High Temperature MEMS Sensors for High-Frequency Shear Stress and Pressure Measurements

The goal of the proposed project is to develop a robust, high-bandwidth, micromachined Moiré optical-based shear stress sensor and fiber optic lever pressure sensor in a single package with a remote photo-diode/fiber-optic array optical readout for high-temperature, unsteady high-speed flow measurement applications.  The time-accurate, continuous, direct measurement of fluctuating wall shear stress and pressure is currently not possible in high-temperature environments. The proposed shear stress sensor consists of optical gratings on the backside of a floating element and another with slightly different pitch on the top surface of the stationary support wafer to permit backside optical transduction.  The proposed microphone consists of a compliant diaphragm stretched over a cavity containing a single optical fiber that measures the diaphragm deflection via intensity modulation.  The optical transduction of the floating element motion is achieved by imaging the Moiré fringe movement via a sapphire fiber-optic array bundle capable of withstanding high temperatures.  The fibers are routed to a remote photo-diode array allowing for the electronics to be located away from the high temperatures of the measurement model and facility.  All sapphire construction of the sensors, package and optical fibers results in a high-temperature capable, miniature sensor package. BENEFIT: Results from this project will result in the commercial availability of instrumentation-grade, miniature sensors that directly measure instantaneous, fluctuating and mean wall shear stress and pressure in high temperature flows.  This will greatly extend the spatial and temporal resolution capabilities of existing devices as well as the overall accuracy of skin friction and pressure measurement technology. The ability to directly measure the magnitude and direction of mean and fluctuating wall shear stress and pressure in high-speed flows with a spatial resolution on the order of one millimeter or less, a bandwidth on the order of a several hundred kilohertz, and a resolution of 0.01% of the mean value currently does not exist.  As a result, the realization of the proposed sensor will have broad impact in terms of providing a critical measurement capability for hypersonic vehicle development.