Direct measurement of instantaneous wall shear stress using micromachined floating elements

Abstract

Recent developments in microelectromechanical systems (MEMS)-based wall shear stress sensors have shown great promise towards providing the ability to make instantaneous, direct measurements of wall shear stress with both mean and fluctuating components. Significant challenges remain to increase sensor robustness and dc stability, reduce off-axis sensitivity while improving bandwidth and spatial resolution to accurately capture the full turbulent spectrum. This seminar presents the design, fabrication and characterization of both 1-D and 2-D micromachined wall shear stress sensor systems designed to be non-invasive to low-speed aerodynamic flows. The differential capacitive (MEMS) sensor is fabricated using a novel, low-cost approach to creating backside electrical contacts, providing a hydraulically smooth surface without the use of through-silicon vias. Fully-differential sensor electronics provide improved common-mode rejection, increased shear stress sensitivity, and reduced minimum detectable signal, thus increasing the dynamic range of the sensing system.