The Fresnel Lens was invented by the French physicist Augustin Fresnel. He originally used this Lens design in 1822 to build a glass Fresnel Lens system-a lighthouse Lens.
Fresnel Lens is an optical element with a fine structure. Viewed from the front, it looks like a dartboard, consisting of a ring of concentric circles.
The Fresnel Lens has two functions in pyro-infrared sensing: One function is focusing. That is, the pyro-infrared signal is refracted (reflected) on the PIR. The other function is to divide the detection area into a number of bright and dark areas, so that moving objects entering the detection area can produce a changing pyro-infrared signal on the PIR in the form of temperature changes.
The Fresnel Lens, in simple terms, has equidistant teeth on one side of the lens. Through these teeth, the optical bandpass (reflection or refraction) of the specified spectral range can be achieved. Bandpass optical filters for traditional polished optical equipment are expensive to manufacture. Fresnel Lens can greatly reduce costs. A typical example is PIR (Passive Infrared Detector). PIR is widely used in alarms. If you take one and take a look, you will find that there is a small plastic cap on each PIR. This is the Fresnel Lens. The inside of the little hat is carved with teeth. This Fresnel Lens can limit the frequency peak of incident light to about 10 microns (the peak of infrared radiation from the human body).