Dynamic pressure sensors for hypersonic flow measurements
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This Ph.D. dissertation will focus on the research and development of an acoustic pressure sensor tailored for hypersonic boundary layer flow measurements. Hypersonic boundary layer flows comprise shocks, laminar-to-turbulent transitions, and high-frequency turbulence with small (sub 1-mm) characteristic length scales. Non-invasive acoustic pressure measurements at the walls of such flows offer useful diagnostics and are desired by the hypersonic community. The desired sensor specification are as follows: operation up to 1,000-K temperature, 0.5-MHz bandwidth, and sensing elements spanning less than 1 mm. The chosen embodiment is a piezoelectric sensor employing AlN as the sensing material. Preliminary prototypes have been micromachined at the UT MRC. These sensors are comprised of diaphragms with 500-µm diameter and 2-µm thickness. The sensors have been packaged into a cylindrical form factor with 0.25-inch diameter for mounting in hypersonic test-tunnel facilities. The dissertation will focus on the rigorous performance characterization of these sensors, the exploration of an array embodiment to enable pressure gradient measurements, and sensor design and characterization at elevated temperatures.