referencias DECENTES

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Mobile Robotics and Olfaction Lab,

AASS, rebro University

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Achim J. Lilienthal


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# 2MRO'12 A. J. Lilienthal (Jun 6, 2012)

Contents

1. "Classical" Electronic Nose

2. Further Gas Sensing Technologies for Mobile Robots

3. (Signal Processing in Electronic Noses)

4. (Electronic Nose Applications)

5. Literature


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"Classical" Electronic Nose

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[The electronic nose is ] an attempt to mimic the principles of smelling that gives another

view on the whole scene of volatiles compared to its biological inspiration. [Rck et al. 2008]


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1.


o definition [Gardner/Bartlett 1999]

[An electronic nose is ]An instrument that comprises an array of heterogeneous electrochemical gas

sensors with partial specificity and a pattern recognition system capable of

recognizing simple or complex odors.

Electronic Nose Definition


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1.




sensors with partial specificity and a pattern recognition system capable of

recognizing simple or complex odors.



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1.




sensors with partial specificity and a pattern recognition system.



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1.


o electrochemical gas sensors (chemosensors)

devices capable of converting a chemical quantity into an electrical signal large variety of different gas sensors exist (first publications date back to the 1950s)

respond to certain gaseous substances

gaseous substances = true gases or liquids in their vapor phase ("volatiles")

very different from physical sensors

several orders of magnitude more measurands can be detected with chemosensors

Electronic Nose Chemosensors

http://www.emeraldinsight.com/content_images/fig/0870210202009.png

http://www.e2v.com/e2v/assets/Image/Gas Sensors/WEB SIZE ELECTROCHEM GROUP.JPG

http://www.wellgainelectronics.com/ProductImages/17e/FIGARO GAS SENSOR TGS2440.jpg


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sensors with partial specificity and a pattern recognition system.



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[An electronic nose is ]An instrument that comprises an arrayof heterogeneouselectrochemical gas

sensorswith partial specificityand a pattern recognition system.



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1.


o an array of heterogeneous electrochemical gas sensors

Electronic Nose

from [Rck et al 2008]


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1.



with partial specificity

Electronic Nose



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with partial specificityo and a pattern recognition system

Electronic Nose


1


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o introduced to mimic the mammalian olfactory system for smells

[Persaud and Dodd 1982] resembles the biological model

receptorsgas sensors (not fully selective)

information about the smell is in the response signature

Electronic Nose

1


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[Persaud and Dodd 1982]o offers different sensitivity characteristics than the human nose

Electronic Nose

1


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1.



[Persaud and Dodd 1982]o offers different sensitivity characteristics than the human nose

compare human and bee eyes [Rck et al 2008]

Electronic Nose

from Gas Discrimination for Mobile Robots[Trincavelli 2010]

1


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oterm electronic nose is somewhat unfortunate

sensor response patterns cannot be directly correlated with human olfactoryperception

electronic nose systems applications rarely exhibit the enormously broad

applicability spectrum of a human or animal nose (sensitivity, discrimination)

Electronic Nose

1 l i h


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1.

"Classical" Electronic Nose, Chemosensors

o What do we expect from gas sensors?

high sensitivity large dynamic range

high selectivity / specificity to a target analyte

low cross-sensitivity to interferents

perfect reversibility of the physicochemical sensing process

short sensor response and recovery time long-term stability

"a sensor exhibiting all these properties is a largely unrealizable ideal"

[Hierlemann/Gutierrez-Osuna 2008]

Electronic Nose Chemosensors II

1 El i N Ch II


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1.

"Classical" Electronic Nose, Chemosensors

o What do we expect from gas sensors?

high sensitivity large dynamic range

high selectivity / specificity to a target analyte

low cross-sensitivity to interferents

perfect reversibility of the physicochemical sensing process

short sensor response and recovery time long-term stability

high selectivity demands a strong, irreversible interaction between sensor

and target gas

the human receptor cells have a lifetime of only a few weeks!


1 El i N Ch II


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1.

"Classical" Electronic Nose, Sensors used in Robotics

o chemoresistors

Metal Oxide gas sensors (MOS/MOX)


1 El t i N MOX S


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o chemoresistors, metal oxide gas sensors (MOS/MOX)

heating element coated with with semiconductor sensing material

often tin dioxide

sensing material doped with catalytic metal additives

e.g. palladium or platinum

doping changes operating conditionssensor characteristics

Electronic Nose MOX Sensors

Semiconductor Coating (typically SnO2)

Heating Element

1 El t i N MOX S


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absorption of gaseous compounds causes a change of resistance sensitivity depends on the catalytic material, operating conditions, ...

sensing material is heated to 250oC 500oC

increase rate of reactions

prevent absorption of water molecules



Heating Element

1 Electronic Nose MOX Sensors


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1.



absorption of gaseous compounds causes a change of resistance sensitivity depends on the catalytic material, operating conditions, ...

sensing material is heated to 250oC 500oC

increase rate of reactions

prevent absorption of water molecules



Heating Element

1. Electronic Nose MOX Sensors


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semiconductor has sintered polycrystalline surface voltage across heated surface electrical current through grain boundaries




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semiconductor has sintered polycrystalline surface voltage across heated surface electrical current through grain boundaries

absorption of oxygen at the sensor surface increases potential barrier

between grain boundaries

large resistance change!

conductivityrate of redox reactions

with the ambient gas


2. Electronic Nose


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2.

Classical Electronic Nose, Tuning

o variety of sensor specificity tuning possibilities (MOX)

different sensitive materials different doping elements are available

different production processesdifferent morphologies of the sensing layer

different electrodes

different filter layers

different operating temperatures

Electronic Nose



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pros high sensitivity (down to the sub-ppm level for some gases)

usable life-span of three to five years

low susceptibility to changing environmental conditions

changes caused by environmental conditions are smaller than "natural" fluctuations

inexpensive to fabricate

currently most widely used gas sensor in mobile robotic applications




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pros high sensitivity (down to the sub-ppm level for some gases)

usable life-span of three to five years

low susceptibility to changing environmental conditions

inexpensive to fabricate

cons poor selectivity

combustion process not strongly selective to precise structural details of the gas molecules

comparatively high power consumption

due to the high operation temperature

sensors have to be heated before operation (30 - 60 min)

even more in classical e-nose applications (up to days on first use)

variance of the response between individual sensors

slow response

slow recovery after the target gas is removed (15s to 70s)


1. Electronic Nose Chemosensors II


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o chemoresistors

Metal Oxide gas sensors (MOS/MOX) Conducting Polymer Gas Sensors


1. Electronic Nose Conducting Polymer Sensors


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o chemoresistors, Conducting Polymer Gas Sensors

measurand = resistance of the surface layer semiconductor thin polymer film

volatile analyte induces expansion of the polymer composite

increase in electrical resistance

response depends largely on the rate of diffusion of the vapour into the polymer

response time between several seconds to several minutes

Electronic Nose Conducting Polymer Sensors

1. Electronic Nose Conducting Polymer Sensors


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o chemoresistors, Conducting Polymer Gas Sensors

pros comparatively easy to prepare

but conditions have to be carefully controlled and chemicals have to be suitably purified in

order to achieve reproducibleresults

wide range of materials with varying sensitivity can be synthesised

can operate at room temperature low power consumption

linear responses for a wide range of gases

cons

sensitivity is approx. one order of magnitude lower than that of MOX sensors

effects of aging sensor drift

a poor understanding of the mechanism behind the conducting polymers

Electronic Nose Conducting Polymer Sensors

1. Electronic Nose Chemosensors II


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o chemoresistors

Metal Oxide gas sensors (MOS/MOX) Conducting Polymer Gas Sensors

o gravimetric

Quartz Microbalance sensors (QMB)


1. Electronic Nose Acoustic Wave Sensors


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o chemoresistors, Quartz Microbalance sensors (QMB/QCM)

piezoelectronic substrate (usually quartz) application of alternating electric field generates elastic wave in the quartz crystal

coating with a specific affinity

absorbed molecules perturb the propagation of the acoustic waves

due to the effect of the added mass

by changing the viscoelastic properties of the coating layer shift of the fundamental frequency of the quartz crystal

measured as the output of the sensor

Electronic Nose Acoustic Wave Sensors

http://www.tectra.de/_icons/QMB head.JPG



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pros rapid response

time required for recovery usually shorter than for MOX sensors

low power consumption

long term stability, long lifetime

cons comparatively low sensitivity

limited robustness to variations in humidity

complex fabrication processes

poor signal to noise ratio




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pros rapid response

time required for recovery usually shorter than for MOX sensors

low power consumption

long term stability, long lifetime

cons comparatively low sensitivity

limited robustness to variations in humidity

complex fabrication processes

poor signal to noise ratio

High Frequency Fundamental (HFF) Quartz crystals [Kreutz et al. 2006]


2


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Further

Gas Sensing Technologies

for Mobile Robots

2

2. Further Gas Sensing Technologies (for Robots?)


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Beyond the Classical Electronic Nose

o optical sensor systems

g g ( )

2. Optical Sensor Systems


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Optical Sensor Systems

o measures modulation of light properties

e.g. absorption in a specific frequency range

p y

2. Optical Sensor Systems RMLD


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o Remote Methane Leak Dector (RMLD, Sewerin)

exclusively developed for detecting methane gas, shows no cross-sensitivityto other hydrocarbons

detection principle

measurement specifications

laser specifications

p y

Transceiver

Controller



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detection principle

TDLAS (Tunable Diode Laser Absorption Spectroscopy)



p y



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detection principle





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detection principle



class 1 laser (no eye protection required) conical beam, width 0.56 m at 30 m



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o mass spectrometry (MS)

2. Mass Spectrometry (MS)


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Mass Spectrometry

o ionization of compounds

http://antoine.frostburg.edu/chem/senese/101/atoms/images/ms3.jpg



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Mass Spectrometry


o separation according to m/z with electric or magnetic field




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Mass Spectrometry



o detection of the ions with an electron multiplier




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Mass Spectrometry



o detection of the ions with an electron multiplier

o disadvantages for robotics

ionization unit required

vacuum is required

not very convenient

costly



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o mass spectrometryo ion mobility spectrometry (IMS)

2. Ion Mobility Spectrometry (IMS)


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Ion Mobility Spectrometry

o separation of ions by m/z and mobility

Strukturuntersuchungen an (C60)n+-Clustern mit der Methode der Gasphasen-Ionenchromatographie [Lilienthal 1998]

2.

Ion Mobility Spectrometry (IMS)


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ionization of compounds


2.



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separation of m/z


2.



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separation of m/z

pulsed introduction

to a drift region

larger ions with greater

collision cross section

are slower due to

more collisions


2.



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separation of m/z

pulsed introduction

to a drift region

detection of ion current


2. Ion Mobility Spectrometry (IMS)


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separation of m/z

pulsed introduction

to a drift region

detection of ion current

o disadvantages for robotics ionization unit required

ion-ion interaction causes problems in complex mixtures

drift cell with inert gas required (isolated from atmospheric air)

not very convenient

costly

2. Photoionization Detector (PID)


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Photoionization Detector (VOC monitor)

o MS/IMS without m/z and mobility separation

2.

Photoionization Detector (PID)


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Photoionization Detector (VOC monitor)

o MS/IMS without m/z and mobility separation

o

ionization with UV lamp max. 11.7 eV in RAE PIDs (ethanol, acetone, methanol)

cannot detect methane (IP between 12.6 and 13.6 eV [URL])

o detection of current

o pros

quick response to a wide range of gases

calibrated readings if there is only one, known compound

o cons

not suitable for classification

too bulky (?) expensive

3
http://webbook.nist.gov/cgi/cbook.cgi?ID=C74828&Mask=20http://webbook.nist.gov/cgi/cbook.cgi?ID=C74828&Mask=20


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Signal Processing in

Electronic Noses

3

3. E-Nose Signal Processing


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Components of an E-Nose Approach

o sampling system

o

sensor array (physical or virtual)o data evaluation algorithms

reference data set

Tasks

o detectiono discrimination

o identification

o quantification



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o sampling system

o

sensor array (physical or virtual) sensors with partial selectivity

output of sensors is usually one feature per sensor (at a time)

resistance, fundamental frequency shift, etc.

preferably during an equilibrium-type or steady-state-type situation

sensor array corresponds to feature space



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o sampling system

o

sensor array (physical or virtual) output of sensors is usually one feature per sensor (at a time)

sensor array corresponds to feature space

o data evaluation algorithms

data analysis using e.g. pattern recognition tools

4
http://../Books/Bishop_2006-Pattern_Recognition_and_Machine_Learning-Springer-ISBN_0387310738.pdf


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Electronic Nose Applications

4. Electronic Nose Applications


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Application Areas

o food and beverage control (human sense of smell)

o

fire warning (

human sense of smell)o pollution monitoring (human sense of smell)

environmental monitoring

o detection of hazardous substances and explosives

(securitymacrosmatic mammals such as dogs)

o disease diagnosis

lung cancer

bacteria in blood

o etc.



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Application Areas

o food and beverage control (human sense of smell)

o

fire warning (

human sense of smell)o pollution monitoring (human sense of smell)

environmental monitoring

o detection of hazardous substances and explosives

(securitymacrosmatic mammals such as dogs)

o disease diagnosis

lung cancer

bacteria in blood

o etc.



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Environmental Monitoring

o detection of toxic compounds in the ambient atmosphere

at concentrations which will not have an immediate effect but are a long-

term danger for human health

carbon monoxide, nitrogen oxides, sulfur oxides, volatile organic compounds,

ammonia, ozone, and particulate matter

compounds that are simply unpleasant



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o

analytical instruments do not allow dense, continuous samplingo however, using e-noses is very challenging

complex mixtures

low detection thresholds

sampling (where? when?)

samples must be representative and independent of variable ambient conditions

knowledge of spatial and time patterns of concentrations is important

changes in temperature and humidity

sample pre-treatment and parametric compensation



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o

analytical instruments do not allow dense, continuous samplingo however, using e-noses is very challenging

complex mixtures

low detection thresholds

sampling (where? when?)

samples must be representative and independent of variable ambient conditions

knowledge of spatial and time patterns of concentrations is important

changes in temperature and humidity

sample pre-treatment and parametric compensation



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o for application the sensitivity of the electronic nose to the target

substances and to potential interferents has to be known



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o for application the sensitivity of the electronic nose to the target

substances and to potential interferents has to be known

[Rck et al. 2008]

5


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Literature

4. Literature


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Literature

o [Pearce et al. 2003]

Handbook of Machine Olfaction

Chapter 4

4. Literature


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Literature


o

[Rck et al. 2008] Electronic Nose: Current Status andFuture Trends,

Chem. Rev. 2008, 108, 705-725

4. Literature


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Literature


o

[Rck et al. 2008]o [Hierlemann/Gutierrez-Osuna 2008]

Higher-Order Chemical Sensing,

A. Hierlemann and

R. Gutierrez-Osuna.

Chem. Rev. 2008, 108, 563-613.

4. Literature


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Literature


o

[Rck et al. 2008]o [Hierlemann/Gutierrez-Osuna 2008]

o [Gardner/Bartlett 1999]

Electronic Noses

Principles and Applications,

J. W. Gardner and P. N. Bartlett.

Oxford Science Publications, 1999.

4. Literature


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Literature


o [Rck et al. 2008]

o [Hierlemann/Gutierrez-Osuna 2008]

o [Persaud and Dodd 1982]

Analysis of Discrimination Mechanisms in the Mammalian Olfactory System

using a Model Nose.Nature, 1982, 299, 352355.

o [Kreutz et al. 2006] High Frequency QuartzMicro Balances: A Promising Path to Enhanced

Sensitivity of Gravimetric Sensors. Sensors 2006, 6, 335340.


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Mobile Robotics and Olfaction Lab,

AASS, rebro UniversityAchim J. Lilienthal

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