Active infrared vs. passive infrared infrared camera analysis

Active infrared technology in four forms

    As security issues gradually become the focus of social attention, the development of security monitoring technology has received more and more attention from all walks of life. Visible light monitoring alone can no longer meet people's monitoring requirements. 24-hour continuous monitoring is an indispensable and important part of the current monitoring system.

　　The technology to achieve night vision for cameras currently uses infrared night vision technology. Infrared camera technology is divided into two types: passive infrared camera technology and active infrared camera technology.

　　1. Passive infrared camera technology uses the principle that any object can radiate electromagnetic waves above absolute zero (-273℃). Due to the different radiation capabilities of different objects or even different parts of the same object and their different reflection strengths of infrared rays, the radiation differences between the object and the background environment, and the radiation differences between different parts of the scene itself, the infrared detector can convert the radiation signals of varying strengths into corresponding electrical signals, and then form a video image that can be observed by the human eye after amplification and video processing. The thermal image can show the radiation fluctuations of various parts of the scene, thereby showing the characteristics of the scene.

　　The thermal image and visible light image of the same target are different. It is not a visible light image that can be seen by the human eye, but an image of the temperature distribution on the target surface. It cannot clearly identify the detailed features of the target and cannot meet the requirements as "evidence". In addition, passive infrared cameras are expensive and are mostly used in the military. Currently, they are rarely used in the field of surveillance.

　　2. Active infrared camera technology uses "infrared light emitting diodes" to artificially generate infrared radiation, which is invisible to the human eye but can be captured by ordinary cameras, to assist in "illuminating" the scene and environment. The image sensor of the camera can sense the characteristics of infrared light, sense the infrared light reflected back from the surrounding environment, obtain a clearer black and white image, and realize night vision monitoring. Therefore, most of the current infrared camera technology uses active infrared camera technology, which uses infrared lights to cooperate with cameras.

　　There are currently four relatively mature forms of active infrared technology:

　　1. Traditional LED infrared lamp: It is composed of a certain number of infrared light-emitting diode matrices. The infrared emitting diode is made of a PN junction made of materials with high infrared radiation efficiency. A forward bias voltage is applied to the PN junction to inject current to excite infrared light. The spectral power distribution is a central wavelength of 830~950nm, and the half-peak bandwidth is about 40nm. It is a narrow-band distribution and is within the range that CCD can sense.

　　2. The second generation of array integrated infrared light source: Based on the original LED infrared technology, it adopts advanced packaging technology to package dozens of high-power and high-efficiency infrared crystals on a plane, integrate multiple infrared light-emitting chips in a small range, and perform "thermal and electric separation" processing, so that the entire part can be placed on a heat sink of any size and shape, thus solving the heat dissipation problem and no longer damaging other surrounding electronic components due to high temperature.

　　3. The third generation dot matrix infrared light source: using highly integrated LED array chip technology, the output of a single LEDArray is about 800mW~3.6W, the electro-optical conversion efficiency is about 25%, the light source is a single light source, and the light-emitting angle can be large or small.

　　4. Laser infrared light: It is a semiconductor laser. It uses the process of hole and electron recombination in semiconductor materials and the reduction of electron energy levels to release electrons to generate light energy. Then the photons form lasers in the propagation direction of the resonant photons. Lasers have good directionality, which is manifested in the small angle of the beam and concentrated energy. There is still enough light intensity when propagating to a longer distance, so it is very suitable for long-distance lighting.

Comparative analysis of imaging effects of various infrared technologies

　　2. Comparative analysis of imaging effects of various infrared technologies

　　1. Comparison between active infrared technology and passive infrared technology:

　　Cameras with active infrared technology need to rely on infrared emitting lamps. The advantage is that they can present detailed features of the target and have low cost. The disadvantage is that their irradiation distance is relatively short and the imaging effect is easily affected by the environment, especially in severe weather such as fog, snow, and rain. They are mainly used for detecting targets.

　　Cameras using passive infrared technology do not require auxiliary light sources. Their advantages are strong penetration and long illumination distance. Their disadvantages are that they can only present images of the temperature distribution on the target surface and are mainly used for target detection.

　　2. Comparison of four active infrared technologies:

　　1) Traditional LED infrared lamps are the most commonly used infrared light-emitting components, accounting for more than 95% of the market, but the quality varies greatly and the price varies greatly;

　　Its advantages are small size, simple production process, easy quality assurance, low heat generation, and reasonable luminous optical system. It can have no red burst (using 940-950nm wavelength) or only weak red burst (red burst is visible red light). Its service life can reach more than several thousand hours. It is an ideal device for infrared lamps and is currently widely used in night vision monitoring.

　　Its disadvantage is that the heat dissipation is not good, which causes the surrounding temperature to be too high and affects the life of nearby electronic components (such as camera boards, control circuit boards, etc.). The most criticized thing is that its light decays too quickly, and generally the night vision screen cannot be seen clearly in less than a year. Because it is encapsulated with "epoxy resin", "epoxy resin" will break when exposed to heat. Over time, there will be more and more fracture surfaces. When infrared light passes through each fracture surface, part of the light will be refracted. This is the main reason why traditional LED lights decay quickly and have a short life.

　　2) The second generation of array integrated light source integrates multiple infrared light-emitting chips in a small area and performs "thermal and electrical separation" so that the entire part can be placed on a heat sink of any size and shape, thus solving the heat dissipation problem and no longer damaging other surrounding electronic components due to high temperature. Also, due to the use of silicone packaging, the material does not break and greatly reduces light attenuation, and the life span is 5-10 times longer than that of traditional LED lights.

　　The disadvantage is that the price is much higher than that of traditional LED lights. In addition, when using lenses to narrow the light transmission angle in order to match the angle of the camera lens, it is inevitable that many light points deviate from the center of the lens (commonly known as: eccentricity phenomenon), resulting in poor light transmission efficiency. Compared with traditional LED lights of the same power, "not bright enough" is its disadvantage.

　　3) The third generation of dot matrix infrared light source (LEDArray) has an electro-optical conversion efficiency of about 25%, which is 2.5 times higher than the first generation of ordinary infrared LED (about 10%), reducing power consumption; the output of a single LEDArray is about 800mW~3.6W, and the brightness is about 100 times that of a conventional single LED output of 5~15mW; the effective life of LEDArray is 10,000h, which is more than 5 times higher than the effective life of ordinary LED; it is made of metal, easy to keep low temperature during operation, and has good heat dissipation performance; the half-power angle of LEDArray is 10°~120°, which can produce a (180° shape) luminous surface, solving the "flashlight effect" of ordinary LED indoor space that cannot be evenly illuminated; LEDArray is a highly integrated chip, so its volume is much smaller than other infrared products under the same brightness index;

　　The third generation of dot matrix infrared light source is closer in price to traditional LED. It is the best technology in the current infrared lighting market and is slowly replacing traditional LED infrared lighting technology.

　　4) Laser lighting technology can reach up to 3,000 meters, which is more than 20 times the irradiation distance of conventional products (120-150 meters). Laser has good directionality, a small beam angle, concentrated energy, and sufficient light intensity even at a long distance, so it is very suitable for long-distance lighting, suitable for large-scale environmental monitoring, forest fire prevention, scenic area monitoring, port terminal monitoring, oil field monitoring, etc.

　　However, the production process of laser infrared lamps is not like that of LED infrared lamps, and its production process requirements are very high. At the same time, the production of laser infrared lamps requires a huge investment, which is also beyond the reach of ordinary manufacturers.

　　3. Future development direction of infrared cameras

　　The current infrared camera market is quite chaotic, mainly because the industry lacks unified standards and specifications. For example, the irradiation distance of infrared lights is often the highlight of each company's publicity, and it is different from one company to another. However, there is no way to know under what conditions the irradiation distance is measured, what the ambient illumination is at that time, and what the quality of the image presented is. This is the most severe test currently facing infrared cameras, and solving this problem has become the focus of common concern among companies.

　　Active infrared technology has developed from an early efficiency of only 5% to the current LED Array technology with an efficiency of 25-30%, meeting the breakthrough of infrared night vision technology from short to medium and long distances. Laser lighting technology is one of the best ways to achieve long-distance night vision monitoring, and the light intensity is much stronger than conventional light sources. Long-distance night vision technology is a trend in the future night vision monitoring market.

　　The integration of active infrared technology and passive infrared technology will be one of the future trends. The passive infrared technology's strong penetration and long irradiation distance can be used to detect targets, and the active infrared technology's lighting principle can be used to collect target details, which can provide powerful "evidence" for medium and long-distance monitoring.

　　In addition, integration with another night vision technology - low-light technology, is also one of the future development directions. In a period when low-light and infrared technologies are constantly improving, considering the complementarity of the two, how to fuse low-light images with infrared images to obtain better observation effects without increasing the difficulty of existing technologies, these two technologies have become hot research topics in the current development of night vision technology.