The Lewis Group, at Caltech, has worked out a unique approach to the idea of an electronic nose. They use arrays of simple, readily fabricated, chemically sensitive conducting polymer films.

When a polymer film is exposed to a vapor, some of the vapor partitions into the film, causing it to swell. The electronic nose detects an increase in the electrical resistance of the film, a value that can be quantified for each film.

An array of sensors that respond individually to particular vapors can produce a unique pattern for a given vapor mixture (see diagram). Pattern recognition done on the output signals from the electronic nose can classify, identify and even quantify, the odor being investigated (see detector array pattern). The researchers claim that this response is very similar to the way that our own olfactory sense produces diagnostic patters and then sends them to the brain.

The electronic nose can also be used over and over (just like your nose). The films return to their initial, unswollen state after the vapor source is removed; this reversibility has been demonstrated for tens of thousands of exposures.

The Caltech electronic nose has been demonstrated to detect odors in an ordinary room background; it can direct robotics to turn toward the source of the odor. Signals can be read in real-time or near real-time, because the swelling of the polymer begins immediately after exposure to the vapor.

For many people, the first exposure to the idea of an electronic nose was in science fiction writer Ray Bradbury's classic Fahrenheit 451. The fictional mechanical hound could also turn and move in the direction of an odor - very quickly, it turns out, and in real-time.

The mechanical hound slept but did not sleep, lived but did not live in its gently humming, gently vibrating, softly illuminated kennel back in a dark corner of the fire house...

Nights when things got dull, which was every night, the men slid down the brass poles, and set the ticking combinations of the olfactory system of the hound and let loose rats in the fire house areaway. Three seconds later the game was done, the rat caught half across the areaway, gripped in gentle paws while a four-inch hollow steel needle plunged down from the proboscis of the hound...
(Read more about Bradbury's mechanical hound)

There are plenty of commercial applications for an electronic nose; they could be used to detect problems in large-scale food production facilities, oil and natural gas exploration and help diagnose hazardous materials spills.

Use these links to get a snootful of additional olfactory electronics:

Read more details at the Lewis Group Electronic Nose research page.

(This Science Fiction in the News story used with permission of Technovelgy.com - where science meets fiction