Toward Sensor to Reproduce Human Sense - The Electronic Nose Artificial Olfaction Technology - page 116

5. matching the signal pattern with signatures of known chemical vapors and thus
identifying the chemical composition of the vapor,
6. taking some form of action based on the identification, and
7. cleaning the sensor array so that recognition process can take place again [ 3 ].

Sensing system and the automated PARC system are two main components of
an E-nose. Human nerve olfactory performs functions, very similar functions
performed by the sensor array in E-nose. So, the sensor array may be considered
the heart and most important component of the E-nose. The sensing system can be
an array of special sensing elements (e.g., gas sensors), where each element
measures a different property of the sensed odor or, the sensors respond to a
complex odor with overlapped sensitivity, which results in the sensor array pro-
ducing a distinguishing pattern. The PARC systems include the feature extraction
step, which extracts useful information from the sensor responses and the PARC
algorithm. The PARC system is completed by interfacing with the computer
central processing unit (CPU), identification library and detection software that
serve as the brain to process input data from the sensor array for successive data
analysis.
The sampling system is also important though it is listed as third necessary part
of an E-nose. The sampling system main lookout, that samples are supplied to the
sensor array in a reproducible way, and conditioned if necessary to adjust con-
centration, temperature, water vapor concentration, etc. Many sampling systems
also give automated measurement of a series of samples, though this is not a major
requirement. A sampling system should deliver a vapor sample to a sensor array in
a reproducible way. Its purpose is to reduce sample-to-sample variation that may
result from differences in humidity, temperature, concentration, etc., as well as to
preprocess the sample in any way that increases the quality of output data. Samples
often contain substances that are common to all, and, although the sensors are
dominated by them, they do not contribute to inequity. Numbers of criteria should
be accomplished by a good sensor. Main and important is the sensor should have
highest sensitivity to the target group of chemical compound(s) intended for
detection and with a threshold of detection similar to that of the human nose.
Electronic nose sensor operation involves interactions between gaseous mole-
cules and sensor-coating materials which modulate electrical current passing
through the sensor, detectable by a transducer that converts the modulation into a
recordable electronic signal [ 4 ]. Different number of electrochemical sensors (e.g.,
metal-oxide gas sensors, metal-oxide semiconductor field effect transistors, con-
ducting polymer gas sensors, acoustic wave gas sensors, quartz crystal microbal-
ance sensors, surface acoustic wave devices, field-effect gas sensors,
electrochemical gas sensors, pellistors, fiber-optic gas sensors) and many different
types of sensor-coating materials are classified according to additive doping
materials, the type and nature of the chemical interactions, the reversibility of the
chemical reactions and running temperature.
Various types of transducer devices in electronic-nose sensors are categorized
according to the nature of the physical signal they measure. Transduction