  We have developed and characterized two novel micro flow sensors based on
measuring the electrical impedance of the interface between the flowing liquid
and metallic electrodes embedded on the channel walls. These flow sensors are
very simple to fabricate and use, are extremely compact and can easily be
integrated into most microfluidic systems. One of these devices is a micropore
with two tantalum/platinum electrodes on its edges; the other is a micro
channel with two tantalum /platinum electrodes placed perpendicular to the
channel on its walls. In both sensors the flow rate is measured via the
electrical impedance between the two metallic electrodes, which is the
impedance of two metal-liquid junctions in series. The dependency of the
metal-liquid junction impedance on the flow rate of the liquid has been
studied. The effects of different parameters on the sensor's outputs and its
noise behavior are investigated. Design guidelines are extracted and applied to
achieve highly sensitive micro flow sensors with low noise.
