Toward Sensor to Reproduce Human Sense - The Electronic Nose Artificial Olfaction Technology - page 123

Fig. 5.4 Comparison of olfactory system with the artificial olfaction system

and artificial noses. When artificial noses are used to characterize or compare
human smell performance, the signals obtained with these devices need to be
calibrated and matched to what is considered a normal perception by a human.
What's important is that the pattern of response across the sensors is separate for
different odorants. This distinguished ability allows the system to identify an
unknown odor from the pattern of sensor responses. Each sensor in the array has a
unique response profile to the spectrum of odorants under test. To identify the odor
all the sensors in the array pattern response is used. While talking about Machine
olfaction, there is a comparison of biological olfaction can be found required and
useful, in particular the human olfactory system and the respective cognitive
processes. It's shown in Fig. 5.4 .
There are significant similarity between machine olfaction system and the
''Human-nose'' constructed by Nature. Sniffing, this moves air samples which
include molecules of odors to the thin mucus layer lining the olfactory epithelium
in the upper portion of the nasal cavity. The molecules of odor interact with the
membrane bound receptor proteins of the olfactory cells. The human nose uses the
lungs to bring the odor to the epithelium layer; in the machine olfaction system
uses Bio VOC/Breath exhaled pump.
In the olfactory system, when odor molecules communicate with the different
proteins, a series of nerve impulses entitle electrical stimulus generated by the
olfactory neurons, feed into the olfactory bulb. The overall function aim is to
reduce the noise by compressing the signals and amplifying the output. In short,
the human nose has mucous, hairs, and membranes to work as filters and con-
centrators, while in the machine olfaction system an inlet sampling system that
provides sample filtration and conditioning to protect the sensors and develop
selectivity.
The human epithelium contains the olfactory epithelium, which contains mil-
lions of sensing cells, selected from different genotypes that interact with the
odorous molecules in unique ways. The machine olfaction system contains various
types of sensors that interact differently with the sample. The chemical responses
are converted in to the electronic nerve impulses by human receptors. The unique
patterns of nerve impulses are propagating by neurons through a complex network
before reaching the higher brain for interpretation. Similarly, the chemical sensors
in the machine olfaction react with the sample and produce electrical signals.