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. 

The Fresnel lens, simply say to be in the lens side have equi-distant tooth tattoo. Through these tooth tattoo, can achieve to specified spectrum light band tong (reflecting or refraction) role. The traditional grinding optical equipment band-pass optical filters are expensive. The Fresnel lens can greatly reduce costs. A typical example is PIR (passive infrared detector). PIR used widely in alarm. If you take a look, you will find in each PIR on all have a plastic little hat. This is the Fresnel lens. Little hat internal are engraved the tooth tattoo. This kind of Fresnel lens can be incident light frequency peak limited to 10 micron around (human infrared ray radiation peak).

Pyroelectric infrared sensor is mainly composed of a kind of tall thermoelectric coefficients of materials, such as zirconium lead titanate department ceramics, litao3, acid three made gedaliah titanium size for 2 * 1mm detection devices. In each detector loaded within one or two detection devices, and two detection with the polar components in series and to suppress because of its own temperature rise of interference. By detecting components will explore and receive the infrared radiation into a glimmer of voltage signal, the outfit is in probe inside the mosfet enlargement outward output. In order to improve the detection sensitivity in order to increase the probe detecting distance, be in commonly the probe ahead furnish a Fresnel lens, using the Fresnel lens special optical principle, the probe ahead produce a variations of the "blind" and "high sensitive area", in order to improve its detection rx sensitivity. When someone from the lens body before walked out of the infrared ray continually alternate from "blind" enter "high sensitive area", this makes receives the infrared signal to suddenly suddenly weak pulse form strong input, thus strong its energy prices.

The Fresnel lens and amplifying circuit suitably, but will amplification 70 decibels, such pyroelectric infrared sensor can be detected 10 ~ 40 meters geographical area action.

Human radiation wavelengths of infrared center for 9 ~ 10 -- um, but detection components in the wavelength of sensitivity 0.2 ~ 20 - um range almost constant. The sensor has opened a top equipped with filter slice window, the filter can through light wavelength range for 7 ~ 10 -- um, and it fits in the human body infrared radiation detection, and for other wavelength of infrared by filter to absorb so that they formed a special used to detect human radiation infrared sensors.

nfrared sensor IC is a kind of with fairly good performance of the sensor signal processing integrated circuits. It matchs with pyroelectric infrared sensors and a few external components constitute a passive pyroelectric infrared switch. Can automatically rapid opening all kinds of incandescent lamp, fluorescent lamp, buzzer, automatic, electric fan, dryer and automatic device such as wash one's hands, especially suitable for enterprises, hotels, stores, warehouse and family of corridor and other sensitive area, or for safe area of automatic lighting, lighting and alarm systems.