What is a sensor?

Sensors can be classified from different angles: their conversion principle (the basic physical or chemical effect of sensor work); Their uses; Their output signal types, materials and processes for manufacturing them, etc. According to the working principle of sensors, they can be divided into physical sensors and chemical sensors. Classification of sensor working principle Physical sensors apply physical effects, such as piezoelectric effect, magnetostrictive phenomenon, ionization, polarization, thermoelectric, photoelectric, magnetoelectric and other effects. Small changes in the measured signal amount will be converted into electrical signals. Chemical sensors include sensors with chemical adsorption, electrochemical reaction and other phenomena as causal relations, and small changes in the measured signal amount will also be converted into electrical signals. Some sensors can neither be classified as physical sensors nor as chemical sensors. Most sensors work according to physical principles. Chemical sensors have many technical problems, such as reliability, possibility of mass production, price and so on. After solving these problems, the application of chemical sensors will greatly increase. The following table lists the application fields and working principles of common sensors.

1. Sensors are classified according to their uses:

Pressure sensor and force sensor position sensor liquid level sensor energy consumption sensor speed sensor acceleration sensor radiation sensor thermal sensor 24GHz radar sensor.

2. Sensors are classified according to their principles:

Vibration sensor, humidity sensor, magnetic sensor, gas sensor, vacuum sensor, biosensor, etc.

3. Sensors are classified according to their output signals:

Analog sensor-converts measured non-electric quantity into analog electric signal. Digital sensor-converts the measured non-electric quantity into digital output signal (including direct and indirect conversion). Pseudo-digital sensor-converts the measured signal into frequency signal or short-period signal for output (including direct or indirect conversion). Switch sensor-When the measured signal reaches a certain threshold, the sensor outputs a set low-level or high-level signal accordingly.

4. Sensors are classified according to their materials:

Under the influence of external factors, all substances will make corresponding and characteristic reactions. Among them, those materials that are most sensitive to external effects, that is, materials with functional characteristics, are used to make sensitive elements of sensors. From the perspective of application materials, sensors can be divided into the following categories according to the types of materials used: (1) metal polymer ceramic mixture; (2) Conductor-insulator semiconductor magnetic materials are classified according to their physical properties; (3) the crystal structure of the material; The development of sensors is closely related to the adoption of new materials, which can be summarized into the following three directions: (1) Exploring new phenomena, effects and reactions in known materials, and then making them practical in sensor technology. (2) Explore new materials and apply those known phenomena, effects and reactions to improve sensor technology. (3) Explore new phenomena, new effects and new reactions on the basis of studying new materials, and realize them in sensor technology. The progress of modern sensor manufacturing industry depends on the development intensity of new materials and sensitive components used in sensor technology. The basic trend of sensor development is closely related to the application of semiconductors and dielectric materials. Table 1.2 gives some materials that can be used in sensor technology and can convert energy forms.

5. Sensors are classified according to their manufacturing process:

Integrated sensor thin film sensor thick film sensor ceramic sensor integrated sensor is manufactured by standard technology for producing silicon-based semiconductor integrated circuits. Usually, some circuits used for preliminary processing of measurement signals are also integrated on the same chip. The thin film sensor is formed by a thin film of a corresponding sensitive material deposited on a dielectric substrate (substrate). When a hybrid process is used, a part of the circuit can also be fabricated on the substrate. Thick-film sensor is made by coating the slurry of the corresponding material on a ceramic substrate usually made of Al2O3, and then heat-treating it to form a thick film. Ceramic sensors are produced by standard ceramic technology or some variant technologies (sol-gel, etc.). ). After the proper preparation operation is completed, the molded parts are sintered at high temperature. There are many similarities between thick film technology and ceramic sensor technology. In some aspects, thick film technology can be considered as a variant of ceramic technology. Each technology has its own advantages and disadvantages. Due to the low investment in R&D and production and the high stability of sensor parameters, it is more reasonable to use ceramic and thick film sensors.