A micromachined electrohydrodynamic injection pump

A micromachined electrohydrodynamic (EHD) injection pump without movable parts is presented. Pumping and static pressure generation was achieved with polar fluids such as ethanole, propanole and acetone but most organic solvents can be pumped. This opens up new applications like micromachined cooling systems, microhydraulic systems or the EHD diagnostics of liquids. With ethanole a maximum static pressure of 2.5 kPa (32 square centimetre pumping head) and a pumping rate of 14 ml/min at a pressure of 420 Pa were achieved (1). Based on the principle of acceleration of charged particles which are injected into the fluid, the pump consists mainly of two opposed grids, which are microfabricated from single crystal silicon wafers and bonded together anodically. The two grids are identical, measuring 3 mm x 3 mm with 30 mym tickness and different hole sizes in the range of 70 mym to 140 mym. This structure is easily etched into smaller than 100 bigger than silicon using a standard K O H etcha nt and a nitride masking layer. Subsequently the grid area is metallized to prevent oxidation. In order to achieve a higher static pressure without increasing the driving voltage, several devices can be stacked. Depending on the application, the maximum flow rate can be adjusted through the grid area. Alternatively, a stripe geometry can be used, or the distance between the grids can be adjusted precisely by etching back the upper grid from the frontside