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FRESNEL LENS USED IN INFRARED SENSOR SYSTEM
Summary
Infrared sensing systems can be divided into five categories according to their functions. They are measurement systems that use infrared as the medium. According to the detection mechanism, they can be divided into photon detectors and thermal detectors. Infrared sensing technology has been used in modern science and technology, national defense, industry and agriculture, etc. It has been widely used.
Infrared technology has developed to this day and is already well known to everyone. This technology has been widely used in modern technology, national defense technology, industrial and agricultural technology and other fields. Infrared sensing system is a measurement system using infrared as the medium, which can be divided into functions Five categories: (1) Radiometer, used for radiation and spectrum measurement; (2) Search and tracking system, used to search and track infrared target, determine its spatial position and track its movement; (3) Thermal imaging system , It can produce the distribution image of the entire target's infrared radiation; (4) Infrared ranging and communication system; (5) Hybrid system refers to a combination of two or more of the above various systems.
Infrared Sensor System
It is mainly made of a material with high pyroelectric coefficient, such as lead zirconate titanate ceramics, lithium tantalate, triglyceryl titanium sulfate, etc. The detection element with a size of 2*1mm is made. One or two are installed in each detector. The detection element is connected in series with the two detection elements in reverse polarity to suppress the interference caused by the rise of its own temperature. The detection element converts the detected and received infrared radiation into a weak voltage signal, which is installed in the probe The field effect tube is amplified and output outward. In order to improve the detection sensitivity of the detector and increase the detection distance, a Fresnel lens is generally installed in front of the detector. The lens is made of transparent plastic. Each of the two parts is divided into several equal parts to make a lens with a special optical system, which cooperates with the amplifying circuit to amplify the signal by more than 70 decibels, so that the movement of people within a range of 10 to 20 meters can be measured. Now the infrared sensor system with Fresnel lens has been widely used in many fields, such as: human body temperature sensing, smart home system, robot ai field, and various human infrared sensing fields.
The infrared rays of other wavelengths are Absorbed by the Fresnel lens
The central wavelength of infrared radiation emitted by the human body is 9~10-um, and the wavelength sensitivity of the detection element is almost stable in the range of 0.20-um. A window equipped with a Fresnel lens is opened at the top of the sensor, this Fresnel The wavelength range of light that the pediatric lens can pass is 7~10-um, which is just suitable for the detection of human infrared radiation, and the infrared rays of other wavelengths are absorbed by the Fresnel lens, thus forming a special purpose for detecting human radiation Infrared sensor.