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Seoul, South Korea

Choi W.S.,Korea University | Choi W.S.,Auto Industrial Co. | Kim B.J.,University of Seoul | Kim J.S.,University of Seoul | And 2 more authors.
Sensor Letters | Year: 2014

Gas sensing properties of micro-electronic MOS gas sensor arrays were characterized for the noxious gases, carbon monoxide (CO), nitrogen oxides (NOX), ammonia (NH3) and formaldehyde (HCHO), and the sensor responses were investigated for the discrimination of gas species by using pattern recognition technique. In three binary mixed gas systems with oxidizing and reducing gases, the gas sensing behaviors and sensor responses were examined. The gas sensing behaviors to the mixed gas systems suggested that specific adsorption and selective activation of the adsorption sites might offer the priority for the adsorption of specific gas in gas mixtures. Gas sensitivity data were extracted and their patterns were recognized with PCA techniques. The PCA results showed good separation among the mixed gas systems, and it suggested that the gas mixture tests could be well classified and discriminated in the noxious gases and their mixtures. Copyright © 2014 American Scientific Publishers.

Yoo K.P.,Korea University | Hong H.P.,Korea University | Lee M.J.,Korea University | Min S.J.,LG Corp | And 4 more authors.
Measurement Science and Technology | Year: 2011

We report on the design, fabrication, and characterization of a non-dispersive infrared (NDIR) gas sensor using an integrated thermopile on a micromachined silicon nitride membrane. The NDIR sensor consists of an optical cavity with new specular reflectors around the light bulb. The multi-layer absorber showed an absorptance of over 90% at 3.3-4.9 νm. The thermopile with this absorber has an output voltage of 144.83 mV at a 5 mW incident power and a sensitivity of 30 V W-1. The sensitivity of the thermopile packaged with a Fresnel lens was 51 V W-1, approximately 1.7 times higher than that of a thermopile with only an absorber. This is due to the decrease in thermal mass and heat loss from a hot junction, and due to the increase in absorptance. Using this newly fabricated thermopile, we developed a small and sensitive NDIR gas detector module for accurate air quality monitoring systems for energy-saving buildings and automotive applications. Our novel sample cavity design is configured to uniformly emit collimated light into the entrance aperture of the cavity to enhance the sensitivity of the NDIR gas detector. © 2011 IOP Publishing Ltd.

An output specification calibrating apparatus for a capacitive pressure sensor. The output specification calibrating apparatus enables adjustment of non-linearity, offset, and gain of the capacitive pressure sensor in a software manner at the time of shipment. Accordingly, it is feasible to easily adjust output specifications of the capacitive pressure sensor and to thereby meet various needs of customers.

A technique for measuring vapor pressure and liquid level of a volatile liquid contained in a tank. An integrated measuring apparatus sequentially measures vapor pressure and differential pressure by use of a single pressure sensor and a switching valve which switches between paths for measurement of the vapor pressure and the differential pressure. In addition, the integrated measuring apparatus includes a pressure sensor configured to sequentially measure vapor pressure and total pressure or the combination of the vapor pressure and liquid pressure; and a switching valve configured to be connected to a vapor pressure tube and a liquid pressure tube and switch between connection paths with at least one input port of the pressure sensor, wherein the vapor pressure tube is connected to an upper part of the tank and the liquid pressure tube is connected to a lower part of the tank.

Choi W.-S.,Korea University | Choi W.-S.,Auto Industrial Co. | Kim B.-J.,University of Seoul | Lee H.-J.,University of Seoul | And 4 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2012

Micro electro mechanical systems (MEMS) platforms for gas sensing devices with the co-planar type micro-heaters were designed, fabricated and its effects on the In2O 3 gas sensors were investigated. Micro-heaters in MEMS gas sensor platforms were designed in the four-type heater patterns with different geometries. Electro-thermal characterizations showed that the designed platforms had highly thermal efficiency because the micro hot-plate structures were formed in the diaphragm and the thermal efficiencies were analyzed for all of 16 models and compared with each other, respectively. The designed micro-platforms were fabricated by MEMS process, and Indium oxide (In2O 3 nanoparticles were synthesized by sol-gel process and dropped on the MEMS platforms for detecting the noxious oxide gas (NO2α Fabricated micro-platforms had a very low power consumption in the fabricated 16-type models, especially, the minimum power consumption was 41 mW at the operating temperature of 250 γC. After experiments on gas sensing characteristics to NO2 gases, fabricated In2O 3 gas sensors had almost the same gas sensitivity (RSα at the operation temperature of 250 γC. It is concluded that the micro-heater geometries, pattern shapes and sizes, can be influential on the power consumption of the devices and its gas sensing characteristics. Copyright © 2012 American Scientific Publishers.

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