Principle of Fresnel lens

　　Fresnel lens is made according to Fresnel principle, which divides infrared ray into visible area and blind area. At the same time, it has the function of focusing, which greatly increases the sensitivity of pyroelectric human infrared sensor (PIR). Fresnel lens has two forms: refractive and reflective. One is focusing, which refracts (reflects) the pyrolytic infrared signal on the PIR; The second is to divide the detection area into several bright areas and dark areas, so that moving objects entering the detection area can generate variable pyroelectric infrared signals on the PIR in the form of temperature changes, so that PIR can generate variable electrical signals.

　　Under static conditions, there is infrared light in the space. Because the dual probe adopts complementary technology, it will not produce electrical signal output. Under dynamic conditions, the human body is induced by source A or source B successively when passing through the probe, and the dual sources lose their complementary balance role and generate signal output sensitively. When people move vertically towards the probe, the dual sources are difficult to generate signal output, so it is appropriate to install the detector parallel to the walking direction of people.

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Diameter 3mm size