Optical MEMS-based Gas Sensors

The principle goal of this research program is to enhance the gas sensors utilized in industrial and indoor air-quality (IAQ) applications. Gas sensors based on optical absorption function by measuring wavelength-dependent absorption by polyatomic, asymmetric molecules. In comparison to other gas detection technologies, IR absorption has the advantages of high sensitivity, low cross-sensitivity, long life, and resistance to contamination. Presently, IR absorption is employed in both very high-performance laboratory analyzers and in very low-performance systems that detect the presence of a single gas, such as carbon monoxide. A major distinguishing feature of laboratory analyzers is the ability to measure absorption spectra over a range of wavelengths through the use of a scanning mirror element or a multi-pixel detector array. The cost, size, and power consumption of these two technologies generally limit their use to very high-end systems. This project proposes to create compact, low-cost, and low-power IR absorption sensors by replacing bulk mechanical scanning optics with a low-cost optical MEMS element.
Gas sensors have a wide range of applications in industrial safety, homeland security, medicine, and environmental monitoring. As an example, IAQ is an important existing market for gas sensors. In a demand-controlled ventilation system, the amount of fresh airflow into a room is controlled based on measurements of the indoor air-quality. Presently, IR absorption sensors are used to monitor CO2, but these sensors cannot detect the presence of other gases or contaminants. The MEMS sensors developed in this project could be used to enhance the capability of these ventilation systems, creating the capability to measure multiple gas species and hydrocarbon contaminants. The present IAQ systems provide only energy savings, but the ability to monitor for toxic gases could significantly enhance occupant safety. The mechanical robustness and compact size of the proposed MEMS sensors make them appropriate for use in a wireless sensor network, a new application area for gas sensors. These networks, which utilize distributed sensors to collect data over a wide area, have found industrial, environmental, and military applications. The role of networked sensors in IAQ applications is presently being explored at UC Berkeley?s Center for the Built Environment. Other researchers have demonstrated wireless networks for environmental monitoring. MEMS gas sensors can add new capabilities to these networks, such as the monitoring of trace gases that play an important role in urban air pollution, including CO, NOx, CO2, and H2S.