The pyroelectric detector is constructed so that the sensitive element is cut into thin slices. After grinding into a very thin sheet of 5-50 μm, the two surfaces of the element are made into electrodes, similar to the structure of the capacitor. In order to ensure the absorption of crystals on the infrared, sometimes with black crystals or in the transparent electrode surface coated with a black film. When the infrared light is irradiated onto the already polarized ferroelectric sheet, the temperature of the sheet is raised so that its polarization intensity (charge per unit area) is reduced and the charge on the surface is reduced, which is equivalent to releasing a part of the charge Called pyroelectric sensor.

The released charge can be converted to an output voltage by an amplifier. If the infrared light continues to illuminate, so that the temperature of the ferroelectric sheet to a new equilibrium value, the surface charge will reach a new equilibrium concentration, no longer release the charge, there is no longer the output signal. This is different from other optoelectronic or thermal detectors, these detectors will be exposed to a certain response time to reach another stable state, then the maximum output signal. In contrast to the pyroelectric detector, in the steady state, the output signal drops to zero, and only the output signal is present during the rise and fall of the sheet temperature. Pyroelectric sensors are commonly used in the field of human infrared sensor to achieve automatic light switch, automatic tap switch, automatic door switches and other fields.