What is an Electronic Nose ? What is an Electronic Nose ?

A device that identifies the specific components of an odour and analyses its chemical makeup to identify it using non specific chemical sensor array.

Thus, it mimics human olfaction

The Basic Idea Behind Enose When the composition

of air changes, some physical parameters of sensors change such that each of the sensors responds differently.

The gas mixtures can be identified by the pattern of response of the sensor array

Responses to a typical sensor array to different pure

chemicals

Components of Electronic NoseSensing System

Consists of chemical sensors array . Each sensor consists of conductive polymers with adsorptive surfaces.

Pattern Recognition System An odour stimulus

generates a characteristic fingerprint from sensor array that can be recognized with neural networks

Basic terminologies

OdourAn odor is made up of molecules of specific size and shape .It is due to Volatile Compounds(VOCs) which evaporate and carried away by air.

ReceptorEach molecule has correspondingly sized and shaped receptors that act as binding sites for VOCs. These VOCs are then processed by brain and the brain identifies the smell.

Block Diagram of Enose

Working Principle of E-nose An air sample is pulled by a vacuum pump through a tube into

a small chamber housing the electronic sensor array.

A sample-handling unit exposes the sensors to the odorant, producing a transient response as the VOCs interact with the active material.

The sensor response is recorded and delivered to the Signal-processing unit.

Then a washing gas such as alcohol is applied to the array for a few seconds or a minute, so as to remove the odorant mixture from the active material.

Functional Block Diagram

Schematic Block Diagram

Human Nose

How Does a Biological Nose Work? A ROSE !

Input

Mucus (filter)

Receptor Protein (sensor)

Nerve

Circuitry & NN

Would a rose smelled by any other nose smell as sweet?

Analogy Between the Electronic Nose and the Biological Nose

Inhaling Pump

Mucus Filter

Olfactory Epithelium Sensors

Binding With Proteins Interaction

nerve impulses’ unique pattern fingerprint

pattern

Nerve Impulses Circuitry & Neural Network

Analogy between biological and electronic nose

E nose over human nose

Highly versatile, more sensitive and fastE nose sensors doesn't get flu and do not

fatigueCan be used to sense toxic materials in

hazardous conditions Can work in real time for long periodsTrained human sniffers are expensive Individual variation of humans

Introduction to Sensors A sensor is a device which can respond to some properties of the environment and transform the response into an electric signal.

The output signal is the response of the sensor when the sensitive material undergoes modification.

Types of Sensors

Enose is classified on the basis of sensors used, namely:

Conductivity Sensors

Polymer sensors

Metal Oxide sensors

Calorimetric Sensors

Optical Fiber Sensors

FET Sensors

Conductivity Sensors The sensors in the electronic nose are

polymer films which have been loaded with a conductive medium, in this case carbon black.

A baseline resistance of each film is established .

As the constituents in the air change, the films swell or contract in response to the new composition of the air and resistance changes.

Calorimetric Sensors

The sensors measure the concentration of combustibles species by detecting the temperature rise resulting from the oxidation process on a catalytic element.

Optical Fiber Sensors

These utilize glass fibers with a thin chemically active material coating on their sides or ends.

A light source at a single frequency is used to interrogate the active materials which responds with the change in color to the presence of VOCs.

The active material contains chemically active fluorescent dyes immobilized in an Organic polymer matrix. As VOCs interact with it, the polarity of the

fluorescent emission spectrum changes.

Range of applications

Environmental MonitoringDetecting Explosives and bombsIn Space ExplorationFood Industry Medical ApplicationsMultimedia ApplicationsDetects skin vapors

Limitations

Electronic nose is an emerging technology because of its wide range of applications. But it also has some limitations as sensitivity of sensors have to be increased and parameters such as temperature and pressure have to be controlled. Apart, Sensor drifts have to be taken into account.

E-nose just gives the qualitative profile of gas

mixtures but not the quantitative which is also important for environmental monitoring.

Future Scope

References

www.google.comhttp://science.nasa.gov/headlines/y2004/06oc

t_Electronic Nose.htmwww.wikipedia.comArticles from ‘Electronics from you’ magazine

database.

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