18-09-2012, 11:50 AM
Electronic Nose Sensor Response and Qualitative Review of E-Nose Sensors
[attachment=33931]
Abstract
This paper presents the generalized response of
electronic nose sensors to odorant and reviews the range of
sensors used in electronic nose (e-nose) systems. The response of
the sensor is analyzed as first order time response.This paper
outlines the operating principles and important features of each
sensor type as well as the applications in which the different
sensors have been utilized. It also outlines the advantages and
disadvantages of each sensor for application in a cost-effective enose
system.
INTRODUCTION
An electronic nose is an instrument which comprises an array
of electronic chemical sensors with partial electivity and an
appropriate pattern recognition system, capable of
recognizing simple and complex odors.
All chemical sensors comprise appropriate, chemically
sensitive materials that are interfaced to a transducer.
Interaction of the analyte molecules with the chemically
sensitive material generates some physical changes that are
sensed by the transducer and converted to an output signal.
The range of gas sensing materials is potentially very broad
and can be divided into a number of ways, either by material
type or by the nature of the interaction with the analyte
(Gardner and Bartlett 1999) (Table 1)[1]. These interactions
are dependent on the shapes and the charge distributions
within the analyte molecules and the sensor materials, and are
similar to the interactions operative in the biological system
between the odorants and the receptor proteins. The types of
odor sensors that can be used in an e-nose need to respond to
odorous molecules in the gas phase.
SENSOR RESPONSE
The response of e-nose sensors to odorants is generally
regarded as a first order time response. The first stage in
odor analysis is to flush a reference gas through the sensor to
obtain a baseline. The sensor is exposed to the odorant,
which causes changes in its output signal until the sensor
reaches steady-state. The odorant is finally flushed out of the
sensor using the reference gas and the sensor returns back to
its baseline as shown in Figure-1.
The time during which the sensor is exposed to the odorant
is referred to as the response time while the time it takes the
sensor to return to its baseline resistance is called the
recovery time. The next stage in analyzing the odor is sensor
response manipulation with respect to the baseline. This
process compensates for noise, drift and also for inherently
large or small signals (Pearce et al., 2003)[8]. The three most
commonly used methods as defined by Pearce et al.
Comparison of MPEN with other electronic noses:
Other conventional gas sensing devices have employed
methods based on polymer, metal oxide, infrared
technologies etc. These types of sensor tend to be very
application specific, wear out within short periods, require
frequent calibration procedures and are often relatively
expensive to produce. Most of these sensors have to be
designed, manufactured and calibrated to detect one
particular known gas or particular odor. MPEN is relatively
low cost and can last months or years if required. MPEN is
virtually calibrated, trained and adapted to all possible
applications by software procedures so that it can detect one
expected gas, a range of gases, or analyze a sample of an
unknown gas or gases depending on the end user needs.
CONCLUSION
A wide variety of e-nose sensors including conducting
polymer composite, intrinsically conducting polymer and
metal oxide conductivity gas sensors, SAW and QCM
piezoelectric gas sensors, optical gas sensors and MOSFET
gas sensors have been reviewed in this paper. These systems
offer excellent discrimination and lead the way for a new
generation of ―smart sensors‖ which may mould the future
commercial applications of gas sensors. The principle of
operation, advantages, disadvantages and applications of
each sensor type in e-nose systems have been clearly
outlined and a summary of this information is given (Table-
2).
[attachment=33931]
Abstract
This paper presents the generalized response of
electronic nose sensors to odorant and reviews the range of
sensors used in electronic nose (e-nose) systems. The response of
the sensor is analyzed as first order time response.This paper
outlines the operating principles and important features of each
sensor type as well as the applications in which the different
sensors have been utilized. It also outlines the advantages and
disadvantages of each sensor for application in a cost-effective enose
system.
INTRODUCTION
An electronic nose is an instrument which comprises an array
of electronic chemical sensors with partial electivity and an
appropriate pattern recognition system, capable of
recognizing simple and complex odors.
All chemical sensors comprise appropriate, chemically
sensitive materials that are interfaced to a transducer.
Interaction of the analyte molecules with the chemically
sensitive material generates some physical changes that are
sensed by the transducer and converted to an output signal.
The range of gas sensing materials is potentially very broad
and can be divided into a number of ways, either by material
type or by the nature of the interaction with the analyte
(Gardner and Bartlett 1999) (Table 1)[1]. These interactions
are dependent on the shapes and the charge distributions
within the analyte molecules and the sensor materials, and are
similar to the interactions operative in the biological system
between the odorants and the receptor proteins. The types of
odor sensors that can be used in an e-nose need to respond to
odorous molecules in the gas phase.
SENSOR RESPONSE
The response of e-nose sensors to odorants is generally
regarded as a first order time response. The first stage in
odor analysis is to flush a reference gas through the sensor to
obtain a baseline. The sensor is exposed to the odorant,
which causes changes in its output signal until the sensor
reaches steady-state. The odorant is finally flushed out of the
sensor using the reference gas and the sensor returns back to
its baseline as shown in Figure-1.
The time during which the sensor is exposed to the odorant
is referred to as the response time while the time it takes the
sensor to return to its baseline resistance is called the
recovery time. The next stage in analyzing the odor is sensor
response manipulation with respect to the baseline. This
process compensates for noise, drift and also for inherently
large or small signals (Pearce et al., 2003)[8]. The three most
commonly used methods as defined by Pearce et al.
Comparison of MPEN with other electronic noses:
Other conventional gas sensing devices have employed
methods based on polymer, metal oxide, infrared
technologies etc. These types of sensor tend to be very
application specific, wear out within short periods, require
frequent calibration procedures and are often relatively
expensive to produce. Most of these sensors have to be
designed, manufactured and calibrated to detect one
particular known gas or particular odor. MPEN is relatively
low cost and can last months or years if required. MPEN is
virtually calibrated, trained and adapted to all possible
applications by software procedures so that it can detect one
expected gas, a range of gases, or analyze a sample of an
unknown gas or gases depending on the end user needs.
CONCLUSION
A wide variety of e-nose sensors including conducting
polymer composite, intrinsically conducting polymer and
metal oxide conductivity gas sensors, SAW and QCM
piezoelectric gas sensors, optical gas sensors and MOSFET
gas sensors have been reviewed in this paper. These systems
offer excellent discrimination and lead the way for a new
generation of ―smart sensors‖ which may mould the future
commercial applications of gas sensors. The principle of
operation, advantages, disadvantages and applications of
each sensor type in e-nose systems have been clearly
outlined and a summary of this information is given (Table-
2).