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ELECTRONIC NOSE PRESENTATION BY: SARATHPRASAD K.V NO : 45, S7 ECE B

ELECTRONIC NOSE (E NOSE)

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ELECTRONIC NOSE P R E S E N T A T I O N B Y :

S A R A T H P R A S A D K . V

N O : 4 5 , S 7 E C E B

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Contents

Introduction

Components

Sensors

Pattern recognition

Advantages & limitations

Applications

Future & conclusion

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INTRODUCTION

• Volatile organic compounds (VOC) are basic to odours

• The detection of chemicals such as industrial gases

and chemical warfare agents is important to human health and safety and

also for industrial purposes.

• But the human nose is not sensitive to all kind of VOC’s

• It is also important to have a detection system for VOC’s which are

hazardeous to human beings.

• Until now, online communication involved only two of our senses, sense of

sight & sense of hearing. A system to transfer or for the difital

reperesenation of the odour is also a matter of concern.

• These all facts lead to the requirement of an electronic detection system for

odours which is “Electronic Nose”

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WHAT IS E NOSE ?

An electronic nose (e-nose) is a device that identifies the

specific components of an odor and analyzes its chemical

makeup to identify it.

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

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WHY E NOSE ?

E-nose can be sent to detect toxic and otherwise hazardous

situations that humans may wish to avoid.

Human olfactory system may be unstable with respect to mood

or physical condition, but E-nose are not.

Accurate decision making capabilities because of pattern

matching technology

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Biological Nose Of all the five senses, olfaction uses the largest part of the

brain and is an essential part of our daily lives. Quantifying smells are useful in gas chromatography

Human nose is very sensitive

Subject to fatigue, inconsistencies, adaptation etc.

Smelling toxic gases may involve risk

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Fig. Conduction route diagram of living being olfactory system

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The sensor’s response as electrical signals is recorded and

delivered to the signal processing unit and is processed by

using the signal processing unit, whose output is undergone a

pattern recognition and comparison process that prompts

decision making.

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SENSOR1

SENSOR2

SENSOR3

A/D

DA

TA

P

RE

PR

OC

ES

SIN

G

THE PATTERN RECOGNITION

KNOWLEDGE BASE SYSTEM

A/D

A/D

……

…… …… ……

DECISION MAKING

O

D

O

U

R

1

Array of sensors Fig. Schematic diagram of an electronic nose

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Electronic Nose Correspondence of electronic nose with biological nose

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Biological nose Electronic nose

Lungs Pump

Mucus, Hair, Membrane Inlet Sampling System

Olfactory cells Sensors

Olfactory vesicle Data pre-processing module

Olfactory centre Pattern recognition module

Nerve Impulses Electrical signal

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◦ Sample handling system ◦ Generates the headspace of sample to be analyzed

◦ Exposes the odorant to the sensors

◦ Sensing system ◦ Array of different sensors

◦ Each sensor has different sensitivity to different gases

◦ Produces a pattern characteristic of the odour

◦ Signal processing & pattern recognition

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Sensing system Using array of sensors, each sensor designed to

respond to a specific chemical

Number of unique sensors must be at least as great as the number of chemicals being monitored

Each element measures a different property of the sensed chemical

Each chemical vapor presented to the sensor array produces a signature or pattern characteristic of the vapor

11 Fig. Response of sensor array to different pure chemicals

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Sensing system Use of Artificial neural networks (ANN) along with array.

Used to analyze complex data and to recognize patterns, are showing promising results in chemical vapor recognition.

ANN combined with a sensor array Number of detectable chemicals is greater than that of

sensors

Less selective sensors can be used

Less expensive too

Electronic noses incorporating ANNs have been demonstrated in various applications.

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Electronic nose sensors 1. Conductivity Sensors (a) Metal Oxide Sensor

Oxides of tin, zinc, titanium etc. doped with platinum – Active material

Doped material deposited between two metal contacts over a resistive heating element

Operating temp.: 200°C-400°C

As VOC passes over the active material, resistance changes

Resistance changes in proportion to the concentration of the VOC.

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(b) Polymer Sensor

Active material is a conducting polymer

e.g. Polypyroles , thiophenes , indoles etc

When exposed, chemicals forms bond with polymers

Bonding may be ionic or covalent

Transfer of electrons along polymer chain is affected, i.e. conductivity changes

Operate at ambient temperature, no heater required

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Conductivity Sensors

Metal Oxide Sensor Polymer Sensor

Susceptible to poisoning by sulphur compounds present in the odorant mixture

Difficult and time consuming to electro polymerize the active material

Wide availability Susceptible to humidity & can mask the responses of VOC

Relatively low cost, hence widely used

Electronic interface is simple, suitable for portable instruments

15 Fig. Comparison between metal oxide & polymer sensors

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2. Piezoelectric Sensors (a) Quartz crystal microbalance (QCM)

Consists of a resonating disk with metal electrodes on each side connected to lead wire

Resonates at a characteristic frequency (10-30 MHz) when excited with an oscillating signal

Polymer coating serves as sensing material

Gas adsorbed at the surface of the polymer increases the mass, reduces resonance frequency

Reduction is inversely proportional to mass adsorbed by the polymer

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(b) Surface acoustic-wave (SAW)

An ac signal is applied across the input metal transducer

Fingers of this gas sensor creates an acoustic wave that "surfs" the piezoelectric substrate

When the wave reaches the metal fingers of the output transducer, ac voltage is recreated

Voltage is shifted in phase as a result of the distance travelled.

Phase shift depends on the mass & the absorption properties of the sensing polymer layer

SAW devices are less sensitive than QCMs

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Limitations:

More complex electronics are needed by these sensors than conductivity ones

Resonant frequencies can drift due to the active membrane ageing

Requires frequency detectors

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Piezoelectric Sensors

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3. MOSFET Sensors

Gate is covered by noble metal catalyst, e.g. platinum, palladium, or iridium

Charge applied to the gate leads to current flow from source to drain

VOCs sweeping over the catalyst forms products that alter the sensor's gate charge

Channel conductivity varies

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MOSFET Sensors

Advantage:

Can be made with IC fabrication processes, batch to batch variation is minimized

Disadvantage :

Reaction products should penetrate the catalytic metal layer in order to influence the charge

Hermetic seal for the chip’s electrical connections in harsh environments

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4. Optical Sensors

Glass fibre coated on its sides & ends with a thin active material containing fluorescent dyes

Pulse of light from an external source propagates along the fibre

VOCs can alter the polarity of the dyes

Dyes responds by shifting fluorescent spectrum of the light

Simple fabrication- Fluorescent dyes can easily be coupled

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Signal processing & pattern recognition Main sequential steps:

Pre-processing

Feature extraction

Classification and

Decision making

Data base of the expected odorant should be compiled

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Signal processing & pattern recognition

Pre-processing Compensates for sensor drift

Compress the transient response of the sensor array

Reduces sample to sample variations

Feature extraction Reduce the dimensionality of the measurement space

Can be more readily inspected visually

Extract information relevant for pattern recognition

Performed with linear transformations e.g. PCA & LDA

Nonlinear transforms, e.g. Sammon nonlinear maps and Kohonen self organizing maps

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Signal processing & pattern recognition

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Classification

Bayesian classifiers, Artificial Neural Network(ANN) etc are used

Trained to identify the patterns that are representative of each odour

Identify the odorant by comparing it with trained ones

Decision Making

Used for application specific knowledge

Can determine whether given belong to any one in database or not

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Electronic Nose Advantages

Detection of poisonous gas is possible

Can be done in real time for long periods

Cheaper than Trained human sniffers

Individuals vary, e-nose don’t

Digital represenation of odour is possible.

Limitations Time delay between successive tests

Insensitivity to some species

According to application, e-nose has to be changed

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Applications :

Medical diagnosis and health monitoring

• Can diagnose respiratory infections such as pneumonia

• Examine odour from the body (e.g., breath, wounds,body fluids, etc.) and

identify possible problems.

• Also being studied as a diagnostic tool for lung cancer.

Environmental applications

• 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.

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Applications :

Military and security applications

• Detection of explosives and hazardous chemicals

• To detect drug odours despite other airborne odours capable of confusing

police dogs

Space applications---e-nose and NASA

• It is a full-time, continuously operating event monitor used in the

International Space Station.

• Designed to detect air contamination from spills and leaks in the crew

habitat

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Applications :

Food Industry

• Inspection of food, beverage quality by odor,

• Inspection of fish,meat etc

• Monitoring the fermentation , identification of bacteria

• Automated flavor control etc

• Characterizing coffe beans,dates,chocolates.

• To determine trimethylamine (TMA) in milk etc etc

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In process and production departments

In In quality control laboratories for at line quality control

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Future scope :

Research is being done on IC E-Noses

Miniaturizing current Technology

Improvement in sensitivity for lower levels of organisms or smaller samples

Minimizing cost

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Future scope :

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Digital Scent Technology

• To sense, transmit & receive smell through internet

• Scent is detected and processed using E Nose

• A scent is indexed along two parameters, its chemical makeup and its place

in the scent ”spectrum” and then digitized into a small file.

• Broadcast: The digital file is sent, attached to enhanced web content.

• Smell Synthesizer: The smell synthesizer means the device which is used

to generate the smells

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Conclusion Humans are not well suited for repetitive tasks.

Electronic nose has the potential to become standard tool for smelling. Researches are still going on to make electronic nose much more compact than the present one and to make e-nose ICs.

It also initiates for a new era of representing odour as an electronic/digital data like we have done on picture and sound.

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References

[1] “An Electronic Nose for Multimedia Applications “ by Rafael Castro, Mrinal Kr. Mandal, Member IEEE, Peter Ajemba, and Mujtaba A. Istihad 0098 3063/00 $10.00 © 2003 IEEE.

[2] “Electronic noses and their applications“ by E. Keller1, 0 Approved by Pacific Northwest National Laboratory (PNNL).

[3] “Electronic Nose: Current Status and Future Trends“ by Frank Ro¨ck, Nicolae Barsan, and Udo Weimar Institute of Physical and Theoretical Chemistry, University of Tu¨bingen, Auf der Morgenstelle 15, 72076 Tu¨bingen, Germany Received August 23, 2007

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