|
Article Excerpt
Capacitive and resistive relative humidity (RH) sensors are presently used in varied commercial or industrial applications, such as building HVAC/ventilation control; clean rooms in the semiconductor or automotive industries; environmental chambers for testing electronics); industrial drying; process monitoring in such industries as chemicals, electronics, food/beverage, pharmaceutical, cosmetics, and pulp/paper; data loggers; farming/agriculture; computer rooms; museums/archives; meteorology; tobacco curing; animal incubators; and biomedical analysis (e.g., cell incubation).
RH sensors have also been implemented for automobile HVAC/ windshield defogging applications, and such sensors are beginning to be used in truck engine management. Indicative of the opportunities for RH sensors in truck engines, in 2003, Cummins, Inc. (Columbus, IN) began to implement capacitive RH sensors from Humirel (Toulouse, France) in Cummins production natural gas truck engines. The RH sensor reportedly allows for improved truck engine performance and fuel economy by optimizing fueling based on the moisture level of the input air.
Moreover, RH sensors (primarily resistive types) are used in volume in certain home appliances (e.g., home air conditioning, humidifier/dehumidifiers), and higher-end production printers/copiers. Currently, RH sensors are typically incorporated in transmitters, which are in turn sold by humidity sensor manufacturers or use a purchased humidity sensor element.
Issues in humidity sensor enhancement include improving the humidity sensor's selectivity (or insensitivity to certain contaminants), enhancing the sensor's ability to function effectively in corrosive atmospheres, boosting the sensor's ability to exhibit good resistance to condensing water, expanding the sensor's humidity range, and enhancing the sensor's robustness in difficult environments.
Moreover, very high-volume applications for RH sensors could emerge and proliferate in such areas as automotive, white goods (e.g., clothes dryers), and printers/copiers (e.g., ink jet printers), if the cost of the RH sensor further declines. Micromachining technology has potential to enable miniaturized RH sensors to be manufactured at very low cost in very high volumes, thereby facilitating opportunities for RH sensors in applications generating very high volumes. Highly sensitive, stable small, and easily configurable micromachined RH sensors also could offer an attractive solution for other diverse applications where humidity sensing is vital or beneficial, such as indoor/outdoor environmental monitoring, underground moisture sensing, process monitoring (during the manufacturing of, for example, chemicals or electronics products), and biomedical analysis.
Researchers at the MEMS Design and Microfabrication Lab, Department of Engineering Science, National Cheng Kung University (Tainan, Taiwan, ROC, ++886-6-2757575-63347) have developed a MEMS-based humidity sensor with an integrated temperature sensor for signal drift compensation that has demonstrated high sensitivity, linearity, and stability when sensing humidity. Using emerging MEMS technology and micromachining techniques, the team, under the direction of Associate Professor Gwo-Bin Lee, have fabricated a humidity sensor that is capable of accessing relative humidity information at the micro-scale level.
The microfabricated humidity sensor uses a mitride/silicon microstructure, suspended at a small distance above the surface of a glass substrate,...
|
