The document discusses gas sensors and how nanotechnology has influenced their development. It describes how gas sensors can detect harmful gases using various technologies like metal-oxide-semiconductor sensors. Nanotechnology has allowed these sensors to use nano-structured metal oxides, improving their speed, power needs, detection limits and ability to operate at lower temperatures in a more economical way. The document outlines the working principles and applications of gas sensors.
2. Introduction
๏ต A gas sensor is a device that detects the presence of gases in an area, often as part of a safety
system.
๏ต This type of device is important because there are many gases that can be harmful to organic
life, such as humans or animals.
๏ต It can be used to detect combustible, flammable and toxic gases, and oxygen depletion.( Gases:
CO, Nox ,Sox ,CO2 ,NH4 ,CH4 ..etc,.)
๏ต Common sensors includes:
1. Combustible gas sensors,
2. photoionization detectors,
3. infrared point sensors,
4. ultrasonic sensors,
5. Electrochemical gas sensors, and
6. metal-oxide-semiconductor sensors (MOS sensors).
3. ๏ต Influence of nanotechnology is mostly seen in nano-structured metal
oxide semiconductors(MOSโs)
๏ต These are mostly N-type Semiconductors.
๏ต They can operate around 300-600ยฐC.
๏ต MOS Gas sensors contains two segments of instrumentations
1. Sensing film.
2. Miniature heater elements.
CLASSIFICATION OF SENSORS
GAS SENSORS
Detection mechanism Materials used
(voltage, adsorption, (MOSโs ,pt & pd, oxide film thickness,
Absorption, current.,etc,.) grain size ,porosity, material sintering temperature and time )
4. WORKING PRINCIPLE :
They work on the basic principles such as
Adsorption, Desorption, Absorption, Evaporation,etc,.
5.
6.
7. โข In clean air, donor electrons in tin dioxide are attracted toward oxygen which is adsorbed on
the surface of the sensing material, preventing electric current flow.
โข In the presence of reducing gases, the surface density of adsorbed oxygen decreases as it
reacts with the reducing gases. Electrons are then released into the tin dioxide, allowing
current to flow freely through the sensor. The current flow will give the equivalent readings
of the measured gas.
9. ADVANTAGES OF USING NANO SIZED GAS SENSORS ELEMENTS:
๏ต Potentially faster
๏ต Requires low power
๏ต Comes with lower limit of detection
๏ต Operates even at low temperatures
๏ต More heat shock resistant
๏ต Economically low in cost
APPLICATIONS:
๏ต Analysis of organic vapours
๏ต Breath analysis for traffic safety
๏ต Disease diagnosis
๏ต Testing smell ,taste of food ,perfumes etc
