Fresnel lens is the "glasses" of infrared probe. It is just like human glasses. Whether it is properly used or not directly affects the efficacy of the use. The improper use of Fresnel lens will cause erroneous and leaky actions, which will cause users or developers to lose confidence in it. The function of human body induction is brought into full play properly and its application field is expanding constantly.

Fresnel lenses are manufactured by electroplating die technology and PE (polyethylene) material according to the principle invented by French photophysicist FRESNEL. The surface of the lens (0.5-0.8mm thick) recorded a circle of concentric circles from small to large, from shallow to deep, and the profile looked like serrated. There are many and dense circular lines with large induction angle and long focal length, and the deep induction distance and short focal length of circular lines are recorded. The closer the red light is to the concentric ring, the more concentrated and stronger the light is. Several concentric rings in the same row form a vertical induction region, and a horizontal induction section is formed between concentric rings. The more the vertical induction area, the larger the vertical induction angle; the longer the lens, the more the horizontal induction angle. When the number of segments is more, the human motion amplitude will be smaller, and when the number of segments is less, the human motion amplitude will be larger. The center circles of different regions interlace with each other to reduce the blind areas between sections. Blind areas are formed between regions, between sections and between sections. Because the lens is restricted by the angle of view of the infrared probe, the vertical and horizontal angles are limited, and the lens area is also limited. Lens are classified as rectangular, square and circular in appearance and single, double and multiple in function.

The following is a diagram of the appearance of commonly used lenses:

When a person enters the sensing range, the infrared light emitted by the human body is gathered through the lens on a concentric ring in a long-distance area A or a middle-distance area B or a short-distance area C. The concentric ring and the infrared probe have an appropriate focal length. The infrared light is just received by the probe, and the probe sends the light signal into the electronic circuit to drive the negative. Work. The whole way of receiving infrared light from human body is also called passive infrared moving target detector.

There are three main colours of lenses. First, the primary colour of polyethylene material is slightly transparent, with good transmittance and is not easy to deform. 2. White is mainly used to match the color of the shell. 3. Black is used to prevent strong light interference. Lens can also be combined with the appearance of the product color, so that the overall product more beautiful.

Each type of lens has a model (named after the year number + series number). The main parameters of the lens are as follows:

1. Appearance Description - Appearance Shape (Long, Square, Round), Size (Diameter). In millimeters.
Second, the detection range - the effective distance (meter) and angle that the lenses can detect.
3. Focus length - the distance between the lens and the probe window, the accuracy of which is expressed in decimal points of millimeters. The rectangular and square lenses should be curved to align the probe window in focal length. Cooperative Application of Lens and Probes - We usually use a dual-source probe to uncover the filter glass. There are two TO-5 materials which are particularly sensitive to the infrared wavelength of 7-14um connected to the field effect tube.

Fresnel lens principle and application download in detail.