The term "electronic nose" was first used in a jocular sense during our early work with sensor arrays in the 1980's. An electronic nose (e-nose) is a device that identifies the specific components of an odor and analyzes its chemical makeup to identify it. Of all the five senses, olfaction uses the largest part of the brain and is an essential part of our daily lives.
Our human nose is elegant, sensitive, and self-repairing, but the E-nose sensors do not fatigue or get the "flu". Further, the E-nose can be sent to detect toxic and otherwise hazardous situations that humans may wish to avoid. An electronic nose can be regarded as a modular system comprising a set of active materials which detect the odour, associated sensors which transduce the chemical quantity into electrical signals, followed by appropriate signal conditioning and processing to classify known odours or identify unknown odours. The signals generated by an array of odour sensors need to be processed in a sophisticated manner. An odor is composed of molecules, each of which has a specific size and shape. Each of these molecules has a correspondingly sized and shaped receptor in the human nose. When a specific receptor receives a molecule, it sends a signal to the brain and the brain identifies the smell associated with that particular molecule. Electronic noses based on the biological model work in a similar manner, albeit substituting sensors for the receptors, and transmitting the signal to a program for processing, rather than to the brain.
Electronic noses are useful in various fields. Currently, the biggest market for electronic noses is the food industry. Environmental applications of electronic noses include analysis of fuel mixtures, detection of oil leaks, testing ground water for odors, and identification of household odors. Potential applications include identification of toxic wastes, air quality monitoring, and monitoring factory emissions. Sensors can detect toxic CO, which is odorless to humans. An electronic nose has applicability as a diagnostic tool. The tragic bombings in London on the 7 July 2005 have caused many to call for bag searching at the ticket barriers on the Underground. This would cause huge delays, apart from finding the manpower to do it. A possible alternative is using an ?electronic nose? to sniff out possible explosives so that only selected bags need to be searched by staff.
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