A MICROMACHINED ELECTROHYDRODYNAMIC (EHD) PUMP

A new micromachined electrohydrodynamic (EHD) injection pump is presented. The pump mainly consists of two facing grids, which are micromachined from single-crystal silicon and bonded together anodically. Pumping and static pressure generation are achieved with different polar fluids such as ethanol, propanol, acetone or deionized water. Also, most organic solvents can be pumped. With ethanol a maximum static pressure of 2.5 kPa (32 cm pumping head) and a pumping rate of 14 ml/min at a pressure of 420 Pa have been achieved. For the realized pump the grid area measures 3 mm x 3 mm and the grid separation 350-mu-m. Pumping starts at d.c. voltages as low as 40 V, whereas 700 V are needed for maximum throughput. Pumping is also observed with an a.c. driving voltage. Transient current measurements have been performed with step voltages in order to estimate the ion mobilities and transit times. To increase the pressure several of the devices can be stacked. This opens up new applications, such as micromachined cooling systems or microhydraulic actuators. The maximum flow rate and pressure head can be varied in a wide range by adjusting the dimensions of the pump. By further reducing the grid distance, driving voltages below 100 V are expected.