Artificial Perceptual Sensors - Artificial Human Sensors: Science and Applications - page 137

(1999), to also include a generally adopted statement of perceptual-based chem-
ical sensors, we end-up with the following definition:
“a perceptual-based chemical sensor is a device which comprises an array of electronic
chemical sensors with partial specificity and an appropriate pattern recognition
system, capable of recognising simple or complex quality measures ”.
An emerging interest is shown on chemical sensors, mainly due to the
increased demands on monitoring and supervision of qualitative parameters, for
example, personal safety, security and food detection.
The extensive field of feasible applications using chemical sensors as qual-
itative indicators shows that the emerging technologies will be of interest in
developing new solutions, specifically for increasing the human perceptual ability.
6.3.1 Olfaction Sensors
The extensive field of gas sensors is providing different types of operational prin-
ciples in the sensing device. The sensing techniques used have certain advantages
related to their specific application and the choice of operation principle may then
be of importance to fit the best sensing device and provide the best possible per-
formance.
The general technique in a chemical gas sensor is based on the principle that
analyte molecules get into contact with a chemical material, which is sensitive to
the molecules. The properties of the sensing material change relatively to the pres-
ence and concentration of molecules.
A traditional architecture for analysing and comparing odours is built upon
the measurement principle that the molecules containing complex compounds of
odours will leave a characteristic fingerprint that corresponds to the measured
compounds. The operational process is often included in an airtight chamber by
controlling the measurable gas, inlets and outlets. The chamber is effectively con-
trolled by the flow of measurable gas, temperature, proper reference gas and the
cleaning process required. The sensors are strategically placed in the chamber to
receive a proper amount of gas flow and the signal response is performed on each
sensor due to the individual selectivity to each measurable gas, as illustrated pre-
viously in Fig. 5.3. The response from each individual sensor will provide a finger-
print of the measured compound. The sensor response will further be processed
to achieve a specific pattern describing the quality of the gas.
The olfaction sensor is often expressed in terms of “electronic nose” sensors.
This is often misleading due to the fact that the capability and measurement prin-
ciple is not comparable with the structure of a nose. The background of the term is
related to its capabilities and the ambitious operational principle was once to con-
sequently mimic the human biological perception. However, the main concept is
still focused on the aim to identify chemical airborne odours and different chemi-
cal mixtures. The principle is not comparable to the advanced human capability of
decomposing odours into their chemical components. In fact, the olfaction sensors,