Fresnel lenses are sheets, circles or other shapes that are injection molded or molded from polyolefin materials.
There are two main functions of the Fresnel lens on the probe: one is the focusing effect, which is to refract (reflect) the pyroelectric infrared signal on the PIR, and the second function is to divide the detection area into several bright areas and dark areas. The zone enables a moving object entering the detection zone to produce a varying pyroelectric infrared signal on the PIR in the form of a temperature change.
Simply put, there are equidistant ridges on one side of the lens. Through these ridges, the bandpass (reflection or refraction) of the specified spectral range can be achieved. The traditional bandpass optical filter for polishing optical equipment The cost is expensive. Fresnel lenses can greatly reduce costs. A typical example is the PIR (Passive Infrared Detector). PIR is widely used on alarms. If you take a look, you will find a small plastic hat on each PIR. This is the Fresnel lens. The inside of the small hat is engraved with a tooth pattern. This Fresnel lens limits the peak frequency of incident light to around 10 microns (the peak of human infrared radiation). The cost is quite low.
The Fresnel lens can focus the light transmitted through the narrow-band interference filter on the photosensitive surface of the silicon photodiode detector.
The Fresnel lens is made of plexiglass and cannot be wiped with any organic hydrazine such as alcohol. When removing dust, rinse with distilled water or ordinary clean water first, then wipe with absorbent cotton.
Fresnel lens is the "glasses" of the infrared probe. It is like the human glasses. Whether it is used properly or not directly affects the function of use. Misuse and misuse can cause the user or developer to lose it. confidence. Proper use of the role of human body induction, its application areas continue to expand. Shandong Yuying can customize the infrared lens according to customer requirements, generally take samples for 30 days.
Fresnel lens is more than a ring line, and the dense sensing angle is large, and the focal length is far; the deep sensing distance of the ring line is far, and the focal length is close. The more the infrared light is in the concentric ring, the more concentrated and strong the light. A plurality of concentric rings in the same row form a vertical sensing zone, and a horizontal sensing segment is formed between the concentric rings. The more the vertical sensing area, the larger the vertical sensing angle; the longer the lens, the more the horizontal sensing angle is. The number of segments is greatly affected by the movement of the human body, and the number of segments is small. The concentric circles of different zones are interdigitated to reduce the blind zone between the sections. A blind zone is formed between the zones and between the zones and between the segments. Since the lens is constrained by the angle of view of the infrared probe, the vertical and horizontal sensing angles are limited and the lens area is limited. The lenses are classified into appearances: long, square, and circular. The functions are classified into single-segment multi-segment, double-zone multi-segment, and multi-zone and multi-segment.
When a person enters the sensing range, the infrared light released by the human body is concentrated on the concentric ring of a long distance A zone or a medium distance B zone or a certain distance C zone through the lens, and the concentric ring and the infrared probe have an appropriate focal length. The infrared light is received by the probe, and the probe turns the optical signal into an electrical signal and sends it to the electronic circuit to drive the load. The entire way of receiving infrared light from the human body is also called a passive infrared active target detector.
The lens mainly has three colors, one, the primary color of the polyethylene material, slightly transparent, good light transmittance, and not easy to be deformed. Second, white is mainly used to adapt the color of the shell. Third, black is used to prevent strong light interference. The lens can also be combined with the appearance of the product to make the product more beautiful.
With the continuous expansion of the field of human body sensors, Fresnel infrared lenses are becoming more and more diverse, and the application is becoming more and more targeted.