Electronic Nose 734g4o

ELECTRONIC NOSE BY

Sree sailaja Suravarapu (y5ec089) Email-id:[email protected]

ABSTRACT The term "electronic nose" was first used in a jocular sense during our early work with sensor arrays in the 1980's. An electronic nose (e-nose) is a device that identifies the specific components of an odor and analyzes its chemical makeup to identify it. Of all the five senses, olfaction uses the largest part of the brain and is an essential part of our daily lives. Our human nose is elegant, sensitive, and self-repairing, but the E-nose sensors do not fatigue or get the "flu". Further, the E-nose can be sent to detect toxic and otherwise hazardous situations that humans may wish to avoid. An electronic nose can be regarded as a modular system comprising a set of active materials which detect the odour, associated sensors which transduce the chemical quantity into electrical signals, followed by appropriate signal conditioning and processing to classify known odours or identify unknown odours. The signals generated by an array of odour sensors need to be processed in a sophisticated manner. An odor is composed of molecules, each of which has a specific size and shape. Each of these molecules has a correspondingly sized and shaped receptor in the human nose. When a specific receptor receives a molecule, it sends a signal to the brain and the brain identifies the smell associated with that particular molecule. Electronic noses based on the biological model work in a similar manner, albeit substituting sensors for the receptors, and transmitting the signal to a program for processing, rather than to the brain. Electronic noses are useful in various fields. Currently, the biggest market for electronic noses is the food industry. Environmental applications of electronic noses include analysis of fuel mixtures, detection of oil leaks, testing ground water for odors, and identification of household odors. Potential applications include identification of toxic wastes, air quality monitoring, and monitoring factory emissions. Sensors can detect toxic CO, which is odorless to humans. An electronic nose has applicability as a diagnostic tool. The tragic bombings in London on the 7 July 2005 have caused many to call for bag

searching at the ticket barriers on the Underground. This would cause huge delays, apart from finding the manpower to do it. A possible alternative is using an “electronic nose” to sniff out possible explosives so that only selected bags need to be searched by staff.

1.0 INTRODUCTION:

An electronic nose can be regarded as a

Scientists have endowed computers with

modular system comprising a set of

eyes to see, thanks to digital cameras,

active materials which detect the odour,

and ears to hear, via microphones and

associated sensors which transduce the

sophisticated recognition software. Now

chemical quantity into electrical signals,

they're taking computers further into the

followed

realm

the

conditioning and processing to classify

development of an artificial nose. The

known odours or identify unknown

term "electronic nose" was first used in a

odours. The "electronic nose" is a

jocular sense during our early work with

relatively new tool that may be used for

sensor arrays in the 1980's. As the

safety, quality, or process monitoring,

technology

accomplishing

of

the

senses

developed,

with

it

became

by

appropriate

in

a

few

signal

minutes

apparent that the animal and human

procedures that may presently require

olfactory systems operate on the same

days to complete. The two main

principle: A relatively small number of

components of an electronic nose are the

nonselective

sensing

receptors

allow

the

system

which

consists

of

discrimination of thousands of different

chemical sensors and the automated

odors. Electronic/artificial noses are

pattern recognition system. The sensing

being developed as systems for the

system can be an array of several

automated detection and classification of

different

odors, vapors, and gases. An electronic

chemical sensors), where each element

nose (e-nose) is a device that identifies

measures a different property of the

the specific components of an odor and

sensed chemical, or it can be a single

analyzes its chemical makeup to identify

sensing device (e.g., spectrometer) that

it.

produces an array of measurements for

2.0

WHAT

IS

ELECTRONIC NOSE?

AN

each

sensing

chemical,

combination.

or The

elements

it

can

quantity

(e.g.,

be

a and

complexity of the data collected by

comprising a set of active materials

sensors array can make conventional

which detect the odour, associated

chemical

an

sensors which transduce the chemical

automated fashion difficult. Gas sensors

quantity into electrical signals, followed

tend to have very broad selectivity,

by appropriate signal conditioning and

responding to many different substances.

processing to classify known odours or

This

identify unknown odours, see Figure 4

is

analysis

a

of

data

disadvantage

in

in

most

applications, but in the electronic nose, it is a definite advantage. ENose can detect an electronic change of 1 part per million. Although every sensor in an array may respond to a given chemical, these responses will usually be different. Figure 1 shows sets of responses of a typical sensor array to different pure chemicals:

FIGURE-2 ELECTRONIC NOSE SCHEME

Using variants of molecules found in biology it is possible to create 'senses' from electrical charges caused by the binding of the molecules to mimic the human nose. With this approach, the sensitivity of the device can be a

3.0

ELECTRONIC

NOSE

SCHEME:

as

available electronic nose. The receptors, which will be

An electronic nose can be regarded

thousand times better than the currently

a

modular

system

housed within an artificial membrane, remain in a closed steady state until

approached by smell molecules, when they will open and transmit an electrical

4.0 DATA PROCESSING

signal which will indicate the nature of

METHODS:

the odour

The signals generated by an array of odour sensors need to be processed in a sophisticated manner. The electronic nose

research

group

has

obtained

considerable experience in the use of various parametric and non-parametric pattern

analysis

techniques.

These

include the use of linear and non-linear techniques, such as discriminant function analysis,

cluster

analysis,

genetic

algorithms, fuzzy logic, and adaptive

FIGURE-3 CHEMICAL SENSOR

models. An odor is composed of ENose uses a collection of 16 different

molecules, each of which has a specific

polymer films. These films are specially

size and shape. Each of these molecules

designed to conduct electricity. When a

has a correspondingly sized and shaped

substance -- such as the stray molecules

receptor in the human nose. When a

from a glass of soda -- is absorbed into

specific receptor receives a molecule, it

these films, the films expand slightly,

sends a signal to the brain and the brain

and that changes how much electricity

identifies the smell associated with that

they conduct. Because each film is made

particular molecule. Electronic noses

of a different polymer, each one reacts to

based on the biological model work in a

each substance, or analyte, in a slightly

similar

different way. And, while the changes in

sensors

conductivity in a single polymer film

transmitting the signal to a program for

wouldn't be enough to identify an

processing, rather than to the brain.

analyte, the varied changes in 16 films

Electronic noses are one example of a

produce

growing

pattern.

a

distinctive,

identifiable

manner, for

biomimetics,

albeit

the

research or

substituting

receptors,

area

biomimicry,

and

called which

involves

human-made

applications

patterned on natural phenomena.

or primitive brain, and odors can elicit basic emotions like love, sadness, or fear The term, "electronic nose" or "E-nose" has come into common usage as a generic term for an array

of

chemical

gas

sensors

incorporated into an artificial olfaction device, after its introduction in the title of a landmark conference on this subject in Iceland in 1991. The term E-nose is not

pejorative.

There

are

striking

analogies between the artificial noses of man and the "Bio-nose" constructed by Figure-4 electronic nose

Nature. Figure 2 illustrates a biological

5.0 ANALOGY BETWEEN

nose and points out the important

THE BIOLOGICAL NOSE

features

of

this

"instrument".

AND E-NOSE: Of all the five senses, olfaction uses the largest part of the brain and is an essential part of our daily lives. Indeed, the appeal of most flavors is more related to the odor arising from volatiles than to the reaction of the taste buds

to dissolved

substances.

Our

olfactory system has evolved not only to

Fig-5 the "Biological Nose" (by Mother Nature)

enhance taste but also to warn us of dangerous situations. We can easily

Figure

detect just a few parts per billion of the

electronic nose. Comparing the two is

toxic gas hydrogen sulfide in sewer gas,

instructive.

an ability that can save our life. Olfaction is closely related to the limbic

3

illustrates

the

artificial

with the sample and produce electrical signals. A computer reads the unique pattern of signals, and interprets them with some form of intelligent pattern classification algorithm. From these similarities we can easily understand the nomenclature. However, there are still fundamental differences in both the Fig-6 Artificial Electronic Nose

The human nose uses the lungs to bring the odor to the epithelium layer; the electronic nose has a pump. The human nose has mucous, hairs, and membranes

instrumentation and software! The Bionose can perform tasks still out of reach for the E-nose, but the reverse is also true

to act as filters and concentrators, while

October 6, 2004: Onboard the space

the E-nose has an inlet sampling system

station, astronauts are surrounded by

that provides sample filtration and

ammonia. It flows through pipes,

conditioning to protect the sensors and

carrying heat generated inside the station

enhance

(by people and electronics) outside to

epithelium

selectivity. contains

The the

human olfactory

epithelium, which contains millions of

space. Ammonia helps keep the station habitable.

sensing cells, selected from 100-200 different genotypes that interact with the

But it's also a poison. And if it leaks, the

odorous molecules in unique ways. The

astronauts will need to know quickly.

E-nose has a variety of sensors that

Ammonia becomes dangerous at a

interact differently with the sample. The

concentration of a few parts per million

human receptors convert the chemical

(ppm). Humans, though, can't sense it

responses to electronic nerve impulses.

until it reaches about 50 ppmAnd then

The unique patterns of nerve impulses

there's fire. Before an electrical fire

are propagated by neurons through a

breaks out, increasing heat releases a

complex network before reaching the

variety of signature molecules. Humans

higher brain for interpretation. Similarly,

can't

the chemical sensors in the E-nose react

concentrations become high. Astronauts

sense

them

either

until

need better noses!That's why NASA is

Northwest

National

developing the Electronic Nose, or

exploring the technologies required to

ENose for short. It's a device that can

perform environmental restoration and

learn to recognize almost any compound

waste management in a cost effective

or combination of compounds. It can

manner.

even be trained to distinguish between

development of portable, inexpensive

Pepsi and Coke. Like a human nose, the

systems

ENose is amazingly versatile, yet it's

identification of contaminants in the

much more sensitive

field. Electronic noses fit this category.

This

Laboratory

effort

capable

includes of

is

the

real-time

Environmental applications of electronic noses include analysis of fuel mixtures, detection of oil leaks, testing ground water for odors, and identification of household odors. Potential applications

figure-7 working process

include identification of toxic wastes, air

6.0 ADVANTAGES OF E-NOSE:

quality

Our human nose is elegant, sensitive,

factory emissions. Sensors can detect

and

toxic CO, which is odorless to humans.

self-repairing,

but

the

E-nose

sensors do not fatigue or get the "flu". Further, the E-nose can be sent to detect toxic and otherwise hazardous situations that

humans may

6.1

ELECTRONIC

wish

monitoring

NOSES

FOR

MEDICINE:

avoid.

Because the sense of

NOSE

FOR

smell is an important sense to the

Enormous amounts of hazardous waste (nuclear, chemical, and mixed wastes) were generated by more than 40 years of weaponsÕ production in the U.S. Department of EnergyÕs complex.

ELECTRONIC

and

to

ENVIRONMENTAL MONITORING:

weaponsÕ

6.2

monitoring,

The

Pacific

physician,

an

electronic

nose

has

applicability as a diagnostic tool. An electronic nose can examine odors from the body (e.g., breath, wounds, body fluids,

etc.)

and

identify

possible

problems. Odors in the breath can be indicative of gastrointestinal problems, sinus problems, infections, diabetes, and

liver problems. Infected wounds and

production especially when qualitative

tissues emit distinctive odors that can be

results will do.

detected by an electronic nose. Odors coming from body fluids can indicate liver and bladder problems. A more futuristic application of electronic noses has

been

recently

proposed

for

telesurgery

6.4

ELECTRONIC

NOSE

FOR

MULTIMEDIA APPLICATIONS: Multimedia systems are widely used in consumer

electronics

environments

today, where humans can work and

6.3 ELECTRONICS NOSE FOR THE

communicate

through

multi-sensory

interfaces. Unfortunately smell detection

FOOD INDUSTRY:

and generation systems are not part of Currently, the biggest

today's multimedia systems. Hence we

market for electronic noses is the food

can use electronic nose in multimedia

industry. Applications of electronic noses

environment.

in the food industry include quality assessment

in

food

production,

inspection of food quality by odor,

6.5 ELECTRONIC NOSE USED IN DETECTION OF BOMBS:

control of food cooking processes, inspection

of

fish,

monitoring

the

fermentation process, ing if orange juice is natural, monitoring food and beverage inspection

odors, of

grading

beverage

whiskey, containers,

checking plastic wrap for containment of onion odor, and automated flavor control to name a few. In some instances electronic noses can be used to augment or replace s of human experts. In other cases, electronic noses can be used to reduce the amount of analytical chemistry that is performed in food

The tragic bombings in London on the 7 July 2005 have caused many to call for bag searching at the ticket barriers on the Underground. This would cause huge delays, apart from finding the manpower to do it. A possible

alternative

is

using

an

“electronic nose” to sniff out possible explosives so that only selected bags need to be searched by staff. The concept has been around for a long time, and was initially ridiculed. The basic idea is a device

that

identifies

the

specific

components of an odour and analyzes its

2.

chemical makeup to identify it. One

encyclopedia

mechanism would be an array of

nose.mht

E:\enose\Electrochemistry ---

Electrochemical

electronic sensors would sniff out the odours while a second mechanism would see if it could recognize the pattern.

3. http://science.nasa.gov/headlines/y2004/ 06oct_enose.htm

6.6 OTHER APPLICATIONS: 4. E:\enose\The Electronic Nose.mht Electronic nose can be used for early fire detection. E-nose offers an opportunity to develop an instrumental approach for the human analytical endpoints like odor, flavor, hazardous, contaminated, spoiled, and the like.

7.0 CONCLUSION: Humans are not well suited for repetitive or boring tasks that are better left to machines. No wonder the E-nose is sometimes referred to as a "sniffer". The E-nose has the interesting ability to address analytical problems that have been refractory to traditional analytical approaches. GOSPEL is a European network of excellence in Artificial Olfaction.

8.0 REFERENCE: 1. Electronics for u August 2006 edition.

5. E:\enose\12.mht 6. E:\enose\Artificial Noses ___ and Taste.mht