Application of Fresnel Lens in Passive Infrared Detection

　　The role of Fresnel lens in the whole passive infrared detector is that when someone enters the detection range, the Fresnel lens will focus the infrared light released by the human body through the lens to the same focus in the remote A area or the middle distance B area or the near distance C area (this focus is the design focus of the whole lens, and the distance from the focus to the lens is called the focal length). The focal point is the area accepted by the thermal sensor. The infrared light is just received by the thermal sensor. The thermal sensor converts the optical signal into an electrical signal and sends it to the electronic circuit to drive the load. The focal length of each layer of the multilayer Fresnel lens on the market is different, because its detection distance is different, and it can be adjusted according to the user's requirements during design, which can also be called the multi focal length Fresnel lens in practice.

　　Fresnel lens has the advantages of small size, economy and applicability, and has occupied the main market share in the security field. In addition to using Fresnel lens to design the optical system of infrared detector, parabolic reflector is also a common technology according to different application areas and requirements of the market. The advantages of aggregation can not be achieved by Fresnel lens in some aspects. The optical system composed of parabolic reflector has such outstanding characteristics as less heat energy absorption of the mirror body, small scattering loss, high efficiency, high imaging accuracy, long detection distance, etc., which is suitable for the use of passive infrared detectors with long distance and large range.

　　As the name implies, the parabolic reflector plays a reflective role in the optical system. Its working principle is that the light emitted from the outside is reflected and focused to a point through the reflector. The location of this focus is exactly the surface sensed by the thermoluminescence sensor. The infrared light is received by the thermoluminescence sensor. The thermoluminescence sensor converts the optical signal into an electrical signal and sends it to the electronic circuit to drive the load to work.

　　Reflectors can be used on detectors with different requirements. If classified functionally, they can be divided into wide-angle reflectors and curtain reflectors, which can be used on ceiling mounted and wall mounted infrared detectors. And it can be designed into multi-layer and multi view areas, which can detect far, medium and short distances, and the distance can reach 30 meters. The detection angle can be designed to be (0-120) degrees (see the following figure). The size of this angle should be set according to the size of the viewport distribution. Generally, up to 9 reflectors can be set on one reflector, and 3-5 layers can be designed. If too many reflectors are set, the angle between each detection area and the adjacent detection area will be small. It has no effect on the detection effect. On the contrary, the sensitivity is improved, which is easy to cause false alarm of the detector. Special attention should be paid in the design process.

Read recommendations:

The main purpose of ntc thermistor.Radar Microwave Induction Sensor Switch

Hand warmer suitable ntc thermistor

PIR Lens SIR650

Φ12mm size

PIR Lens 8605-2