An instrumentation-grade differential capacitive MEMS shear stress sensor system for wind tunnel applications

This dissertation describes the development of a differential capacitive microelectromechanical systems (MEMS) shear stress sensor, the associated packaging, and the interface electronics required for operation as an instrumentation-grade sensing system. The sensor is a floating element possessing a differential comb drive designed to meet the spatial and temporal requirements for use as a measurement tool for turbulent boundary layers. The capacitive sensing interface circuitry is an analog synchronous modulation/demodulation system that enables the system to make time-resolved measurements of both mean and dynamic wall shear stress events. The packaging of the sensor creates a hydraulically smooth surface for moderate Reynolds numbers with a small footprint to enable array design and non-intrusive installation. The calibration of the sensor is extended to include a new method in estimating the frequency response function of shear stress sensors and a new test bed to quantify the impact of varying humidity and temperature in the ambient environment.;The sensor system is demonstrated in three wind tunnel facilities against a variety of comparative measurement techniques and in many flow conditions. The final system exhibits a sensitivity of 6.5 mV/Pa, a bandwidth of 4.7 kHz, and is the first MEMS-based shear stress system to successfully demonstrate both mean and dynamic measurements in multiple wind tunnel facilities.