Toward Sensor to Reproduce Human Sense - The Electronic Nose Artificial Olfaction Technology - page 124

Table 5.1 Comparison between human and artificial nose (E-nose) [ 14 ]

Human Electronic

10 million receptors, self generated 5-100 chemical sensors manually replaced

10-100 selectivity classes 5-100 selectivity patterns

Initial reduction of number of signals
(1,000-1)

''Smart'' sensor arrays can be mimic

Adaptive Perhaps possible

Saturates Persistent

Signal treatment in real time Pattern recognition hardware may do this

Identifies a large number of odors Has to be trained for each application

Cannot detect some simple molecules Can detect also simple molecules (H 2 ,H 2 O,

CO 2 …)

Detects some specific molecules Not possible in general at very low

Concentrations

Associative with sound, vision, experience
etc.

Multisensor systems possible

Can get ''infected'' Can get poisoned

A computer reads the unique pattern of signals, and interprets them with some
form of intelligent pattern classification algorithm. Table 5.1 gives comparison
between the human olfaction system and electronic olfaction system [ 14 ].
The general performance of E-noses are yet comparable to that of a human
nose, already they can detect substances that are ''odourless'' to a human such as
carbon monoxide. E-noses are also capable of better detecting varying levels of
concentrations of odors.
Electronic nose research was inspired by the mechanisms involved in human
olfaction. Our sense of smell is able to recognize and discriminate extraneous
volatile compounds of diverse molecular structure with high sensitivity and
accuracy. Mimicking the perception of odors by humans is the ultimate challenge
for machine olfaction and an extremely complex regression problem.

5.7 From Reception of Odor Substances to Perception

Sensations take place any time when a stimulus activates one of the receptors.
Perception occurs when we apply our experience to understand sensations. A detail
of sensor stimuli comes from millions of sensory receptors in eyes, ears, nose,
tongue, skin, muscles, joints, and muscles. Different receptors detect different
types of physical energy, such as light waves, mechanical energy, chemical
energy, and heat energy. Receptors transduce energy from one form into another.
Transduction is defined as the transformation of stimulus energy to the electro-
chemical energy of neural impulses. Excluding for impulses of olfaction/smell
transmitted directly to the olfactory bulbs on the underside of the cortex, impulses
from sense organs are transmitted to the thalamus before the cortex. The cerebral