ODOR DISCRIMINATION WITH AN ELECTRONIC NOSE

Smell is probably the least understood and exploited of the principal human senses, yet it is clearly important to both product and process control in many industries, such as foodstuffs, beverages, tobacco and perfumery. Advances in the field of integrated microelectronic devices have led to new instruments, robots, capable of vision and complex touch or taction, but not yet of smell. This paper reviews the research effort that has been carried out at Warwick University over recent years into the development of an electronic instrument that can mimic the human sense of smell. The approach that we have adopted is to construct a microprocessor-controlled system comprising an array of solid-state chemical gas sensors (with overlapping partial sensitivities to odorants) and associated signal processing and pattern recognition. This electronic system is based upon our present knowledge of the biological system. Our earliest electronic nose consisted of an array of only three to twelve tin dioxide thick-film sensors, yet it can discriminate between alcohols, beverages, tobacco blends and coffees. Current efforts are reported towards the fabrication of an integrated microsensor metal oxide array, the development of other electronic devices using polymeric materials, and the implementation of various pattern-recognition techniques, including correlation, principal-component analysis, cluster analysis and artificial neural networks. Finally, the application areas most likely to arouse widespread interest in the next decade are discussed.