A BIDIRECTIONAL SILICON MICROPUMP

In this paper we present a bidirectional silicon micropump. It consist s of an electrostatically actuated diaphragm and two passive check val ves. It differs from other well-known diaphragm pumps, generally refer red to as unidirectional pumps, in the layout of the valves. We have d esigned a flap valve with a first mechanical resonance frequency betwe en 1 and 2 kHz (in the fluid environment). At low actuation frequencie s (0.1-800 Hz), the pump works in the forward mode. At higher frequenc ies (2-6 kHz) the pump operates in the reverse direction. This is due to a phase shift between the response of the valves and the pressure d ifference that drives the fluid. Investigating different pump layouts, we achieve maximum pump rates of 250 and 850 mu l min(-1) in the forw ard direction as well as 400 and 200 mu l min(-1) in the reverse direc tion. The maximum back pressure is 31000 Pa (3.1 m H2O) in the forward and 7000 Pa (0.7 m H2O) in the reverse direction.