S d S i S t fSensors and Sensing Systems for Machine Olfaction – Electronic Nose and Electronic Tongue

Dr. Nabarun BhattacharyyayyC-DAC, Kolkata

nabarun bhattacharya@cdackolkata innabarun.bhattacharya@cdackolkata.in

October 29, 2009

Presentation StructureHuman OlfactionMachine OlfactionElectronic Nose

Design Details and ResultsgElectronic Tongue

Design Details and ResultsgRoadmap for Research in Machine OlfactionConclusion

Human OlfactionThe olfactory region is located in the roof of the two nasal cavities Odours are sensations that occur Odours are sensations that occur when compounds (called odorants) that are carried by inhaled air stimulate receptors plocated in the olfactory epithelium. The mucous lipid, which is prod ced in the olfactor produced in the olfactory epithelium, assists in transporting the odorant molecules.Only volatile materials that are soluble in the mucous can interact with the olfactory

t d d th receptors and produces the signals that our brain interprets as odor.

Machine Olfaction

Attempts to mimic human senses of smell and taste by electronic means are called ymachine Olfaction.Sensors are the most crucial components in a machine olfaction system.Signal conditioning, data acquisition, data, data processing and pattern recognition are the crucial modules of an olfactory sensing systemsystem.

Machine Olfaction System

Human Perception Machine Sensing

Eye: VISION

E SOUND

VISION:Camera

SOUND Mi hEar: SOUND

Skin: TACTILE

SOUND:Microphone

TOUCH: Tactile

SENSES

Nose: SMELL

Devices

SMELL: E-NoseNose: SMELL

Tongue:TASTE

SMELL: E-Nose

TASTE: E-Tongue

About Electronic Nose

Electronic Nose senses complex odours using an Array of Sensors (called “sensor array”): each tuned for

d f f il f l il dodour of a family of volatile compounds.Odour stimulus imprints a characteristic electronic pattern as fingerprint (or smell print) on sensor arraypattern as fingerprint (or smell print) on sensor array. This smell print is statistically classified and resolved with suitable pattern recognition engine as a p g gmeasurement of odour of the sample.

In short, Electronic Nose is

“A scientific, reliable, repeatable, physical, non-invasive, affordable real-time techniques for various applications

like food quality assessment, environmental polution detection, medical applications, explosive detection etc.

Basic Block Diagram

Odour Delivery Sensor Array Signal System Conditioning

Data ClassificationAcquisition

Id ifi iIdentification

Od H dli & D liOdour Handling & Delivery

Headspace Sampling

Autosampling StageAir

Mass FlowController

S1

S2 S3Solenoid Valves

Sensor Cell

MeasurementCircuit

Bubbler System

TemperatureControlledBath

SyringeNeedles

Liquid Sampleq p

SSensors

Desirable Properties of electronic nose sensorselectronic nose sensors

Selectivity : Must respond to a range of chemical species.Sensitivity : Should be sensitive to detect vapour concentration range of ppm or ppbconcentration range of ppm or ppb.Speed of Response : Response time should be in the range of secondsthe range of seconds.Reproducibility : Sensors response characteristics should be reproducible.pReversibility : Should be able to recover immediately after exposure to gas.Portability : Should be small so that less sample volume may be used.

Sensors for Electronic Nose

Conductometric or Resistive

Conductance/Resistance

MOS, CP

Capacitive Capacitance PEUT Coated Electrodes

Potentiometric EMF/Voltage MOSFETGravimetric Mass/Pizeoelec SAW / QCM

tricityCalorimetric Temperature Pellisters,

ThermopileOptical RI/Wavelength

/I t it fSurface Pl/Intensity of

RadiationPlasma Sensor

Sensors for Electronic Nose

Amperometric Current Microfuel Cells/Cells/ Polarographic Sensors

Flourescent Type

Optical intensity,

Optical fibres deposited with

florescence etc.

flourescent indicator dye.

Sensors

Conducting polymer micro-sensors - Features

Conductance is altered significantly by

sensors Features

g y yinteraction with vapour species.Sensors are fabricated by electro-polymerization in controlled mannerDifferent polymers show non-overlapping selectivity to different chemicals.Fast response time with excellent reversibility

Conducting polymer micro-sensors - Advantagessensors Advantages

Excellent reproducibilityWide selectivityHigh sensitivityHigh sensitivityWide range of applicationsSt blStableLow powerOperate at ambient temperature

Metal Oxide Sensors -FeaturesFeatures

MOS are semiconducting sensing elementsmade from a metal oxide film e g tin oxidemade from a metal oxide film, e.g., tin oxideMOS operate in the range from 300 oC to500oC500 CThe sensors require O2 to functionVolatiles undergo redox reactions at thegsensor surface, resulting in a change ofconductivity across the sensorS l ti it b difi d b d i thSelectivity can be modified by doping themetal oxide (e.g with Pd, Pt) or modifying theoperating temperature of the sensoroperating temperature of the sensor

Metal Oxide Sensors -Advantages

Longevity

AdvantagesLongevitySensitivityLow response to RHLow response to RHWide range of applicationsLarge response and good discriminating power

Bulk Acoustic Wave Sensors - FeaturesSensors - Features

Quartz crystal can be coated with a wideQuartz crystal can be coated with a widerange of different selective coating filmsOn adsorbing analytes the additional mass ofOn adsorbing analytes the additional mass ofthe film results in a change in the frequencyof oscillation of the sensorA typical sensor has an operating frequencyof about 10 MHz

Bulk Acoustic Wave Sensors Advantages

High selectivity

Sensors - Advantages

Able to measure both polar and non-polarspeciesStable over a wide temperature rangeLow power (low mW)Low sensitivity to humidityHigh stabilityGood reproducibilityWell characterised coating chemistry

Intelligent Pattern Analysis

StatisticalMethods

Quantitative Supervised MLR, PLS

Pattern Analysis Unsupervised PCA CAPattern Analysis Unsupervised PCA, CA

Supervised DFA, PCR

Biologicallyinspiredmethods

ANN Unsupervised SOM

Supervised MLP, PNN, RBF,p , , ,LVQ

Fuzzy Methods Supervised FIS, FNN, FCM

Self-supervised ART, FuzzyARTMAP

Others Self-supervised GA

Supervised NFS, Wavelets

Intelligent Pattern AnalysisAnalysis

PCA – Principal Component AnalysisPLS – Partial Least SquareMLR – Multiple Linear RegressionPCR – Principal Component RegressionPCR – Principal Component RegressionDFA – Discriminant Function AnalysisLDA – Linear Discriminant AnalysisANN – Artificial Neural NetworkSOM – Self Organizing MapGA Genetic AlgorithmGA – Genetic AlgorithmART – Adaptive Resonance TheoryRBF – Radial Basis FunctionNFS – Neuro Fuzzy System

Applications of Electronic NoseNose

Environmental monitoringo Monitoring of air, water and land.Medical Diagnostics andgHealth Monitoringo Breath Monitoringo Breath Monitoringo Eye Infectiono Medical Environmental Monitoringo Medical Environmental Monitoringo Leg Ulcers

Cultured Bacteriao Cultured Bacteria

Electronic Nose applicationsapplications

Food and Beverage Applicationso Quality and process monitoring of fruits vegetableso Quality and process monitoring of fruits, vegetables,

meat, fish, brewery, coffee etc. through electronic nosehas been reported.

A t ti d A A li tiAutomotive and Aerospace Applicationso Detection of hazardous gas within automobiles,

spacecrafts.spacecrafts.Narcotic Detection.Application in Cosmetics and Fragrancepp gIndustryDetection of ExplosivesMiscellaneous upcoming Applications.

E N f TE-Nose for Tea

Sensor Selection

MOS sensors only have been considered.Procurement of Commercially Available MOS Sensors.Procurement of major

daroma determining compounds of tea.

l lExperimental TrialsFinalization of Sensor Array

MOS Sensors ConsideredTGS 2610 Propane and TGS 2201 DieselTGS 2610 Propane and

ButaneTGS 2201 Diesel

ExhaustTGS 2611 Methane TGS 823 OrganicTGS 2611 Methane TGS 823 Organic

SolventsTGS 2442 Carbon TGS 830 HalocarbonTGS 2442, TGS 203

Carbon Monoxide

TGS 830 Halocarbon Gases

TGS 2620 Alcohol TGS 831 RefrigerantsTGS 2620, TGS 822

Alcohol, Toluene, Xylene

TGS 831 Refrigerants R-21, R-22

TGS 2600 Air TGS 825 HydrogenTGS 2600 Air Contaminants

TGS 825 Hydrogen Sulphide

TGS 2180 Water Vapor TGS 826 AmmoniaTGS 2180 Water Vapor from Food

TGS 826 Ammonia

Aroma Determinants in Tea

1 2 – Phenyl-Ethanol

•Overall aroma of tea is a complex interplay of a number of volatile

Major Aroma Determinants of Tea

1 2 – Phenyl-Ethanol

2 Benzaldehyde

number of volatile flavoury compounds (VFC).

3 ß- ionone

4 Geraniol•TRA reports more than 700 biochemical volatiles

t ib t iti l5 Linalool

6 Linalool Oxide

contribute positively or negatively to tea aroma

•Kawakami et al has 6 Linalool Oxide

7 Terpeniol

•Kawakami et. al. has identified 112 aroma compounds in Darjeeling

btea by GC - MS

Sensor Response to Individual Chemicals1

0.9

1

2-phenyl-ethanolBenzaldehyde

B-ionone

Geraniol

Sensor1-TGS 2610Sensor2-TGS 2620Sensor3-TGS 2611Sensor4-TGS 2600

0.7

0.8 Geraniol

Linalool

Linalool oxideTerpeniol

Sensor5-TGS 816Sensor6-TGS 831Sensor7-TGS 832Sensor8-TGS 823

0.5

0.6

nsor

Res

pons

e

0.3

0.4Sen

0.1

0.2

1 2 3 4 5 6 7 80

Sensor Serial Number

Sensor Response to Smell of Tea

Finalization of Sensor ArrayFi li d f i t fFinalized array of sensors consists of EIGHT Figaro sensors: TGS 816, TGS 823 TGS 831 TGS 832 TGS 2600 TGS823, TGS 831, TGS 832, TGS 2600, TGS 2610, TGS 2611 and TGS 2620

Interface Circuit Diagram

Each sesnsor is a MOSsensor made from a Vc V RL

metal oxide film, e.g.,Tin OxideVolatiles undergo redox R Lgreactions at the sensorsurface, resulting in achange of conductivity

V H

R L

g yacross the sensorEach sensor is reversible.Output of each sensor is

GND

Measurement Circuit with MOS SensorOutput of each sensor iswithin TTL range.

Measurement Circuit with MOS Sensor

Signal Conditioning

The output of the sensors is analogue voltage.The sequentialThe sequential stages,namely,buffering,amplification,filtering,conversion and compensation are accomplished innversion and compensation are accomplished in the USB card used in the system for data acquisition.No additional electronics has been used for this purpose

Data Acquisition

Circuit USB 6009 card from the National Instruments has been used.DAQ system consists of sample and hold circuit anti-aliasing and analoguehold circuit,anti aliasing and analogue to digital conversion module.Analogue to digital resolution: 14bitsAnalogue to digital resolution: 14bitsSample rate :250 Ksamples/second

Signal Pre-processing

Steps of Signal Pre-processing:

Baseline identification and manipulationpCompression

Baseline Handling

Baseline refers to sensor response in no exposure conditionFractional technique of baseline qmanipulation is used for compensation against drift and contrast enhancement.g

)0()()( ss xtx −

)0(

)0()()(

s

sss x

xtxty =

)(s

Compression TechniqueCompression is a preprocessing stage where the response of sensor array is

l d futilized as a feature vector or a fingerprint by reducing the number of ddescriptors.The maximum value vector from the sensor output data has only been considered for data analysis.

=M [ ]max8max1 .............. ii SS

Characteristic Sensors Response

2.5

3

3.5

4

4.5

(V)

PurgingRegion

SaturationRegion

0

0.5

1

1.5

2

2.5

Volta

ge (V

TransientRegion

0 100 200 300 400 500 600 700 800 900-0.5

Time (Values have no significance)

Odour Handling & DeliveryA i i iA mini air compressor is used to develop requisite airflow (5 ml.

PATTERNRECOGNITION IN

COMPUTER

q (Per sec.)Three solenoid valves are used to route the

SOLINOIDVALVE-III

SENSOR ARRAY

SUCTION BLOWER

are used to route the airflow to the sample holder and the sensor AMBIENT

AIR

SOLINOID SOLINOID

VALVE III(V3)

PURGINGAMBIENTAIR

array.A blower is used to reinforce air

ODOURMOLECULES

AIR PUMP

SOLINOIDVALVE-I

(V1)

SOLINOIDVALVE-II

(V2)

AIR

reinforce air evacuation during purging.

AIR PUMP

SAMPLEVESSEL

Illumination Based Heating

The tea sample is heated for 65 seconds

PTFE FIXTUREPTFE FIXTURECOMPUTER WITH OLFACTION

SOFTWARE

secondsTemperature of the sample reaches to 60+/

ELECTRONICINTERFACE FOR

LAMP

ELECTRONICINTERFACE FOR

LAMP

HALOGEN LAMP

FAN AGITATOR

reaches to 60+/-30C35 W miniature

SAMPLEHOLDER

RTD

halogen lamp is usedHeating improves

DC MOTOR &

INTERFACE

ANALOGUEDIGITAL DIGITALUSB INTERFACE

DC MOTOR &

INTERFACE

a g p osensitivity of the system indirectly USB DATA ACQUISITION CARDUSB DATA ACQUISITION CARD

INPUTOUTPUT OUTPUTUSB INTERFACE

A Typical Sniffing Cycle A Typical Sniffing Cycle • Illumination Heating: Catalyses aroma emanation from the teaIllumination Heating: Catalyses aroma emanation from the tea

sample

• Headspace Generation: Ensures adequate concentration of• Headspace Generation: Ensures adequate concentration of volatiles released by tea within the sample holder by blowing regulated flow of air on the sample

• Sampling: During sampling; the sensor array is exposed to a constant flow of volatiles through pipelines.

• Purging: During purging operation, sensor heads are cleared with blow of fresh air so that the sensors go back to their baseline valuesvalues

• Dormancy: The system is kept in suspended animation till the next sniffing cyclenext sniffing cycle.

A Typical Sniffing CycleILLUMINATION HEATINGILLUMINATION HEATING

TIME

HEADSPACEGENERATION TIME

N V

OL

TS

4.0

SAMPLING TIME

PURGING TIMER

RE

SP

ON

SE

I

2 0

3.0

SE

NS

OR

1.0

2.0

TIME IN SECONDS

0 40 80 120 160 200 240 280 320

TIME IN SECONDS

E-Nose Prototype Developed

Sensor array Data acquisition PCBSample container with bayonet fitting

Sensor array Data acquisition PCB

Internal Operation Of E-Internal Operation Of E-Nose…

Olfaction Software

Software features:-Programmable Sequence Control-Dynamic Fermentation Profile Display-Data Logging-Alarm AnnunciationFl ibilit t it t l t th l t t i d t i-Flexibility to permit tea planters themselves to train and customize

the system as per their requirements.

D t A l iData Analysis

About Sensor Array Output⎤⎡ 181211 bbb Sensor responses

during headspace generation

⎥⎥⎥⎥⎥⎤

⎢⎢⎢⎢⎢⎡

282221

181211

......

...

...

bbb

bbb

⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢

=181211

821

...

...

......

......

hhh

SSS

bbbA

⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢

282221

181211

......

......

...

...

SSS

SSS

Sensor responses when exposed to tea odour during sampling

⎥⎥⎥⎥

⎦⎢⎢⎢⎢

⎣ 821 ...

......

mmm SSS

Data is 8-dimensionalHeadspace Duration : 30 Seconds and Sampling Duration : 50 seconds0 di d d10 readings are scanned per second

Approximately 800 rows are there in any sniffing data matrix

Data Analysis StrategyMULTIVARIATE DATA

MATRIXMATRIX

DATA EXPLORATION DATA QUANTIFICATION

DATA CO-RELATION

PRINCIPAL COMPONENT

ANALYSIS (PCA)

AROMA SCORE CALCULATION BY 2-

NORM METHOD

AROMA SCORE CALCULATION BY

MAHALANOBISANALYSIS (PCA) NORM METHOD MAHALANOBIS DISTANCE METHOD

BACK ARTIFICIAL NEURAL PROPAGATION NETWORK

RADIAL BASIS FUNCTION

PROBALISTIC NEURAL NETWORK

Results – Different ClonesWell-defined clusters are found in PCA.100% classification accuracy observed yin BP-MLP

Results – Different flavoursPCA hibi di iPCA exhibits distinct aroma clusters for teas having different 0 1

0.15

0.2

teas having different taster scores.Neural networks

0

0.05

0.1

3.60

04%

)

Neural networks exhibit varying classification ability -0.15

-0.1

-0.05

PC

A2

( 3

Taster score 8yas follows:

BP-MLP: 81% – 85% -1 -0.5 0 0.5 1 1.5-0.25

-0.2

PCA1 (96.3448%)

Taster score 5Taster score 7

Taster score 6

RBF: 86% - 91%PNN: 91% - 94%

E-Nose for Tea FermentationOxidation process

Fermentation Process Starts as soon as Tea Leaves’ cells are broken during CTC or Rolling Process

Grassy Smell Turns into Floral Smell in this ProcessGrassy Smell Turns into Floral Smell in this Process

Fermentation duration is very crucial in determining Final Q alit of TeaFinal Quality of Tea.

E-Nose can Monitor Volatile Emission Pattern during Fermentation for automatically determining and announcing the completion of useful fermentation

Sample fermentation profiles by Colorimeter

Results of PCA

Sample fermentation profiles by E-Nose

Fermentation Aroma ProfileMahalanobis Aroma Score

2-Norm Aroma Score

1.2 5

0.40.60.8

1

2-N

orm

m

a S

core

2

3

4

hal

ano

bis

m

a S

core

00.20.4

0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120

2A

ro

0

1 Mah

Aro

Time in Minutes

Detection of Fermentation Peak

Results

Colorimeter testColorimeter test

Human evaluationHuman evaluationHuman evaluationHuman evaluation

No of Fermentation run 81

Accuracy of detection of Fermentation 95%Summary of Results:

yCompletion time by E-Nose vis-à-vis Colorimeter testAccuracy of detection of Fermentation Completion time by E-Nose vis-à-vis Human E l i

96%

Evaluation

Electronic Tongue : Definition

An An ElectronicElectronic TongueTongue is an instrument which comprises of is an instrument which comprises of electrochemical cell, sensor array and appropriate pattern electrochemical cell, sensor array and appropriate pattern

iti t bl f i i i liti t bl f i i i lrecognition system, capable of recognizing simple or recognition system, capable of recognizing simple or complex soluble noncomplex soluble non--volatile molecules which forms a taste volatile molecules which forms a taste of a sample. of a sample.

The sensor array consists of broadly tuned (nonThe sensor array consists of broadly tuned (non--specific) specific) potentiometric metal based electrode that are treated with apotentiometric metal based electrode that are treated with apotentiometric metal based electrode that are treated with a potentiometric metal based electrode that are treated with a variety of common anion of a salt in solution variety of common anion of a salt in solution –– chemical chemical materials. materials.

Cont…

The Electronic Tongue is consisting of working electrode, reference electrode and counter electrode. Basically, an electrode provides an interface by which a charge can beelectrode provides an interface by which a charge can be transferred. A potential is applied consecutively to each electrode and transient current responses are collected from l t d th h d t i iti delectrode through data acquisition card.

In voltammetric method, a voltage is applied over the working electrode and reference electrode. A current is measured between working electrode and counter electrode.electrode.

Cont……..

Working Electrode: The working electrode is an innert material h G ld Pl i Gl C b I h hsuch as Gold, Platinum, or Glassy Carbon, etc. In these case, the

working electrode serve as a surface on which the electrochemical takes place. It places where redox reaction occur. p pSurface area should very less (few mm2) to limit current flow

Reference Electrode: The reference electrode is used in measuring the working electrode potential. A reference electrode should have a constant electrochemical potential as long as no current flows through it.g

Counter electrode: The counter electrode is a conductor that completes the cell circuit. It is generally innert conductor. The current flows into the solution via the working electrode leaves the solution via the counter electrode. It does not role in the redox reactionreaction.

Supporting electrolyte: salt does not react withSupporting electrolyte: salt does not react with electrodes but has conductivity

Signal appliedSignal applied

LinearDiff i l lDifferential pulseSquare waveCyclic

Sensor of Electronic Tongue

Name of SpecificationName of electrode

Specification

Working Irridium Metal wire 99 9%Working Irridium, rhodium, platinum,

Metal wire 99.9% pure; dia- 1mm

p ,palladium, Gold

Counter Platinum do

Reference Ag/Agclg g

Set of electrode

Electrodes Pin configuration

Electronic Tongue

WateTea

Liquorr

Array of ElectrodesElectrodes

Current Status vis-à-vis Work Plan

11th Plan Project jproposed

Pilot Level Deployment

NTRF Funding

Future Scope of ResearchHybrid sensor array consisting of MOS, CP and QCMand QCMDevelopment of new sensor array sensitive and selective to tea aromaand selective to tea aromaDevelopment of more efficient algorithms f b tt l t i d l ifi tifor better clustering and classificationTechniques for drift compensationIntegration of E-Nose with E-Tongue and E-Vision systems --- ENTV Systemy y

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