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A PIR lens, also known as a Fresnel lens, is a thin sheet made from a polyolefin material. One side of its surface is smooth, and the other side is burned with concentric circles from small to large. This texture is designed by using the dry interference of light and according to the relative sensitivity and reception Angle requirements. The characteristics of Fresnel lenses include large area, thin thickness and long detection range.

Fresnel lens has two main functions: one is the focusing function, that is, the thermal infrared signal refraction (reflection) on the PIR; Second, the detection area is divided into several bright and dark areas, so that moving objects entering the detection area can generate changing thermoluminescent infrared signals on the PIR in the form of temperature changes.

The tooth design of Fresnel lenses enables them to achieve band-pass (reflection or refraction) effect on the specified spectral range. For example, in a passive infrared detector (PIR), the Fresnel lens can limit the frequency peak of the incident light to about 10 microns (the peak of infrared radiation of the human body), so as to achieve the focus and induction of the thermal infrared signal of the human body.

Fresnel lens is the "glasses" of infrared probe, its proper use or not directly affects the effectiveness of use. If properly used, it can give full play to the role of human body sensing, so that its application field continues to expand. On the contrary, if it is improperly used, it may lead to misaction and missing action, so that the user loses confidence in it.

In addition, the manufacturing process of Fresnel lenses is also an important factor in their performance. It is usually made of plexiglass and cannot be wiped with any organic solvent such as alcohol. When cleaning, you can first rinse with distilled water or ordinary water, and then wipe with absorbent cotton.

In short, Fresnel lens is an important optical element, which has a wide range of applications in passive infrared detectors and other fields. Its working principle and manufacturing process have an important impact on its performance and application.