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A new silicon-based monolithic pressure-flow sensor has been developed. Its operation is based on the piezoresistive effect for pressure sensing and heat transfer for flow sensing. The sensor chip has a thermal isolation structure that is made of an oxidized porous silicon membrane. This structure thermally isolates the heating element located on the membrane from the rim of the chip. The sensor, in which the chip was mounted on a wall of an acrylate plastic pipe, was designed for biomedical applications. Measurements were made at pressures of 0-300 mmHg, water flow rates of 0-7 1/min, and fluid temperatures of 25-45°C. The temperature difference between the heating element and the fluid temperature sensing element was kept at 5°C. The sensor showed a pressure sensitivity of 1.32 µV/mmHg for 1-mA current supplied, a nonlinearity of 0.5 %F.S. for pressure sensing, an accuracy of ±10 %F.S. for flow sensing, and 90-percent response time of below 100 ms for flow sensing. The sensor was applied to the simultaneous measurements of pressure and flow rate in pulsedflow experimental systems.
Date of Publication: Dec 1987