Chemical sensors are used for chemical measurements and are commonly used in production process analysis and environmental pollution monitoring. They also have important applications in mineral resource exploration, meteorological observation and telemetry, industrial automation, remote diagnosis and real-time monitoring in medicine, fresh food preservation and fish detection in agriculture, theft prevention, security alarms and energy conservation.
What are the classifications of chemical sensors?
Classification by sensing method: Based on the sensing method, chemical sensors can be divided into contact chemical sensors and non-contact chemical sensors.
There are two structural forms of chemical sensors: one is the discrete sensor, such as an ion sensor, where the liquid or solid membrane functions as a receiver, and the membrane performs the electrical signal conversion function. The receiving and conversion parts are separate, which is beneficial for optimizing each function individually; the other is the integrated sensor, such as a semiconductor gas sensor, where the molecule trapping function and the current conversion function occur in the same part, which is beneficial for the miniaturization of chemical sensors.
Classification by Detection Object: Based on the detection object, chemical sensors are classified into gas sensors, humidity sensors, ion sensors, and biosensors.
1. Gas Sensors: Sensing elements are mostly oxide semiconductors, sometimes with trace amounts of noble metals added as sensitizers to enhance their activation of gases. For electron-donating reducing gases such as hydrogen, carbon monoxide, and hydrocarbons, N-type semiconductors are used; for electron-accepting oxidizing gases such as oxygen, P-type semiconductors are used. The semiconductor is fixed in a film form on an insulating substrate or porous sintered body to form the sensing element. Gas sensors are further classified into semiconductor gas sensors, solid electrolyte gas sensors, contact combustion gas sensors, crystal oscillator gas sensors, and electrochemical gas sensors.
2. Humidity sensor: This is a sensor that measures the water vapor content in the environment. It is further divided into electrolyte type, polymer type, ceramic type and semiconductor type humidity sensor.
3. Ion Sensor: This is an ion-selective electrode that exhibits a selective response to ions. It is based on the membrane potential generated by the membrane's selective response to ions. The sensing membrane of an ion sensor can be a glass membrane, a liquid membrane containing dissolved active substances, or a polymer membrane, with polyvinyl chloride (PVC) membranes being the most commonly used.
4. Biosensors: These are instruments that are sensitive to biological substances and convert their concentration into electrical signals for detection. A key advantage of biosensors is their ability to select biological substances based on their molecular structure.
