Abstract:

An indoor air monitoring device is one of the most prominent consumer applications of an electronic nose (EN). Integral gas analysis similar to biogenic odor perception can be a versatile tool to obtain continuous information about pollutants, odors, and air compositions indicating gaseous precursors of dangers such as fires. However, an EN to be used as a common household device has to combine high sensitivity and excellent gas discrimination power with inexpensiveness, small size, and low power consumption. A special gas sensor microarray of thumbnail size has been developed at the Forschungszentrum Karlsruhe based on metal-oxide technology to meet these requirements. The microarray is produced by simply partitioning a monolithic metal-oxide layer with parallel electrode strips allowing low cost fabrication. A temperature gradient and a membrane thickness gradient (on metal-oxide layer) are responsible for differentiation between the individual sensor segments and thus for the conductivity patterns that are accordingly produced. The two membranes form the basis of gas discrimination power, reliability self checks, and online noise reduction. Model gas exposures usually show detection limits lower than 1 ppm. Successful practical tests are reported on the detection of overheated wire insulation for fire prevention as well as on air quality analysis for air conditioning purposes e.g., air quality control during a meeting.