ABSTRACT
A chemical gas sensor can be de™ned as a device, which upon exposure to a gaseous species or molecules, alters one or more of its physical properties, such as mass, electrical conductivity, or dielectric properties, in a way that is possible to measure and quantify. These changes deliver an electrical signal, with a magnitude that is proportional to the concentration of the gas under test, which is measured as a quantity of the gas to which the measuring sensor is exposed. These changes, in some cases, may be spontaneous or they could be a slow response taking several minutes or more. The device should also show a reverse property after the gas has been removed. This reversal may take several minutes to hours depending on the nature of material and the gas involved. However, in certain cases, this reversal may not take place. The former case is ideal for gas-sensing applications. At present, many techniques are used for the purpose of gas detection and each technique has certain advantages and disadvantages as well. Depending on the nature of material, each sensor is known to be sensitive to a group of a family of gases and similarly each gas can be detected by different materials.
