Monitoring accurate temperature and pressure profiles in harsh environments is currently in high demand for gas turbine engines and nuclear reactor simulators. The ability to measure both quantities continuously over a region, without thermal coupling, while maintaining a small design envelope is also highly desirable. High temperature electronic devices, such as MEMS (microelectromechanical systems), have provided industry with effective sensors. However, because they rely heavily on the silicon technology, their performance is limited to just above 500°C. Beyond this temperature, silicon's mechanical properties begin to break down. Researchers have shown MEMS sensors to be accurate at temperatures reaching 600°C, but higher temperature sustainability will require a more durable material selection. Beyond the material shortcoming, the high temperatures do not effectively allow MEMS sensors to be multiplexed into large arrays. In general, fiber-optic based methods have been shown to offer many advantages over electronic based sensors and are the ideal choice for high temperature regimes and distributed sensing. In this paper, a diaphragm based design is presented. The design includes, a 3.175 mm maximum outer radius coupled with the ability of distributed pressure and temperature sensing for temperatures reaching 800°C. Finite element analysis using ANSYS along with analytical verification models have been used for the design evolution. Early attempts involved a bellows based design, where low pressure testing yielded good results. However, complexity in the design's assembly motivatd us to pursue other design options. Further design progression led us to discover that a diaphragm based design would provide a simple fabrication method and good sensitivity. For this design to be realized at high temperatures, a robust bonding method must be discovered to avoid unwantd deformation due to thermal CTE mismatch.
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