Characterization of a Fully-Differential Capacitive Wall Shear Stress Sensor for Low-Speed Wind Tunnels – AIAA Jan 2018

This paper describes the development and experimental characterization of a fully-differential wall shear stress sensor system designed to be non-invasive to low-speed aerodynamic flows. The differential capacitive microelectromechanical systems (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. A differential charge amplifier provides improved performance compared to both single-ended buffer and differential voltage amplifier configurations. Initial characterization of the sensor system with a differential charge amplifier yields a wall shear stress sensitivity of 196.0 mV/Pa and a minimum detectable signal of 12.8 uPa at 1 kHz, providing a dynamic range of 138 dB based on a 100 Pa maximum shear stress. Dynamic calibration also provides a pressure rejection ratio of 101.9 dB, representing a significant reduction in pressure sensitivity for the current sensor design. Stability testing of the system for mean shear stress measurement demonstrates a measurement accuracy of +/-0.032% full scale (+/-3.2 mPa) over a 60 min period.

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