The Fresnel lens is by the French physicist augustine Augustin Fresnel. The Fresnel (j), he invented in 1822 first use this lens design are used to establish the Fresnel lens system - a glass lighthouse lens.

       The Fresnel lens  is a kind of micro-structure of optical element, look from the front its like a dart dish, by a ring a part of concentric garden composition. 

      The Fresnel lens in heat release the role of an infrared have two: one is focusing role, will soon heat release infrared signal reflection refraction (in), the second function is on PIR will detect area is divided into several Ming area and dark area, make into the moving object detection area to temperature changes in the form of heat release on PIR changes infrared signal.