[attachment=1651]

ELECTRONIC NOSE
ABSTRACT
The perception of volatile compounds by the human nose is of great importance in evaluating the quality of foods. Therefore, it is not surprising that repeated efforts have been made over the years to introduce instruments operating on a similar principle as the human nose: the electronic nose is an instrument that encloses the human sensitivity to the objectivity of the instrumental response and supplies results similar to the human nose and in short time.
An electronic nose is an instrument which comprises an array of electronic chemical sensors with partial specificity and an appropriate pattern recognition system capable of recognising simple or complex odours. 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.
Research has been carried out into the use of thin and thick film semiconducting (inorganic and organic) materials for odour sensing. Research effort is now centered upon the use of arrays of metal oxide and conducting polymer odour sensors. The latter are particularly exciting because their molecular structure can be engineered for a particular odour-sensing application. The electronic nose finds wide applications in the food industry. Future developments in the use of hybrid micro sensor arrays and the development of adaptive artificial neural networking techniques will lead to superior electronic noses.


By,
Deena Davies,
IV year, Biomedical Engineering Department
Sahrdaya College of Engineering And Technology,
Kodakara, Thrissur, Kerala.

INTRODUCTION
The perception of volatile compounds by the human nose is of great importance in evaluating the quality of foods. Therefore, it is not surprising that repeated efforts have been made over the years to introduce instruments operating on a similar principle as the human nose: the electronic nose or simply the E-nose is an instrument that encloses the human sensitivity to the objectivity of the instrumental response and supplies results similar to the human nose and in short time.
An electronic nose is Ëœan instrument which comprises an array of electronic chemical sensors with partial specificity and an appropriate pattern recognition system capable of recognising simple or complex odoursâ„¢. 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.
The "electronic nose" is a relatively new tool that may be used for safety, quality, or process monitoring, accomplishing in a few minutes procedures that may presently require days to complete. Therefore the main advantage of this instrument is that in a matter of seconds, it delivers objective, reproducible aroma discrimination with sensitivity comparable to the human nose for most applications. The term "electronic nose" was first used in a jocular sense with sensor arrays in the 1980's. As the technology developed, it became apparent that the animal and human olfactory systems operate on the same principle: A relatively small number of nonselective receptors allow the discrimination of thousands of different odours.
Research has been carried out into the use of thin and thick film semiconducting (inorganic and organic) materials for odour sensing. Research effort is now centered upon the use of arrays of metal oxide and conducting polymer odour sensors.
HUMAN NOSE vs. ELECTRONIC NOSE

ELECTRONIC NOSE INSTRUMENTATION
An electronic nose like human sensory systems, it incorporates:
¢ Chemical sensors (10 MOSFET and 5 MOS) as we have human olfactory receptors in our olfactory region.
¢ A data-processing system (NST Senstool) as we have our brain.
A MOSFET sensor rely on a change of electrostatic potential. They respond exclusively to molecules that dissociate hydrogen on the catalytic metal surface (such as amines, aldeids, esthers, chetons, aromatics ed alchols) and they work at the temperature of 140-170°C. When polar compounds interact with this metal gate, the electric field, and thus the current flowing through the sensor, are modified. The recorded response corresponds to the change of voltage necessary to keep a costant present drain current.

A MOS sensor rely on change of conductivity induced by the adsorption of gases. Due to the high operating temperature (300-400°C) the organic volatiles (such as satured hydrocarbons, NO, CO etc.) trasferred to the sensors are totally combusted to carbon dioxide and water on the surface of the metal oxide, leading to a change in the resistance.
NST Senstool software offers three methods for analyzing sensors input:
¢ PCA: Principal Component Analysis
¢ PLS: Partial Least Square Regression
¢ ANN: Artificial Neural Network
They enable to:
¢Get an overview of the data (PCA and PLS)
¢Predict properties of the samples (PLS e ANN
PCA is a rotation-projection method that helps visualizing the information contained in a large data set. It is a transformation in which many original dimensions are transformed into another coordinate system with fewer dimensions.
PLS is a regression model which use Principal Components and in which we must give a property of the samples such as class or quantitative value.
Artificial neural networks are the most powerful type of data processing technique being employed in Electronic Nose instruments. ANNs are self-learning; the more data presented, the more discriminating the instrument becomes. By running many standard samples and storing results in computer memory, the application of ANN enables the Electronic Nose to "understand" the significance of the sensor array outputs better and to use this information for future analysis.
ANNs allow the Electronic Nose to function in the way a brain functions when it interprets responses from olfactory sensors in the human nose. The ANN's processing elements (or nodes) can be compared to the neurons in the brain. "Learning" is achieved by varying the emphasis, or weight, that is placed on the output of one sensor versus another. ANNs also can be trained to compensate for small response changes that occur when sensors degrade over time. Ideally, a sensor array would respond to a specific sample with the same precision over a long period of time. However, sensors can degrade with prolonged use and the output can vary. ANNs can correct for this problem.
As the organic vapors pass over the sensor array each sensor responds with a certain selectivity. These patterns need to be further processed. Electronic Nose Technology (ENT) is the combination of sensor arrays linked with advanced statistical and neural network software that provides a visual image of an odour, or how an odour relates to other odours. This relationship could represent good “ bad, pass “ fail, new “ old, or the system can be trained to recognize attributes such as green, fruity, floral or spoiled. ENT correlates exceedingly well with both sensory and tradition analytical techniques and ENT can combine both elements in a single analysis.
A number of prototype electronic noses have been developed by the electronic nose research group. There are several laboratory-based instruments, one employing an array of metal oxide sensors, and another employing an array of conducting polymer sensors. This research has led to the production of two desk-top sized electronic nose instruments. Several portable instruments have also been designed and built. These include a 4-element tin oxide electronic nose, a 6-element tin oxide electronic nose, and four 12-element polymer electronic noses.

The E-Nose is best suited for matching complex samples with subjective endpoints such as odor or flavor. For example, when has milk turned sour? Or, when is a batch of coffee beans optimally roasted? The E-Nose can match a set of sensor responses to a calibration set produced by the human taste panel or olfactory panel routinely used in food science. The E-Nose is especially useful where consistent product quality has to be maintained over long periods of time, or where repeated exposure to a sample poses a health risk to the human olfactory panel. Although the E- Nose is also effective for pure chemicals, conventional methods are often more practical.
APPLICATIONS
The electronic nose finds wide applications in the food industry. It is used to detect the bacterial growth on foods such as meat and fresh vegetables. It can be used to test the freshness of fish. It is used in the process control of cheese, sausage, beer, and bread manufacture. Other applications include Identification of spilled chemicals in commerce (for U.S. Coast Guard), Quality classification of stored grain, Diagnosis of ulcers by breath tests, Detection and diagnosis of pulmonary infections (e.g., TB or pneumonia), Identification of source and quality of coffee, Monitoring of roasting process, and so on.
FUTURE DEVELOPMENTS
There are numerous potential applications of electronic noses from the product and process control to the environmental monitoring of pollutants and diagnosis of medical complaints. However, this requires the developments of application-specific electronic nose technology, that is electronic noses that have been designed for a particular application. This usually involves the selection of the appropriate active material, sensor type and pattern recognition scheme. The work has led to several commercial instruments, one employing commercial tin oxide sensors (Fox 2000, Alpha MOS, France) and another employing conducting polymer sensors (NOSE, Neotronics Ltd, UK). Future developments in the use of hybrid microsensor arrays and the development of adaptive artificial neural networking techniques will lead to superior electronic noses.
The major areas of research being carried out in this field are:
1. Improved sensitivity for use with water quality and sensitive microorganism detection applications.
2. Identification of microorganisms to the strain level in a number of matrices, including food.
3. Improvement in sensitivity of the E-Nose for lower levels of organisms or smaller samples.
4. Identification of infections such as tuberculosis in noninvasive specimens (sputum, breath).
5. Development of sensors suitable for electronic nose use, and evaluation of unexploited sensors.
CONCLUSION
Advantages of the electronic nose can be attributed to its rapidity, objectivity, versatility, non requirement for the sample to be pretreatment, easy to use etc. And now scientists at the University of Rome have developed a sensor, which, they claim, can detect those chemicals flowing out of a cancerous lung. Their tests, on a group of 60 people - half with lung cancer - pinpointed every single cancer patient. They suggested that an 'e-nose' could one day form the basis of a screening test for smokers and others at risk of lung disease. The only way of doing this reliably at the moment is to use a bronchoscope to look directly at the insides of the lungs for signs of cancer.

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respected sir/mam
I am student of bachelor of technology from electronics and communication enggineering.i want more description about electronic nose mainly about its sensors like calorimetric sensors,conducting sensors,piezoelectric sensors,chemical sensors.
please mail me description about these things .
thank you.

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my email address is ankigupts[at]gmail.com.
thank you.

hi
please go through the following page link for more details about electronic nose.

http://studentbank.in/report-seminars-re...ronic-nose

[attachment=5010]

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Introduction

Electronics nose

Over the last decade, “electronic sensing” or “e-sensing” technologies have undergone important developments from a technical and commercial point of view. The expression “electronic sensing” refers to the capability of reproducing human senses using sensor arrays and pattern recognition systems. Since 1982, research has been conducted to develop technologies, commonly referred to as electronic noses, that could detect and recognize odors and flavors. The stages of the recognition process are similar to human olfaction and are performed for identification, comparison, quantification and other applications. However, hedonic evaluation is a specificity of the human nose given that it is related to subjective opinions. These devices have undergone much development and are now used to fulfill industrial needs.

[attachment=6191]

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ABSTRACT
The harnessing of electronics to measure odor is greatly to be desired. Human panels backed up by gas chromatography and mass spectrometry are helpful in quantifying smells, but they time are consuming, expensive and seldom performed in real time in the field. So it is important that these traditional methods give way to a speedier procedure using and electronic nose composed of gas sensors. Electronic nose or E-noses are the systems that detect and identify odours and vapours, typically linking chemical sensing devices with signal processing, pattern recognition and artificial intelligence techniques which enable uses to readily extract relevant and reliable information.
INTRODUCTION
The electronics field is developing at a fast rate. Each day the industry is coming with new technology and products. The electronic components play a major role in all fields of life. The scientists had started to mimic the biological world. The development of artificial neural network (ANN), in which the nervous system is electronically implemented is one among them. The scientists realized the importance of the detection and identification of odor in many fields. In human body it is achieved with the help of one of the sense organ, the nose. So scientists realized the need of imitating the human nose. The concept of the electronic nose appeared for the first time in a nature paper by Persuade and Dodd (1982). The authors suggested and demonstrated with a few examples that gas sensor array responses could be analyzed with artificial neural networks thereby increasing sensitivity and precision in analysis significantly. This first publication was followed by several methodological papers evaluating different sensor types and combinations. The scientists saw the last advances in the electronic means of seeing and hearing. Witnessing this fast advances they scent a marker for systems mimicking the human nose. The harnessing of electronics to measure odor is greatly desired. Human panels backed by gas chromatography (GC)/ mass spectroscopy (MS) are helpfulin quantifying smells. The human panels are subject to fatigue and inconsistencies. While classical gas chromatography (GC)/ mass spectrograph (MS) technique separate quantify and identify individual volatile chemicals, they cannot tell us if the components have an odour. Also they are very slow. So it is important that faster methods must give way to speedier procedure using an electronic nose composed of gas sensory. The E-nose was developed not to replace traditional GC/MS and sensory techniques. The E-nose was sensitive and as discriminating as the human nose, and it also correlates extremely with GC/MS data. The electronic nose allows to transfer expert know ledged from highly trained sensory panels and very sophisticated R&D analytical techniques to the production floor for the control of quality. Although the human nose is very sensitive, it is highly subjective. The E – nose offers objectivity and reproducibility. The electronic nose technology goes several steps ahead of the conventional gas sensors. The electronics nose system detects and sensing devices with pattern recognition sub system. The electronic nose won quickly considerable interest in food analysis for rapid and reliable quality classification in manufacturing testing. Later, the electronic noses have also been applied to classification of micro organisms and bio-reactor monitoring. Even though the electronic nose resembles its biological counter part nose too closely the label “electronic nose” or “E-nose” has been widely accepted around the world.

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[attachment=8340]

Submitted by,

K.MANO & K.KAVITHA

PSY Engineering College.




SYNOPSIS


Introduction
Human nose vs. Electronic nose
Advantages over human sniffers
Sensors in E-nose
E-nose Instrumentation
Portable E-nose
Food quality analysis
Health monitoring
Human body odour analysis
Humidity control
Applications
Future development
Conclusion

EMBEDDED ELECTRONIC NOSE



INTRODUCTION

An electronic nose is “an instrument which comprises an array of electronic chemical sensors with partial specificity and an appropriate pattern recognition system capable of recognizing simple or complex odours”. The "electronic nose" is a relatively new tool that may be used for safety, quality, or process monitoring, accomplishing in a few minutes procedures that may presently require days to complete. Therefore the main advantage of this instrument is that in a matter of seconds, it delivers objective, reproducible aroma discrimination with sensitivity comparable to the human nose for most applications.

HUMAN NOSE vs. ELECTRONIC NOSE

Each and every part of the electronic nose is similar to human nose. The function of inhaling is done by the pump which leads the gas to the sensors. The gas inhaled by the pump is filtered which in the human is the mucus membrane. Next comes the sensing of the filtered gas, which will be done by the sensors i.e., olfactory epithelium in human nose. Now in electronic nose the chemical retain occurs which in human body is enzymal reaction. After this the cell membrane gets depolarised which is similar to the electric signals in the electronic nose. This gets transferred as nerve impulse through neurons i.e., neural network and electronic circuitries.







ADVANTAGES OVER HUMAN SNIFFERS

The human sniffers are costly when compared to electronic nose. It is because these people have to be trained. This is a time consuming that a construction of an electronic nose. Now for the confirmation of the values obtained from a sniffer the result obtained from the sniffer has to be compared with some other sniffer’s value. And here there are great chances of difference in the values got by each individual. Detection of hazardous or poisonous gas is not possible with a human sniffer. Thus taking into consideration all these cases we can say that electronic nose is highly efficient than human sniffer.


DIFFERENT TYPES OF SENSORS

There are different types of electronic noses which can be selected according to requirements. Some of the sensors available are calorimetric, conducting, piezoelectric etc. Conducting type sensors can again be sub divided into metal oxide and polymers. In this type of sensors the functioning is according to the change in resistance. The sensor absorbs the gas emitted from the test element and this results in the change of resistance correspondingly. According to the Resistance-Voltage relation V=I*R. Here ‘V’ is the voltage drop, ‘R’ is the resistance of the sensor and ‘I’ is the current through it. By this relation as resistance changes the voltage drop across the sensor also change. This voltage is measured and is given to the circuit for further processes. The voltage range for using metal oxide sensor in from 200°C to 400°C. The working principle of polymer sensor is same as that of metal oxide sensor .Calorimetric sensors are preferable only for combustible species of test materials. Here the sensors measure the concentration of combustibles species by detecting the temperature rise resulting from the oxidation procession a catalytic element.




ELECTRONIC NOSE INSTRUMENTATION

A data-processing system (NST Senstool) as we have our brain.
A MOSFET sensor rely on a change of electrostatic potential. They respond exclusively to molecules that dissociate hydrogen on the catalytic metal surface (such as amines, aldeids, esthers, chetons, aromatics ed alcohols) and they work at the temperature of 140-170°C. When polar compounds interact with this metal gate, the electric field, and thus the current flowing through the sensor, are modified. The recorded response corresponds to the change of voltage necessary to keep a constant present drain current.

A MOS sensor rely on change of conductivity induced by the adsorption of gases. Due to the high operating temperature (300-400°C) the organic volatiles (such as satured hydrocarbons, NO, CO etc.) transferred to the sensors are totally combusted to carbon dioxide and water on the surface of the metal oxide, leading to a change in the resistance.
NST Senstool software offers three methods for analyzing sensors input:

•PCA: Principal Component Analysis
•PLS: Partial Least Square Regression
•ANN: Artificial Neural Network


IPNOSE: A PORTABLE ELECTRONIC NOSE BASED ON EMBEDDED
TECHNOLOGY FOR INTENSIVE COMPUTATION AND TIME DEPENDENT
SIGNAL PROCESSING

Here we suggest the integration of a small form factor computer for an electronic nose
system. This concept allows us to seamlessly implement arbitrary temperature modulation for tin-oxide sensors, remote connectivity, large Data storage, and complex signal processing.Gas sensors used in electronic noses are based on broad selectivity profiles, mimicking the responses of olfactory receptors in the biological olfactory system. The basic building blocks of a generic electronic-nose systems include sample delivery, sensor chamber, signal transduction and acquisition, data preprocessing, feature extraction and feature classification. In conventional systems, the processing module is a personal computer separated from the remaining parts of the system. This module is responsible for data preprocessing, feature extraction and classification. Significant efforts are required to improve the overall performance of the instrument, and every component must be given careful consideration.
MONITORINGOPEN ACCESS
FOOD ANALYSIS

The electronic nose finds wide applications in the food industry. It is used to detect the bacterial growth on foods such as meat and fresh vegetables. It can be used to test the freshness of fish. It is used in the process control of cheese, sausage, beer, and bread manufacture. Other applications include Identification of spilled chemicals in commerce (for U.S. Coast Guard), Quality classification of stored grain, Diagnosis of ulcers by breath tests, Detection and diagnosis of pulmonary infections (e.g., TB or pneumonia), Identification of source and quality of coffee, Monitoring of roasting process, and so on.

The use of ENs for food quality analysis tasks is twofold. ENs is normally used to discriminate different classes of similar odour-emitting products. In particular ENs already served to distinguish between different coffee blends and between different coffee roasting levels and beverages. This is because the separation achieved by the gas chromatographic technique is complemented by the high sensitivity of mass spectroscopy and its ability to identify the molecules eluting from the column on the basis of their fragmentation patterns. Detection limits as low as 1 ppb (parts per billion) are frequently reached. Commercial coffees are blends, which, for economic reasons, contain (monovarietal) coffees of various origins.





HEALTHCARE MONITORING

Many new applications await in such area as healthcare monitoring, biometrics and cosmetics. In principles, the human body dynamically generates unique patterns of volatile organic compounds (VOCs) under diverse living conditions such as eating, drinking, sexual activities, health or hormonal status. These VOCs released from the human body can give some information about diseases, behavior, emotional state and health status of a person. The human odor is released from various parts of body and exists in various forms such as exhalation, armpits, urine, stools, farts or feet. E-nose can diagnose the urine odor of the patients with kidney disorders.

HUMAN BODY ODOUR ANALYSIS

An electronic nose (E-nose) has been designed and equipped with software that can detect and classify human armpit body odor. An array of metal oxide sensors was used for detecting volatile organic compounds. The measurement circuit employs a voltage divider resistor to measure the sensitivity of each sensor. This E-nose was controlled by in-house developed software through a portable USB data acquisition card with a principle component analysis (PCA) algorithm implemented for pattern recognition and classification. The E-nose is still able to recognize people, even after application of deodorant. In conclusion, this is the first report of the application of an E-nose for armpit odor recognition.

HUMIDITY CONTROL

Most chemical gas sensors are sensitive to humidity. Therefore, if two identical samples with a different humidity are measured, the results can be different. In our work, we propose two methods as solutions to this problem. The first is a hardware-based method, where the sample was handled so as to have almost the same humidity as the background. Under such condition, the humidity signals will be equivalent for the sample and the reference, thereby only signals from the odors of interest result. To produce a constant humidity background, the carrier gas was directed to flow through a liquid water container that is immersed in a temperature-controlled heat bath. The temperature of the heat bath can be adjusted until the generated humidity reaches the desired value. humidity.

APPLICATIONS OF ELECTRONIC NOSES

There are various applications in which an electronic nose may be used.
• Environmental monitoring
• Monitoring of air, water and land.
• Medical Diagnostics and Health Monitoring
• Breath Monitoring
• Eye Infection
• Medical Environmental Monitoring
• Leg Ulcers
• Cultured Bacteria
• Food and Beverage Applications
• Quality and process monitoring of fruits, vegetables, meat, fish, brewery, tea, coffee and so on.
• Automotive and Aerospace Applications
• Detection of hazardous gas within automobiles, spacecrafts.
• Narcotic Detection.
• Application in Cosmetics and Fragrance Industry
• Detection of Explosives








FUTURE DEVELOPMENTS

Future developments in the use of hybrid micro sensor arrays and the development of adaptive artificial neural networking techniques will lead to superior electronic noses.
The major areas of research being carried out in this field are:
1. Improved sensitivity for use with water quality and sensitive microorganism detection applications.
2. Identification of microorganisms to the strain level in a number of matrices, including food.
3. Improvement in sensitivity of the E-Nose for lower levels of organisms or smaller samples.
4. Identification of infections such as tuberculosis in noninvasive specimens (sputum, breath).
5. Development of sensors suitable for electronic nose use, and evaluation of unexploited sensors.


CONCLUSIONS

Researches are still going on to make electronic nose much more compact than the present one to make it more compact and to make electronic nose I.C.s. In future we might be able to manufacture olfactory nerves.
Advantages of the electronic nose can be attributed to its rapidity, objectivity, versatility, non requirement for the sample to be pretreatment, easy to use etc.

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PRESENTED BY:
Igor V. Aristov

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[attachment=13195]
The Electronic Nose:
A Multivariate Approach
The tasks of this report:
To inform on chemometrics studies in Voronezh
To describe the results of one research project
Scientific interests
Analytical Chemistry
Electrochemistry
Separation methods
Applied Statistics
The Problem
We want to distinguish vapors of chemical substances in air using a cross-selectivity multisensor detector
The “Electronic Nose”
Unit for gas analysis with many cross-selectivity sensors.
The “Electronic Nose”: a scheme
Experimental equipment
Scheme of Analytical Information
Electronic Nose with 14 cross-selectivity sensors
Sorbates
Benzol
Aniline
o-Methyl Aniline
m-Methyl Aniline
p-Methyl Aniline
Analytical signals
DF; frequency difference
a; capacity
t0.5; time of half sorption
Vapor Print TM
Vapor Print TM
Discriminant Analysis
Discriminant Analysis
Classification
Scheffe test (t0.5)
Scheffe test (DF)
Scheffe test (a)
In The Nearest Future
Optimization of sensors number
Multivariate calibration

[attachment=14549]
INTRODUCTION
The electronics field is developing at a fast rate. Each
day the industry is coming with new technology and
products. The electronic components play a major role in
all fields of life. The scientists had started to mimic the
biological world. The development of artificial neural
network (ANN), in which the nervous system is
electronically implemented is one among them.
The scientists realized the importance of the
detection and identification of odor in many fields. In
human body it is achieved with the help of one of the
sense organ, the nose. So scientists realized the need of
imitating the human nose. The concept of the electronic
nose appeared for the first time in a nature paper by
Persuade and Dodd (1982). The authors suggested and
demonstrated with a few examples that gas sensor array
responses could be analyzed with artificial neural
networks thereby increasing sensitivity and precision in
analysis significantly. This first publication was followed
by several methodological papers evaluating different
sensor types and combinations.
The scientists saw the last advances in the electronic
means of seeing and hearing. Witnessing this fast
advances they scent a marker for systems mimicking the
human nose. The harnessing of electronics to measure
odor is greatly desired. Human panels backed by gas
chromatography (GC)/ mass spectroscopy (MS) are helpful
Electronic Nose
in quantifying smells. The human panels are subject to
fatigue and inconsistencies. While classical gas
chromatography (GC)/ mass spectrograph (MS) technique
separate quantify and identify individual volatile
chemicals, they cannot tell us if the components have an
odour. Also they are very slow. So it is important that
faster methods must give way to speedier procedure using
an electronic nose composed of gas sensory. The E-nose
was developed not to replace traditional GC/MS and
sensory techniques. The E-nose was sensitive and as
discriminating as the human nose, and it also correlates
extremely with GC/MS data. The electronic nose allows to
transfer expert know ledged from highly trained sensory
panels and very sophisticated R&D analytical techniques
to the production floor for the control of quality. Although
the human nose is very sensitive, it is highly subjective.
The E – nose offers objectivity and reproducibility.
The electronic nose technology goes several steps
ahead of the conventional gas sensors. The electronics
nose system detects and sensing devices with pattern
recognition sub system. The electronic nose won quickly
considerable interest in food analysis for rapid and reliable
quality classification in manufacturing testing. Later, the
electronic noses have also been applied to classification of
micro organisms and bio-reactor monitoring. Even though
the electronic nose resembles its biological counter part
nose too closely the label “electronic nose” or “E-nose” has
been widely accepted around the world.
Electronic Nose
THE BIOLOGICAL NOSE
To attempt to mimic the human apparatus,
researchers have identified distinct steps that characterize
the way humans smell. It all begins with sniffing, which
moves air samples that contain molecules of odors past
curved bony structures called turbinate. The turbinate
create turbulent airflow patterns that carry the mixture of
volatile compounds to that thin mucus coating of the
nose’s olfactory epithelium, where ends if the nerve cells
that sense odorants.
The volatile organic compounds (VOCs) basic to
odors reach the olfactory epithelium in gaseous form or
else as a coating on the particles that fill the air we
breathe. Particles reach the olfactory epithelium not only
from the nostrils but also from the mouth when food is
chewed.
As VOCs and particles carrying VOCs pass over the
mucus membrane lining the nose, they are trapped by the
mucus and diffuse through to the next layer, namely, the
epithelium, where the sensory cells lie in wait. The cells
are covered in multiple cilia- hair like structures with
receptors located on the cells outer membranes. Olfactory
cells are specialized neurons that are replicated
approximately every 30 days.

[attachment=15038]
1. INTRODUCTION
ELECTRONIC Noses (EN), in the broadest meaning, are instruments that analyze gaseous mixtures for discriminating between different (but similar) mixtures and, in the case of simple mixtures, quantify the concentration of the constituents. ENs consists of a sampling system (for a reproducible collection of the mixture), an array of chemical sensors, Electronic circuitry and data analysis software. Chemical sensors, which are the heart of the system, can be divided into three categories according to the type of sensitive material used: inorganic crystalline materials (e.g. semiconductors, as in MOSFET structures, and metal oxides); organic materials and polymers; biologically derived materials.
The use of ENs for food quality analysis tasks is twofold. ENs is normally used to discriminate different classes of similar odour-emitting products. In particular ENs already served to distinguish between different coffee blends and between different coffee roasting levels. On the other hand, ENs can also be used to predict sensorial descriptors of food quality as determined by a panel (often one generically speaks of correlating EN and sensory data). ENs can therefore represent a valid help for routine food analysis.
The combination of gas chromatography and mass spectroscopy (GC-MS) is by far the most popular technique for the identification of volatile compounds in foods and beverages. This is because the separation achieved by the gas chromatographic technique is complemented by the high sensitivity of mass spectroscopy and its ability to identify the molecules eluting from the column on the basis of their fragmentation patterns. Detection limits as low as 1 ppb (parts per billion) are frequently reached. The main drawbacks of the approach are, however, the cost and complexity of the instrumentation and the time required to fully analyze each sample (around one hour for a complete chromatogram). Comparatively, ENs are simpler, cheaper devices. They recognize a fingerprint, that is global information, of the samples to be classified. For food products, the sensory characteristics determined by a panel are important for quality assessment. While man still is the most efficient instrument for sensorial evaluation, the formation of a panel of trained judges involves considerable expenses.
Commercial coffees are blends, which, for economic reasons, contain (monovarietal) coffees of various origins. For the producers the availability of analysis and control techniques is of great importance. There exists a rich literature on the characterization of coffee using the chemical profile of one of its fractions, such as the headspace of green or roasted beans or the phenolic fraction. In the literature up to 700 diverse molecules have been identified in the headspace. Their relative abundance depends on the type, provenance and manufacturing of the coffee. It is to be noticed that none of these molecules can alone be identified as a marker. On the contrary one has to consider the whole spectrum, as for instance the gas chromatographic profile.
2. COMPARISION OF ELECTRONIC NOSE WITH BIOLOGICAL NOSE
Each and every part of the electronic nose is similar to human nose. The function of inhaling is done by the pump which leads the gas to the sensors. The gas inhaled by the pump is filtered which in the human is the mucus membrane. Next comes the sensing of the filtered gas, which will be done by the sensors i.e., olfactory epithelium in human nose. Now in electronic nose the chemical retain occurs which in human body is enzymal reaction. After this the cell membrane gets depolarised which is similar to the electric signals in the electronic nose. This gets transferred as nerve impulse through neurons i.e., neural network and electronic circuitries.
3.DIFFERENT TYPES OF SENSORS
There are different types of electronic noses which can be selected according to requirements. Some of the sensors available are calorimetric, conducting, piezoelectric etc. Conducting type sensors can again be sub divided into metal oxide and polymers. In this type of sensors the functioning is according to the change in resistance. The sensor absorbs the gas emitted from the test element and this results in the change of resistance correspondingly. According to the Resistance-Voltage relation V=I*R. Here ‘V’ is the voltage drop, ‘R’ is the resistance of the sensor and ‘I’ is the current through it. By this relation as resistance changes the voltage drop across the sensor also change. This voltage is measured and is given to the circuit for further processes. The voltage range for using metal oxide sensor in from 200˚C to 400˚C. The working principle of polymer sensor is same as that of metal oxide sensor The only change is in the temperature range i.e., the room temperature.
Piezoelectric sensors are sub-divided into quartz crystal microbalances and surface acoustic wave. In quartz crystal the surface absorbs the gas molecules. This results in the change of mass, which causes a change in the resonant frequency of the quartz crystal. This change in frequency is proportional to the concentration of the test material. The change in frequency also results a change in the phase. In surface acoustic wave we measure the change in phase of the resonant frequency.
Calorimetric sensors are preferable only for combustible species of test materials. Here the sensors measure the concentration of combustibles species by detecting the temperature rise resulting from the oxidation process on a catalytic element.

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http://studentbank.in/report-ppt-on-e-no...n=lastpost


http://studentbank.in/report-electronic-...ars-report

http://studentbank.in/report-electronic-...ull-report

http://studentbank.in/report-electronic-...ars-report

http://studentbank.in/report-electronic-...ort?page=2

http://studentbank.in/report-electronic-...port--8224