Toward Sensor to Reproduce Human Sense - The Electronic Nose Artificial Olfaction Technology - page 115

So far, sensor arrays have been used only in fairly restricted applications, such as
the controlled atmosphere of quality control for beer or coffee manufacture. There
are commercially available E-noses, which are neither miniature nor low power.
Electronic noses are designed to mimic the human sense of smell by providing
an analysis of individual chemicals or chemical mixtures. They offer an efficient
way of analyzing and comparing odors. Electronic noses have yet to reach the
capability of decomposing odors into their chemical components. E-noses pri-
marily detect and discriminate between odorants they previously ''learned''.
In the majority of E-nose applications there is a set of desired properties that
tend to be common.
Rapid response—The sensors should be able to react to and recover from an
exposed odor within an acceptable time frame. This is especially important in
applications that integrate E-nose with a robotic system, such as a mobile robot
that should move around in an environment and measure odor gradient.
Low power consumption—In most realistic systems there is a limit of power,
and thus the power consumption of the sensors should be relatively low. The
headspace, containing the sensor array is likely to involve other electrical equip-
ment such as pumps and valves which often share the same power supply.
Compact size—Smaller sensor size facilitates the integration of sensors in a
variety of platforms, including portable E-noses.
High sensitivity—The sensors should exhibit a high sensitivity to different
odorants and different concentrations of the same odorant.
Reliability—Gas sensors should behave as expected particularly over long
periods of time.
Robustness—Unwanted effects, from humidity and physical motion, should not
disturb the results from the sensor readings.
Electronic noses basically try to mimic the principle components of a mam-
malian nose. The fundamental processes that must occur for a mammalian nose to
detect and identify an odor can be summarized as follows:
1. Sniffing
2. reception and binding
3. stimulus
4. transmission
5. recognition
6. action
7. cleansing
The parallel mechanisms in an E-nose would be the following:
1. drawing in some gas from the i.e. environment, sample of food etc.,
2. confer the vapor molecules to react with an array of sensors,
3. detecting signals indicating the reaction of the sensors to the vapor,
4. transmitting these signals to a neural network or some other PARC mechanism,