There are two type for fresnel lens, flat and round. The main material for fresnle lens is poly methyl methacrylate. Fresnel lens ultrathin structure, large size and arbitrary shape cutting, excellent light transmittance of traditional geometric convex lens has many advantages, its weight less than convex lens and a variety of occasions. The fresnel lens is a optical element, one side is smooth, another side is by a ring a part of concentric garden composition. Fresnel lens arrays designed for Passive Infrared Sensor. The optical surface increases lens sensitivity for PIR sensor application. All the PIR sensor must work with the Fresnel Lens.