First Local Pressure Drops Measurements in Microchannels With Integrated Micromachined Strain Gauges

The knowledge of the fundamental aspects of hydrodynamics at microscales is an exciting challenge. Some authors have published conflicting results concerning the friction and the thermal exchange coefficients, the transition to a turbulent flow regime (Qu et al. 2000, Mala and Di 1999, Papautsky et al. 1999). Some explanations, based on surface effects, have been proposed, but microeffects, if they are, are probably hidden by experimental artefacts. We aim at performing local measurements of pressure drops in monophasic microstreams. Precedent works (Baviere et al. 2003) have shown that a great care has to be taken with the intrepretation of anomalous or unexpected results, and that the metrological set up of these experiments is crucial. We have performed and tested cupro-nickel strain gauges micromachined on different sorts of silicon nitride membranes. The design of the gauges obeys an electrical Wheatstone bridge configuration. The experimental signals are in good agreement with the expected electromechanical response of the bridge. The sensitivity ranges from 50 to 100 μV/V/bar with a thermal drift below 0.011%.°C⁻¹. Such sensors have been integrated along smooth and rough silicon microchannels with hydraulic diameter of 15 μm, and no deviation from the laminar regime has been observed with such local pressure sensors. The micromachining of these devices is described and the first local pressure drops measurements performed with deionized water of low electrical resistivity are presented and discussed.