Gas Sensors

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Gas Sensors

• Fatemeh Bagheri
• Under supervision of Dr. Haratidadeh

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Contents
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History
Gas leak detection methods became a concern after
the effects of harmful gases on human health were
discovered. Before modern electronic sensors,
early detection methods relied on less precise
detectors. Through the 19th and early 20th
centuries, coal miners would bring canaries down
to the tunnels with them as an early detection
system against life-threatening gases.
1927 Dr. Oliver W. Johnson invented the first
catalytic combustion gas sensor leading to the
first combustible gas Indicator
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Introduction

• A gas sensor (or gas detector) is a device that
  detects the presence of gasses in an area.
• A sensor is a technological device that detects /
  senses a signal, physical condition and chemical
  compounds.
• They are manufactured as portable or stationary
  (fixed) units and work by signifying high levels
  of gases through a series of audible or visible
  indicators, such as alarms, lights or a
  combination of signals.

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Gas Sensor
During the last fifty years, different studies
have established various branches of gas sensing
technology. Among them, the three major areas
that receive the most attention are investigation
of different kinds of sensors, research about
sensing principles, and fabrication techniques.
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Indicators of the Performance of Gas sensors
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Application

• industrial production (e.g.,methane detection in
  mines)
• automotive industry (e.g., detection of polluting
  gases from vehicles)
• (3) medical applications (e.g., electronic noses
  simulating the human olfactory system)
• (4) indoor air quality supervision (e.g.,
  detection of carbon monoxide)
• (5) environmental studies (e.g., greenhouse gas
  monitoring)

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Application
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Application
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Application

• industrial production (e.g.,methane detection in
  mines)
• automotive industry (e.g., detection of polluting
  gases from vehicles)
• (3) medical applications (e.g., electronic noses
  simulating the human olfactory system)
• (4) indoor air quality supervision (e.g.,
  detection of carbon monoxide)
• (5) environmental studies (e.g., greenhouse gas
  monitoring)

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Metal Oxide Semicondcutor

• The most common sensing materials are metal oxide
  semiconductors, which provide sensors with
  several advantages such as low cost and high
  sensitivity.
• Sensors based on metal oxide semiconductors are
  mainly applied to detect target gases through
  redox reactions between the target gases and the
  oxide surface.
• The resistance variation could be detected by
  measuring the change of capacitance, work
  function, mass, optical characteristics or
  reaction energy.
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Metal Oxide Semiconductor

• Metal oxides, such as SnO2, CuO, Cr2O3, V2O5, WO3
  and TiO2, can be utilized to detect combustible,
  reducing, or oxidizing gases with sensors which
  are mainly based on the resistance change
  responses to the target gases.
• Among all sensors based on metal oxide
  semiconductors, the sensitivity of SnO2-based
  ones is relatively high, leading to its greater
  popularity.

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Polymers

• Generally, sensors based on metal oxide
  semiconductors exhibit significantly greater
  sensitivity to inorganic gases like ammonia and a
  few kinds of volatile organic compounds (VOCs)
  like alcohol (C2H5OH) and formaldehyde. however,
  some other VOCs which could cause adverse health
  effects when their concentration over a certain
  threshold cannot be detected by metal oxide
  semiconductor-based sensors.
• polymers used for gas sensing can be further
  classified into two groups
• conducting polymers
• non-conducting polymers.

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Polymers

• conducting polymers
• it is well established that the electrical
  conductivity of these conducting polymers is
  affected through exposure to diverse organic and
  inorganic gases.
• Conducting polymers that can be used as gas
  sensing materials include polypyrrole (PPy),
  polyaniline (PAni), polythiophene (PTh) and their
  derivatives

Each polymer changes its size, and therefore its
resistance, by a different amount, making a
pattern of the change
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Polymers

• Non-Conducting Polymers Non-conducting polymers
  have been widely utilized as sorptive coatings on
  different sensor devices.
• Polymers with different properties or
  physisorption mechanisms can be coated onto
  respective transducers. For instance, polymer
  layers causing changes in resonance frequency,
  dielectric constant and enthalpy upon
  absorption/desorption of analytes can be
  respectively coated on mass-sensitive.g. (Quartz
  Crystal Microbalance (QCM), Surface Acoustic Wave
  (SAW) and SurfaceTransverse Wave (STW),
  capacitive (dielectric) and calorimetric sensor
  devices.

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• Polymer-based gas sensors have advantages such
  as
• high sensitivities
• short response times
• operate at room temperature
• low cost of fabrication
• simple and portable structures
• dissolving the polymers into the solution in a
  uniform way

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Carbon nanotubes

• Conventional sensing materials like metal oxide
  semiconductors have to deal with the problem of
  poor sensitivity at room temperature, while
  carbon nanotubes (CNTs) attract more attention
  because of their unique properties and have
  become the most promising materials for
  high-sensitive gas sensors.
• As a kind of promising sensing material, CNTs,
  have been found to possess electrical properties
  and are highly sensitive to extremely small
  quantities of gases, such as alcohol, ammonia
  (NH3), carbon dioxide (CO2) and nitrogen oxide
  (NOx) at room temperature, while other materials
  like metal oxides have to be heated by an
  additional heater in order to operate normally.
• When utilized as sensing materials, on the one
  hand, CNTs are often decorated with other
  materials in order to enhance their sensitivity
  and selectivity.

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Carbon nanotubes

• SWCNTs have been employed in RFID tag antennas
  for toxic gas sensing, in which the backscattered
  power from the tag antenna would be easily
  detected by the RFID reader if the concentration
  of ammonia rises to 4.

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Moisture Absorbing Material
sensors like that could be located inside walls
or floors of buildings, mainly in order to
prevent costly damage due to mold or decay and it
could also be positioned under hidden water pipes
for detection of leakage. Other applications
detecting humidity levels, like water vapor
concentration monitoring for food storage, could
also utilize methods like those based on moisture
absorbing materials and RFID tags.
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Optical Methods
Optical methods for gas sensing are mostly based
on spectroscopy. Only a few commercial gas
sensors are based on optical principles.
Spectroscopic analysis mainly involves techniques
based on absorption and emission
spectrometry. there are many types of improved
absorption spectrometry including
Differential Optical Absorption Spectroscopy
(DOAS), Tunable Diode Laser Absorption
Spectroscopy (TDLAS), Raman Light Detection and
Ranging (LIDAL), Differential Absorption LIDAR
(DIAL), Intra-Cavity Absorption Spectrometry
(ICAS), etc. Due to the mentioned factors, these
techniques are more commonly applied to gas
detectors, which allow for more complicated
system design and higher cost to gain excellent
sensitivity, selectivity and reliability, than
gas sensors.
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Optical Methods
photoacoustic spectroscopy
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Calorimetric Methods

• Pellistors constitute a major class of electrical
  gas sensors.
• Specifically, pellistors can be divided in two
  types Catalytic and Thermal Conductivity.
• .

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Acoustic Methods

• Surface acoustic wave sensor SAWs can be excited
  on a piezoelectric crystal by the use of an
  inter-digitated transducer (IDT). The most common
  substrates for SAWs are ST-cut (stress
  temperaturecompensated) quartz or LiNbO3.

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Feature
Imagine being a thousand miles from home, and
your mother cooks your favorite meal for you.
Then she takes a photo of it and sends it by
e-mail. When you open the photo, a wave of
aroma--your Mom's cooking--fills the air
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Reference

• A Survey on Gas Sensing Technology,
  journal/Sensors 2012, 12, 9635-9665
  doi10.3390/s120709635
• https//www.citytech.com/loader/frame_loader.asp?p
  agehttps//www.citytech.com/technology/pellistors
  .asp
• http//sensors.blogfa.com/post-36.aspx
• A review of gas sensors employed in electronic
  nose applications, Sensor Review, Volume 24
  Number 2 2004 pp. 181-198
• http//en.wikipedia.org/wiki/Gas_detector
• http//www.chromedia.org/chromedia?waxtrappwlqdcD
  sHqnOxmOlIEcClBwFjEsubNavrwhpbjDsHqnOxmOlIEcClBw
  FjEQ
• Peter Hauptmann, sensors principles and
  applications
• http//www.figaro.co.jp/en/technicalinfo/principle
  /catalytic-type.html
• Chemical Sensors for Electronic Nose Systems,
  Microchim. Acta 149, 117 (2005)

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Thanks