20-01-2011, 05:05 PM
[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.
