Direct pressure and flow rate measurement in microsystems has been problematic due to micro and nano length scales. Commercially available pressure and flow rate transducers are typically orders of magnitude larger than the channel cross sections making these sensors impractical for microchannels. A novel, non-intrusive measurement technique has proven to be adaptable for making such measurements. The technique, based upon backscattering interferometry, correlates changes in interferometric fringe morphology to fluid compressibility. Sub-Pascal pressure detection has been demonstrated using an unfocused laser beam impinging on a fluid-filled, glass capillary tube. Fringe movement and thickness change, resulting from fluid velocity changes and transverse tube deflection, have been correlated to pressure values via the Hagen-Poiseuille relationships for laminar flow.

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