ions across an imposed electric field. The electric field is established between a charged electrode called an emitter and a grounded electrode called a collector. If an electrical field is strong enough, the electrons that are normally present in the liquid from ionized molecules can be accelerated to ionize other molecules. The electrons, accelerated to a high speed, will act as ion producers. The Coulomb force that is pro- duced by an external electrical field affects all the charges in the fluid. The resulting net force that acts on the electrons and ions Manuscript received February 15, 2002; revised May 29, 2002. This work was supported by the Advanced Thermal and Environmental Concepts, Inc. (ATEC, Inc., College Park, MD) through a sub-contract for a project funded by the Office of Naval Research. Subject Editor C.-J. Kim. J. Darabi is with the Department of Mechanical Engineering, University of South Carolina, Columbia, SC, 29208 USA (e-mail: darabi@engr.sc.edu). M. Rada and M. M. Ohadi are with the University of Maryland, College Park, MD. J. Lawler is with the ATEC, Inc., College Park, MD. Publisher Item Identifier 10.1109/JMEMS.2002.805046. is the same. However, since the mass of the electron is negli- gible compared to the mass of the ion, the major impact on the fluid motion is produced by the motion of the ions [1]. The fric- tion between the moving ions and the working fluid drags the working fluid toward the collector, thus setting the fluid (both charged and uncharged species) in motion. Two of the most im- portant aspects of ion-drag pumping are the design of the elec- trodes and the existence of sharp points on the emitter elec- trodes at which charge injection occurs. The electric field can be generated with a variety of electrode configurations, including transverse mesh electrodes, needle or parallel electrodes, longi- tudinal traveling-wave electrodes and many others. The fact that dielectric liquids can be pumped by the injec- tion of ions in an applied electric field has been known for quite some time. Indeed, the theoretical and experimental investiga- tions of the EHD pump were widely pursued in early 1960’s. Stuetzer [1] and Pickard [2] were among the first who proposed and studied the ion-drag EHD pump. Later, many researchers [3]–[5] made further studies of the ion-drag EHD pump. Using a simplified model, Stuetzer [1] arrived at the following relation between pressure and electric field intensity: (1) where is the pressure within the fluid, the electric field in- tensity and the permittivity. The basic assumption in deriving the above equation was to use two plane-parallel electrodes to approximate the wire grid electrodes in practice. This means that the variation of charge density around point-shaped emitter was neglected. Stuetzer [1] derived the maximum static pressure ob- tainable from a dielectric liquid and ion drag pump with plane electrode as: (2) where is the threshold voltage below which no pressure is obtainable and is the spacing between the electrodes. Pickard [2] arrived at a slightly different relation for EHD pumping: (3) where , bounded between 0 and 1, is a coefficient which takes into account the influence of several factors, mainly the charge emission laws at the electrodes. An improved model of the EHD pumping by Crowley [6] in- troduced a basic understanding of ion-drag force from an elec- 1057-7157/02$17.00 © 2002 IEEE