Infrared is absorbed by the object will be converted into heat. The thermal detector utilizes the thermal effect of infrared radiation. When the infrared sensor of the thermal probe device absorbs infrared radiation, it will cause the temperature to rise and change the relevant physical parameters of the sensitive element. The infrared radiation absorbed by the detector can be determined by measuring these physical parameters and their changes.

The main advantages of the thermal detector are: response band wide, the response range for the entire infrared area, work at room temperature, easy to use. There are four main types of thermal detectors: thermistor type, thermal resistance type, high Lai pneumatic type and pyroelectric type. In these four types of detectors, pyroelectric detector detection efficiency is highest, the frequency response is the widest, so this sensor is developing faster, the application of a Fan 1 Wai is also the most extensive.

In the case of an applied electric field, the charged particles (electrons, nuclei, etc.) in the dielectric will be subjected to the effect of the electric field force. In general, the positive charge tends to the cathode and the negative charge tends to the anode. As a result, one surface of the dielectric is positively charged , The relative surface with a negative, this phenomenon is called the dielectric "electrode". For most dielectrics, the polarization state disappears after the voltage is removed, but there is a type of dielectric called "ferroelectric" that remains polarized after the applied voltage is removed.

In general, the polarization strength Ps (charge per unit area) of the ferroelectrics is related to temperature, and the temperature increases and the polarization intensity decreases. The temperature rises to a certain extent, the polarization will suddenly disappear, the temperature is called the Curie point, below the Curie point, the polarization intensity Ps is a function of temperature, the use of this relationship made of thermal detectors For pyroelectric detector.