Presentation by: Ameer Iqbal Roll No.- 10EE64R02 M.Tech. (Instrumentation)

Contentsy Introduction y Components y Sensors y Pattern recognition y Wireless electronic nose y Advantages & limitations y Applications y Future & conclusion2

Biological Nosey Detection and identification of odour y Quantifying smells are useful in gas chromatography y Human nose is very sensitive y Subject to fatigue, inconsistencies, adaptation etc. y Smelling toxic gases may involve risk

Fig. Conduction route diagram of animal olfactory system

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Electronic Nosey Instrument intended to mimic the human sense of

smell y Combines human sensitivity & instrument s objective y Consists of:y Sample handling system y Sensing system y Pattern recognition system

Fig. Schematic diagram of an electronic nose

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Electronic Nosey Correspondence of electronic nose with biological noseBiological noseLungs Mucus, Hair, Membrane Olfact ry cells Olfact ry vesicle Olfact ry centre Nerve Impulses

Electronic nosePump Inlet Sampling System Sens rs Data pre-pr cessing m dule Pattern rec gniti n m dule Electrical signal

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Componentsy Sample handling systemy Generates the headspace of sample to be analyzed y Exposes the odorant to the sensors

y Sensing systemy Array of different sensors y Each sensor has different sensitivity to different gases y Produces a pattern characteristic of the odour

Fig. Response of sensor array to different pure chemicals

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Sensing systemy Quantity & complexity of the data collected can make

analysis of data in an automated system difficult. y Using array of sensors, each sensor designed to respond to a specific chemicaly Number of unique sensors must be at least as great as

the number of chemicals being monitored y Difficult to build highly selective chemical sensors y Expensive also

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Sensing systemy Use of Artificial neural networks (ANN) y ANN combined with a sensor array y Number of detectable chemicals is greater than that of sensors y Less selective sensors can be used y Less expensive too y Electronic noses incorporating ANNs have been

demonstrated in various applications.

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Electronic nose sensorsy Conductivity Sensors

(a) Metaly y y y y

xide Sensor

xides of tin, zinc, titanium etc. doped with platinum Active material Doped material deposited between two metal contacts over a resistive heating element perating temp.: 200C-400C As V C passes over the active material, resistance changes Resistance changes in proportion to the concentration of the V C.9

Conductivity Sensors(b) Polymer Sensory Active material is a conducting polymer y e.g. Polypyroles , thiophenes , indoles etc y When exposed, chemicals forms bond with polymers y Bonding may be ionic or covalent y Transfer of electrons along polymer chain is affected, i.e.

conductivity changes y perate at ambient temperature, no heater required

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Conductivity SensorsMet l Oxide Sens rSusceptible to poisoning by sulphur compounds present in the odorant mixture Wide availability Relatively low cost, hence widely used

P lymer Sens rDifficult and time consuming to electro polymerize the active material Susceptible to humidity & can mask the responses of V C Electronic interface is simple, suitable for portable instruments

ig. Comparison between metal oxide & polymer sensors11

Piezoelectric Sensors(a) Quartz crystal microbalance (QCM)y Consists of a resonating disk with metal y y y y

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 polymer12

Piezoelectric Sensors(b) Surface acoustic-wave (SAW)y y y y y y

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 QCMs13

Piezoelectric Sensorsy Limitations: y More complex electronics are needed by these sensors than conductivity ones y Resonant frequencies can drift due to the active membrane ageing y Requires frequency detectors

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M SFET Sensorsy Gate is covered by noble metal catalyst, e.g. platinum,

palladium, or iridium y Charge applied to the gate leads to current flow from source to drain y V Cs sweeping over the catalyst forms products that alter the sensor's gate charge y Channel conductivity varies

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M SFET Sensorsy Advantage: y Can be made with IC fabrication processes, batch to batch variation is minimized y Disadvantage : y Reaction products should penetrate the catalytic metal layer in order to influence the charge y Hermetic seal for the chip s electrical connections in harsh environments

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Optical Sensorsy Glass fibre coated on its sides & ends with a y y y y

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 coupled17

Signal processing & pattern recognitiony Main sequential steps: y Pre-processing y Feature extraction y Classification and y Decision making y Data base of the expected odorant should be compiled

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Signal processing & pattern recognitiony Pre-processing y Compensates for sensor drift y Compress the transient response of the sensor array y Reduces sample to sample variations y Feature extraction y Reduce the dimensionality of the measurement spacey

Can be more readily inspected visually

y Extract information relevant for pattern recognition y Performed with linear transformations e.g. PCA & LDA y Nonlinear transforms, e.g. Sammon nonlinear maps and

Kohonen self organizing maps19

Signal processing & pattern recognitiony Classificationy Bayesian classifiers, Artificial Neural Network(ANN) etc

are used y Trained to identify the patterns that are representative of each odour y Identify the odorant by comparing it with trained ones

y Decision Making y Used for application specific knowledge y Can determine that given sample does not belong to any one in database20

Wireless Electronic Nosey Developed in 2010 y Can perform remote multipoint odour monitoring y Signal from isolated locations can be combined and

processed at a database server y Data measured are delivered via ZigBee wireless network

Fig. ZigBee node of wireless electronic nose network.

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Wireless Electronic Nose(a)Electronic Hardwarey MCU acquires gas sensor data through ADC interface &

sends the data to ZigBee wireless network y Real time clock in MCU stamps date and time of the transmitted data

Fig. Block diagram of wireless electronics nose.22

Wireless Electronic Nosey Sensors were designed to be particularly sensitive to

different gases y Temp. & humidity sensors for environmental conditions.Name f sens rs TGS3870 TGS4161 TGS825 TGS826 KE-25 SHT15 SHT15 C mp und t be detected Carbon monoxide Carbon dioxide Hydrogen sulfide Ammonia Oxygen Temp. sensor Humidity sensor23

Table- Sensors used for the developed electronic nose

Wireless Electronic Nose(b)Gas Flow Systemy Two solenoid valves control the flow of reference air &

air sample y Reference air - air filtered by activated carbon (valve 1)y Valve 1 open- valve 1 closed-valve 2 open- valve 2 closed

Fig. Gas Flow System24

Wireless Electronic Nose(c) Principal Component Analysis (PCA)y Data from ADC is stored in 2-D array versus sampling y y y y

time Data for each sensor are subtracted by their mean values Covariance matrix of the subtracted data is computed Eigenvectors & Eigenvalues of the covariance matrix are then calculated Then principal components are chosen and featuring vectors are formed

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Wireless Electronic Nose(d) ZigBee Technologyy ZigBee is famous for its low cost, low power consumption y y y y y

& miniaturization Tree topology, with benefits of star & mesh, was used Mostly operates in sleep mode, low power consumption End nodes acquire e-nose data and send them to the router nodes Router nodes combines its own data & send to base nodes Data was sent to database serverFig. Tree Topology26

Wireless Electronic Nose

Fig. Normalized data set from wireless electronic nose.

Fig. PCA plot between PC1 & PC2

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Electronic Nosey Advantages y Detection of poisonous gas is possible y Can be done in real time for long periods y Cheaper than Trained human sniffers y Individuals vary, e-nose don t y Limitations y Time delay between successive tests y Insensitivity to some species y According to application, e-nose has to be changed28

Applicationsy Environmental control (air quality, gas emission levels y y y y y

of factories, chemical plant monitoring etc.) Medical applications (urine, skin, breathe odour analysis, ulcer monitoring etc) Food industry (coffee, fermentation process, identification of bacteria etc.) Defence and security industries (detecting land mines) Pharmaceutics, chemical industry (odour, quality control of pharmaceutical compounds etc.) Semiconductor industrial process29

Future Worky Research is being done on IC E-Noses y Miniaturizing current Technology y Improvement in sensitivity for lower levels of organisms

or smaller samples y Minimizing cost

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Conclusiony 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.

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References[1] T.Pogfay, N.Watthanawisuth, W.Pimpao, A.Wisitsoraat, S. Mongpraneet, T.Lomas & M.Sangworasil: Development of Wireless Electronic Nose for Environment Quality Classification , International conference 0n Electrical Engineering/Electronics, Computer, Telecommunications and Information technology, 19-21 May, 2010 [2] S.H. Saeed, Z. Abbas, B. Gopal: Experimental use of electronic nose for analysis of volatile organic compound , Multimedia, Signal Processing and Communication Technologies, 2009. IMPACT '09, 14-16 March 2009 [3]Nagle H T, Gutierrez-Osuna R, Schiffman: The how and why of electronic nose , IEEE Spectrum, Sep 1998 [4] Lars J. Kangas, Lars H. Liden, Sherif Hashem, Richard T. Kouzes: Electronic noses & their applications , IEEE Technical Applications Conference and Workshops, 1995 [5] http://en.wikipedia.org/wiki/Electronic_nose32

Thank you

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