What is the Electronic Nose?
The electronic nose consists of two components, (1) an array of chemical sensors (usually gas sensors) and (2) a pattern-recognition algorithm. The sensor array "sniffs" the vapors from a sample and provides a set of measurements; the pattern-recognizer compares the pattern of the measurements to stored patterns for known materials. Gas sensors tend to have very broad selectivity, responding to many different substances. This is a disadvantage in most applications, but in the electronic nose, it is a definite advantage. Although every sensor in an array may respond to a given chemical, these responses will usually be different. Figure 1 shows sets of responses of a typical sensor array to different pure chemicals:

The term "electronic nose" was first used in a jocular sense during our early work with sensor arrays in the 1980's. As the technology developed, it became apparent that the animal and human olfactory systems operate on the same principle: A relatively small number of nonselective receptors allow the discrimination of thousands of different odors.

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