Discuss the principle of operation of a gas sensor.

Gas sensors function by detecting changes in physical properties resulting from the interaction between target gas molecules and a sensing material. This interaction can manifest through chemical reactions, absorption/desorption processes, electrochemical reactions, optical absorption, or the piezoelectric effect. For example, metal oxide gas sensors rely on the change in conductivity when the target gas reacts with the metal oxide surface, while electrochemical gas sensors generate measurable electrical signals proportional to the gas concentration through electrochemical reactions with an electrolyte. Optical gas sensors, such as infrared sensors, detect gas concentrations by measuring the absorption of specific wavelengths of light by the target gas molecules. These principles enable gas sensors to play a crucial role in monitoring air quality, detecting hazardous gases, and ensuring safety across a wide range of industrial, environmental, and domestic applications.