A semiconductor gas sensor is a device that detects the presence or concentration of specific gases by utilizing the changes in the electrical properties of a semiconductor material when it comes into contact with the gas. These sensors are widely used in environmental monitoring, industrial safety, and home automation systems due to their high sensitivity and cost-effectiveness.
Semiconductor gas sensors can be broadly categorized into two types: resistive and non-resistive. Resistive sensors rely on the change in resistance of the semiconductor material when exposed to certain gases. Common materials used include tin oxide (SnOâ‚‚), manganese oxide (MnOâ‚‚), and other metal oxides. When these materials come into contact with flammable gases such as hydrogen, carbon monoxide, or hydrocarbons like methane, ethane, and benzene, a chemical reaction occurs, which leads to a change in the material's electrical resistance.
This change in resistance is directly related to the gas concentration and can be measured to determine the presence and level of the gas. For instance, when the gas concentration increases, the resistance of the sensor typically rises significantly, often following a linear relationship within a specific range. This makes it possible to convert the gas composition and concentration into an electrical signal for real-time monitoring and alarm systems.
Figure 4.42 illustrates the resistance-density relationship of a typical gas sensor. As shown, the sensor exhibits different levels of sensitivity to various gases—such as acetic acid, ethylene glycol, and hydrogen—while showing lower sensitivity to methane. Understanding this behavior is crucial for selecting the appropriate sensor for a given application.
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