Compact, Rugged, Low-Power CO2 Sensors for Autonomous Measurement of Atmospheric CO2 Concentration

65144 Compact, rugged, lightweight, low-power and low-cost CO2 sensors are needed to accurately measure atmospheric CO2 concentrations on high-altitude-capable platforms like balloons. These sensors must measure ambient CO2 concentrations with an accuracy better than ¿1 ppm, at ambient pressures as low as 0.1 atm, and at temperatures that may fall to ¿60¿C. This project will develop a new class of Micro Electrical Mechanical System (MEMS)-based ¿sensors-on-a-chip¿ for CO2 concentration measurement. These sensors will be compact, rugged, use low power, and low cost (< $20 each), and will combine all of the pieces for non-dispersive infrared spectroscopy into one component. As optical sensors they are self-calibrating and not limited by ambient temperature or pressure. In Phase I, detection of CO2 with the MEMS component was demonstrated at a precision of +0.15% over a very wide range of operating temperatures and pressures, using a lightweight, compact, multiple reflection optical cell that allowed rapid gas transfer. Because the ultimate resolution was limited by noise in prototype electronic circuits, Phase II will improve the electronics to increase precision by a factor of five. In addition, known temperature-sensitive materials will be used to further redesign the sensor chip to increase precision by another factor of ten, giving a +0.1 ppm accuracy instrument. The prototype instrument will be field-tested and compared to existing instruments to demonstrate this precision. Commercial Applications and Other Benefits as described by the awardee: Accurate, low-cost gas sensors should have applications for environmental controls (automobiles, indoor air quality, emissions control), industrial process control (fermentation, end-point detection), and safety (carbon monoxide detectors, natural gas leaks). Existing technology does not meet all requirements at sufficiently low cost, accuracy, or lifetime.