Fresnel lens principle and application

The Fresnel optical lens is the “spectacles” of the infrared probe. It is just like the human eyeglasses. The proper use of the Fresnel lens directly affects the efficacy of the use. Improper use of the Fresnel lens results in malfunctions and leakages, causing users or developers to Loss of confidence. With proper use of human induction, the field of application is continuously expanding.

The principle invented by Fresnel, an optical physicist of the Fresnel optical lens, is formed by electroplating and PE (polyethylene) materials. The surface of the lens (0.5-0.8mm thick) is concentric with a circle ranging from small to large, outward to shallow, and looks like a sawtooth in profile. There are many ring lines and the dense sensing angle is large and the focal distance is far; the depth sensing distance of the circle line recording is far away and the focal distance is near. The closer the red light is to the concentric rings, the more focused and stronger the light. Several concentric rings in the same row form a vertical sensing area, and a horizontal sensing section is formed between the concentric rings. The more vertical sensing areas, the greater the angle of vertical sensation; the longer the lens, the more sensing segments the horizontal sensing angle will be. The number of sections that are sensed by the human body is much smaller, and the number of sections that are sensed by the human body is smaller. The heart circles of different zones are intertwined with each other, reducing the blind zone between segments. Between the district and the district, between the section and the section, a blind area is formed between the sections. Because the lens is limited by the angle of view of the infrared sensor, the vertical and horizontal angles should be limited, and the lens area is also limited. Lenses are categorized as appearances: long, square, and round, and they are classified as functional: single-zone, multi-zone, multi-zone, multi-zone, and multi-zone.

The following figure shows the appearance of commonly used lenses:

When the person enters the sensing range, the infrared light released by the human body is concentrated on the concentric rings of the long-distance A zone or a certain segment of the medium-distance B zone or the near-distance C zone through the lens. The concentric rings and the infrared probe have a proper focal length. The infrared light is just received by the probe. The probe converts the light 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 activity target detector.

There are three main colors of the lens, one, polyethylene material primary color, slightly transparent, good light transmittance, not easily deformed. Second, white is mainly used to adapt the shell color. Third, black is used to prevent strong light interference. Lenses can also be combined with product appearance color, make the product more beautiful overall.

Each lens has a model (named by year number + serial number), the main parameters of the lens:

First, appearance description - appearance shape (long, square, round), size (diameter). In millimeters.

Second, the detection range - refers to the lens can detect the effective distance (meters) and angle.

Third, the focal length - refers to the distance between the lens and the probe window, the accuracy of the decimal point as a unit of millimeters. Long and square lenses are to be curved in alignment with the probe window in focal lengths. Lens and probe with the application - we commonly use dual-source probe, uncover the filter glass, there are two points inside the TO- 5 material of 7 - 14um infrared wavelength is particularly sensitive to the field effect tube.