1. Fatemeh Bagheri Under supervision of Dr. Haratidadeh
Gas Sensors
Fatemeh Bagheri
Under supervision of Dr. Haratidadeh

2. Contents
Introduction
History
Application
Gas Sensing Method 1 2 4 3

3. 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.
صفحه 33 م ب
1927 Dr. Oliver W. Johnson invented the first catalytic combustion gas sensor leading to the first combustible gas Indicator

4. 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.

5. 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.

6. Indicators of the Performance of Gas sensors
Title
selectivity
sensitivity
response time
reversibility
energy consumption
fabrication cost

7. 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)
 از موادی که با گاز خود آلوده کننده هستند اجتناب شود. حلال پایه رنگ و روغن، چسب ها، قالی، براده چوب و بسیاری از دیگر مصالح و فرآورده های ساختمانی، فرمالدئید و ترکیبات فرار ارگانیک VOC آزاد می کنند.

8. Application

9. Application

10. 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)
 از موادی که با گاز خود آلوده کننده هستند اجتناب شود. حلال پایه رنگ و روغن، چسب ها، قالی، براده چوب و بسیاری از دیگر مصالح و فرآورده های ساختمانی، فرمالدئید و ترکیبات فرار ارگانیک VOC آزاد می کنند.

11. 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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12. 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.

13. 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.
حسگر شیمیایی(نت)
Conducting polymer sensors

14. 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

15. 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.

16. 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
حسگر شیمیایی

17. 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.

18. 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%.

19. 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.
رطوبت سنج ها برای کنترل هوای سالن ها، اتاق های تمیز (clean room)، سالن های گل خانه، استخرها و سالن های ورزشی کاربرد دارد. سنسور های رطوبت قادر به تشخیص رطوبت هوا و نمایش آن به صورت درصد (رطوبت 0 تا 100%) می باشد. 

20. 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.

21. Optical Methods photoacoustic spectroscopy:
انتشار صوت توسط ماده به علت جذب نور
وقتی به یک گاز خاص نور تابانده میشود مقداری از انرژی نور توسط گاز جذب میشود . مقدار انرژی که جذب میشود به غلظت گاز بستگی دارد.
این انرژی جذب شده فورا تبدیل به حرارت میشود و باعث بالا رفتن فشار خواهد بود.

22. Calorimetric Methods
Pellistors constitute a major class of electrical gas sensors.
Specifically, pellistors can be divided in two types: Catalytic and Thermal Conductivity. .
نقش کاتالیست در فرآیند آشکارسازی گاز را می توان در عناوین زیر خلاصه کرد:
1. باعث بالارفتن سرعت واکنش گاز هدف با لایه فعال می شود - در نتیجه زمان پاسخ سنسور به حدود چند ثانیه کاهش میآبد.
2. باعث انتخاب پذیری واکنش میشود - کاتالیست نقش فیلتر را بازی میکند. بدین معنی که تنها دسته ی خاصی از گازها (یا تنها یک نوع گاز) با سنسور واکنش صورت دهد.

23. 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.

25. 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 . When you open the photo, a wave of aroma--your Mom's cooking--fills the air

26. Reference
“A Survey on Gas Sensing Technology”, journal/Sensors 2012, 12, ; doi: /s
“A review of gas sensors employed in electronic nose applications”, Sensor Review, Volume 24 Number pp
Peter Hauptmann, “sensors principles and applications”
“Chemical Sensors for Electronic Nose Systems”, Microchim. Acta 149, 1–17 (2005)

27. Thanks