Gas sensors in environmental

Metal oxide semiconductor gas sensors in environmental monitoring... 

Fine, G. R, Cavanagh, L. M., Afonja, A. and Binions, R. (2010) Metal Oxide Semi-Condnctor Gas Sensors in Environmental Monitoring. Sensors 10,5468-502. 

Eine GE, Cavanagh LM, Afonja A, Binions R (2010) Metal oxide semiconductor gas sensors in environmental monitoring. Sensors 10 5469-5502... 

Gas sensors are of importance for a variety of environmental, industrial, medical, scientific and even domestic applications. The gas may be, for example, hazardous to human health, an atmospheric pollutant, or important, in terms of its concentration, for an industrial or medical process. Apart from systems merely providing an alarm signal, it is frequently required to obtain accurate real-time measurements of the concentration of a particular target gas, often in a mixture of other gases. 

The answer lies in microsystem design and fabrication, applied to a relatively simple arrangement of gas sensors (the higher the integration the better). Combined with microelectronics, it is perfectly suited for the mass production of EN modules. Microsystems are usually produced in batches and will meet demand at low cost. Additionally, small size, low energy consumption and long-term stability can be achieved. Of course, not only consumer applications will benefit from the microsystem approach, since the improvements are also relevant to instruments used in industrial applications, medical care or in environmental monitoring. 

The model analytes, which were used to show the sensor performance of the microsystems include carbon monoxide, CO, and methane, CH4. The sensor microsystems were designed for practical applications, such as environmental monitoring, industrial safety applications or household surveillance, which implies that oxygen and water vapors are present under normal operating conditions. In the following, a brief overview of the relevant gas sensor mechanisms focused on nano crystalline tin-oxide thick-film layers will be given. 

By responding to fumes in cooking areas, car parks, laboratories and similar places, gas sensors can be used to control ventilation fans. In industrial situations the sensor can monitor concentrations of carbon monoxide, ammonia, solvent vapours, hydrocarbon gases, ozone etc., and because of the growing consciousness of environmental pollution and the safety aspects of industrial processes the applications will multiply. 

Optical flame sensors can be used for detecting the initial explosion, provided interference of environmental conditions can be reliably prevented. Pressure transducers are often used because the pressure wave travels at the speed of sound and can be detected at various angles. Vibrations and other mechanical movements can interfere pressure sensors. Therefore, efforts have to be made to minimize the influence of these interferences. The suppressant must be effective in flame quenching and compatible with product and the material of the plant. The suppressors must be designed and arranged adequately, so that the suppressant is rapidly and uniformly injected to the gas mixture in the protected enclosure. 

Sensors Key technical problems involve materials and fabrication methods for both gas and liquid sensors opportunities for utilizing advanced microelectronics and membrane technologies are suggested for applications in environmental, industrial, and clinical systems, including in vivo monitoring of drug delivery systems. 

To lead into this broad subject of what materials and technologies are suitable for exhaust-gas sensors, two main questions should be considered first what is valuable to be measured or what sensor type is needed in an exhaust gas and what are the environmental conditions ... 

Electrochemical type-III sensors have been constructed for measuring NOx, C02, S02, and many other environmentally harmful gases in very low concentration ranges [5]. In these multilayer type-III gas sensors, no direct relation between a solid electrolyte and the target gas exists without the mediation of an attached auxiliary phase. 

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