The last section we introduced what is the Fresnel lens is, to this concept you should understand somewhat, the application of the place is very much also, here we introduce the function of Fresnel lens. Fresnel lens effect has two: one is the focus role, will release the infrared signal hot refractive index (albedo) in PIR, the second function is divided into many in sea will detect a Ming area and dark area, make into detection waters of the move objects can be to measure the change in the way the PIR changes heat release infrared signal. Fresnel lens, and easy to say is in the side of the lens of equidistance ridges. After the department ridges, able to reach for the general category named spectrum light waves (occurs or make refraction) role. The traditional grinding of bandpass optical equipment optical filter cost is high. Fresnel lens can greatly reduce ready cash. The typical example is PIR (active red insider detector). PIR broad used in radar. If you take a look, you will find that in each PIR have a plastic little hat. This is the Fresnel lens. Small caps are external engraved the ridges. The Fresnel lens can will incident light peak frequency to 10 silk m restricted internal and external (red inside the human body irradiation peak). Capital equal low. The Fresnel lens can through narrowband interference in the light of the filter focus of the probe silicon photoelectric level 2 photosensitive surface. By Fresnel lens organic glass into, ShiBuDe with any organic filtrate (such as ethanol, etc) to wipe. When the dust can use first alcoholize water or general water purification flush, again next cotton wool to wipe!