Biomedical Engineering Reference
In-Depth Information
and perception. Prior to finding the number of human olfactory receptors, several
scientists tried to quantify and classify odors based on the function and type of ol-
factory receptors [
100
-
103
], but this approach has been largely suspended, as it has
been identified that the number of human olfactory receptors are at least 320 [
104
].
Standardization and classification of smell is important not only for the gen-
eral odor, but also for the malodor. Since standardization of method for measuring
malodor was begun by many countries in the 1970s, studies for standardization of
malodor have mainly depended on a sensory test using human olfaction. Up to now,
malodor is recognized by several detection methods like scentometer and olfac-
tometer, which have been widely used, but these methods do not provide the exact
information together with lots of variables, mainly due to dependence on human
olfaction. The human-like smell sensing system is useful for these reasons.
Various studies are being currently carried out also for the display of olfaction,
for example, the development of a device exuding flavor through the internet, and
the development of a method and device for smell transmission. However, these
kinds of trials have a limitation, in that the device does not deliver the exact infor-
mation of a smell because there is no criterion for a variety of smells. Standardiza-
tion of smell will be an important criterion for digitalization of emotional expres-
sion of smell, as well as for various applications of smell and flavor, and therefore,
needs to be achieved by mimicking human olfaction as closely as possible.
The bioelectronic nose may be the best device mimicking the human olfactory
system, because it utilizes the human olfactory receptors as a sensing element and
employs the olfactory signaling processes. It is expected that a method for the stan-
dardization of smell can be developed through the qualitative and quantitative mea-
surement by bioelectronic nose, and eventually, that a relationship between data
from bioelectronics nose and sensory evaluation data from human olfaction would
be established. The established standard of smell can be widely utilized in various
industries such as food, beverage, agriculture, flavor and perfume, as well as bio-
medicine and environmental monitoring.
14.2.2
Multi-channel Bioelectronic Nose
The human olfactory system has an array type recognition system, which consists
of about 390 different olfactory neuron cells. Each type of olfactory neuron cell
has one kind of its own olfactory receptor on the cell surface. The olfactory system
efficiently recognizes even a wide range of odor mixtures, as well as single kind
of odor molecule, by employing the array type recognition system. This suggests
that multiple odor compounds can be precisely identified using array type sensing
system, as in the case of the human olfactory system.
Therefore it is necessary to make an array type of sensor for identifying the
profile of a mixture, as well as for enhancing the discriminative ability of the bio-
electronic nose. The array type sensor is integrated with several different types of
sensors, the number of which depends on the type of samples to be analyzed. The
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