Any object higher than the absolute temperature will produce electromagnetic radiation-infrared. However, the wavelength and energy of the infrared radiated by objects of different temperatures are different. The higher the surface temperature of an object, the stronger its radiant energy. Most of the infrared radiation produced by the human body is in the 7-14um band, and its peak wavelength is about 9.4um.
From the above analysis, it can be seen that as long as there are people within a certain distance, the sensor can respond accordingly. This is exactly the purpose of the anti-theft system, which is to detect the intrusion of "bad guys" into the guard area. Anything above absolute zero can radiate infrared rays.
Based on the above reasons, when designing the condenser lens, the smooth optical mirror surface is often prismatic or columnar, so that the monitored space produces a series of alternating narrow infrared "high sensitivity sensitive areas" and "blind areas". When someone is walking in front of the mirror, the infrared rays emitted by the human body will continuously enter the "blind area" from the "highly sensitive area", and the infrared rays transmitted to the passive infrared sensor will sometimes disappear. That is, a large number of light pulses enter the infrared detection element, and after conversion, they output correspondingly changed electrical pulses, thereby improving its receiving sensitivity and increasing its detection range. This kind of optical system that can improve the detection range and accuracy is called Fresnel Er lens.
Passive motion sensor, when detecting human body radiation, the output pulse signal is only an alternating signal in the range of 0.3-10} lZ of tens of UV. Since the signal is extremely weak, it must be filtered and amplified before it can be received by the post instrument.