30-11-2012, 04:51 PM
ELECTRONIC Noses (EN)
[attachment=41945]
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.
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.
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.
[attachment=41945]
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.
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.
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.