Inertial MEMS Sensors
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In this work, novel electrostatic micro-electro-mechanical system (MEMS) sensor and sensors are introduced and demonstrated. First, a novel bifurcation-based MEMS ethanol vapor sensor is demonstrated. In contrast to traditional gas sensors that measure in analog mode (quantify) gas concentration, this sensor does not quantify the gas concentration. Rather, it detects its gas concentration in binary mode, reporting (1) for concentrations above a preset threshold and (0) for concentrations below the threshold. The sensing mechanism exploits the qualitative difference between the sensor state before and after the static pull-in bifurcation in electrostatic MEMS. The transition between these states is the bifurcation used in detection. A driving circuit with a resolution of 1 mV was used to drive the sensor at a point close to the pull-in limit to achieve maximum sensitivity. The sensor was able to detect concentrations as low as 5 ppm of ethanol vapor in dry nitrogen, equivalent to a detectable mass of 165 pg. Gas detection was verified electrically and optically through a detection circuit and a CCD camera, respectively. Second, a novel tunable MEMS magnetic field sensor is demonstrated in this work. It measures torsional vibrations excited via Lorentz force. The sensor sensitivity and dynamic range can be tuned by varying a bias voltage. Experimental demonstration shows that the sensor sensitivity can be changed from 0.436 (mm/s)/mT at 6 V bias to 0.87 (mm/s)/mT at 1 V bias. Unlike most commercial magnetic sensors, this magnetic sensor achieves a higher bandwidth (182 kHz) and a tunable sensitivity adjustable on-the-fly.