The core component of a passive infrared detector is a pyroelectric sensor. Its main body is a thin-film ferroelectric material. This material is polarized under the action of an external electric field. When the external electric field is removed, it remains polarized, which is called spontaneous polarization. The spontaneous polarization has a Curie point temperature and temperature. At the Curie point temperature, a pyroelectric sensor is manufactured based on the relationship between polarization intensity and temperature. When a certain intensity of infrared radiation is applied to a polarized ferroelectric material, the temperature of the thin skin increases, the polarization intensity decreases, and the surface polarization charge decreases. This part of the charge is converted into an output voltage by the amplifier. If the radiation of the same intensity continues to irradiate, the temperature of the ferroelectric material stabilizes at a certain point and no longer discharges electric charge, that is, no voltage is output. Because the pyroelectric sensor only has voltage signal output during the temperature rise and fall, the optical system of the passive infrared detector must not only have the ability to condense infrared radiation, but also allow the heat condensed on the pyroelectric sensor to rise and fall. To ensure that the passive infrared detector has a voltage signal output when someone intrudes. In the digital passive infrared detector, the weak electrical signal output by the pyroelectric sensor is directly input to a powerful microprocessor, and all signal conversion, amplification, and filtering are performed in a processing chip, thereby improving the passive infrared. Detector reliability. At present, most of them use infrared plastic lens and Fresnel lens with multilayer beam structure. This lens is made of special plastic at one time, and several small lenses are arranged on a curved lens. The alert range is multiple single-beam states in different directions, forming a stereo alert in a stereo sector. Fresnel lenses are divided into several rows from top to bottom, with small lenses on the top and fewer on the bottom. That's because the upper part of the human body has strong infrared radiation, and the lower part has weak infrared radiation. In addition, it is also to prevent infrared radiation interference from small animals on the ground. 误报。 Infrared light has a poor penetrating power, and there should be no tall objects in the protection area, otherwise people in the shadow area will not be able to report the alarm. Do not face the place where there is a sudden cold or heat, or do not face the place where there is a light source, otherwise the changing hot air flow Will cause false alarms by infrared detectors .