Passive and active working principle of infrared night vision device
Infrared night vision device is a military night vision device using photoelectric conversion technology. It is divided into two types: active and passive: the former uses infrared searchlights to irradiate the target, and receives reflected infrared radiation to form an image; the latter does not emit infrared rays, but relies on the target's own infrared radiation to form a "thermal image", so it is also called "thermal image". instrument". The infrared night vision devices currently on the market are all active. Passive infrared night vision devices are generally not called night vision devices, but are renamed thermal imagers.
1. Imaging principle of active infrared night vision device
Simply speaking: the principle of active infrared night vision device is to convert the invisible light (twilight or infrared light) signal from the target into an electrical signal, then amplify the electrical signal, and convert the electrical signal into the human eye. light signal.
Professionally speaking: The principle of the active infrared night vision device is to collect and intensify the existing light by focusing the light on the image intensifier through the eyepiece. Inside the intensifier, a photocathode will be "activated" by light and convert photon energy into Electrons, after being accelerated by an electrostatic region inside the intensifier, hit the phosphor surface screen (like a green TV screen), forming an image visible to the human eye; through the acceleration of the electrons, the enhanced Brightness and image clarity, as shown in the figure below.
Low-light night vision devices, in order to see objects at night, are visible to the naked eye through incremental processing of weak light. In order to achieve better results, the current low-light night vision devices are basically equipped with infrared emitters. It can be used as an auxiliary light when the light is too dark. But because it is easy to be discovered, which is what domestic enthusiasts often call "red exposure", it is basically used in the civilian market now.
2. Working principle of passive infrared night vision device (thermal imaging)
Principle: The thermal imaging infrared instrument is based on the basic principle that all objects above absolute temperature zero (-273°C) radiate infrared rays, and uses the difference between the infrared radiation of the target and the background itself to detect and identify the target.
Features: Due to the different intensities of infrared radiation of various objects, people, animals, vehicles, aircraft, etc. can be clearly observed, and are not affected by obstacles such as smoke, fog, and trees, and can work both day and night. It is the most advanced night vision observation equipment mastered by human beings. However, due to the high cost, it can only be used in the military at present. Although the application range of thermal imaging is very wide, there are huge markets in electricity, underground pipelines, fire protection, medical treatment, disaster relief, industrial inspection, etc., but it is still difficult to popularize.
