The key problem of individual thermal imagers as part of the instrumentation and sighting complex is the stringent requirements for weight and dimensions. It is impossible to place a system for cooling the matrix with liquid nitrogen, so new engineering solutions have to be looked for. And why bother to fence in the most complicated and expensive thermal imager, if there are already excellent infrared night vision devices for individual small arms? The point is in camouflaging the enemy, smoke, atmospheric precipitation and light interference, all this dramatically reduces the efficiency of night vision devices, even with third-generation electro-optical converters. The product of the Novosibirsk Central Design Bureau "Tochpribor" under the index 1PN116 is just designed to work in such conditions and is an old-school representative of devices for detecting infrared radiation of objects on the battlefield.
The 1PN116 thermal imaging sight with its keen vision sees everything the size of a person and what is hotter than the natural background 1200 meters ahead. The device has a significant mass (3, 3 kg), and therefore it is placed mainly on the SVD, machine guns "Pecheneg" and "Kord". An uncooled microbolometer with a matrix of 320x240 pixels is used as a "retina". Let's take a closer look at the tricks of uncooled thermal imaging.
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This technique is already the third generation, which has fundamental differences from the previous ones in the absence of a complex and not always reliable optical-mechanical scanning system. In this generation, thermal imagers are based on Focal Plate Area (FPA) solid-state array receivers, mounted immediately behind the lens plane. The "chemistry" of thermal vision in such gadgets, in the overwhelming majority of cases, is based on resistive layers of vanadium oxides VOx or amorphous silicon α-Si. But there are also exceptions, in which photodetectors or "hearts" of thermal imagers are based on PbSe, pyroelectric photodetector arrays, or matrices based on CdHgTe compounds equipped with thermoelectric cooling. It is interesting that such cooling is most often not used for its intended purpose, but only provides thermal stability under variable environmental conditions. Microbolometers from the VOx or α-Si series register changes in electrical resistance under the influence of temperature, which belongs to the basic principle of operation of a thermal imager. Each such solid-state sensor contains a signal preprocessing chip that converts the resistance to output voltage and compensates for the background radiation. An important requirement of a microbolometer is work in a vacuum and "heat-transparent" germanium optics, which seriously complicates the work of both designers and production workers. And the sensor itself must have a reliable substrate with inclusions of germanium or gallium arsenide. To understand all the intricacies of the microbolometer's work, it should be noted that fluctuations in the temperature of the crystal by 0, 1 K leads to a tiny change in resistance by 0, 03%, which must be tracked. All other things being equal, amorphous silicon has some advantages over vanadium oxides - the uniformity of the crystal lattice and high sensitivity. This makes the image for the user more contrast and less prone to noise, compared to a similar technique on VOx. Each pixel of the microbolometer is unique in its own way - it has its own, slightly different from its counterparts, gain and offset, which affect the final image. By increasing the number of pixels, reducing the pitch between them (up to 9-12 microns) and miniaturizing them, designers are trying, among other things, to reduce the noise level in the image. “Bad” or defective pixels are a serious problem in microbolometer manufacturing, forcing engineers to develop software mechanisms to eliminate white or black dots on the screen and flickering particles. This is usually organized using interpolation, that is, the outgoing signal from the "broken" pixel is replaced by the derivative from the value of the neighbors. The most important parameter of the matrix is the NETD (Noise Equivalent Temperature Difference) value or the temperature at which the microbolometer distinguishes the signal from the noise. Of course, the sensor needs to be fast, so the next parameter is the time constant or the rate at which the imager reacts to changes in temperature. Fill factor or fill factor is a matrix characteristic reflecting the level of filling of the microbolometer with sensitive elements, the larger it is, the better the image is seen by the operator. Hi-tech matrices can boast of 90% coverage of the matrix with the number of pixels reaching 1 million. The user can observe the battlefield in two versions - monochrome and color palette. Military and security products usually generate a monochrome image, since the clarity of the enemy's figures and his equipment is much higher than the color version.
The developments of American scientists regarding the use of graphene as an infrared sensor look promising. They are trying to introduce this 2D material everywhere, and now the turn has come to thermal imaging technologies. Considering that 70-80% of the cost of an uncooled thermal imager is made up of a microbolometer and germanium optics, the idea of creating graphene thermoelectric sensors is very tempting. According to the Americans, one layer of relatively inexpensive graphene on a silicon nitride substrate is enough, and the prototype is already acquiring the ability to distinguish a person at room temperature.
Both abroad and in Russia, much attention is paid to developments related to athermalization of the optical systems of thermal imagers, that is, resistance to ambient temperature extremes. Lenses are used from chalcogenide materials - GeAsSe and GaSbSe, in which the refractive indices of the rays depend little on temperature. LPT and Murata Manufacturing have developed a method for producing such lenses by hot pressing, followed by diamond turning of aspherical and hybrid lenses. In Russia, one of the few manufacturers of athermal lenses is JSC NPO GIPO - State Institute of Applied Optics, which is part of the Shvabe holding. The lens material is oxygen-free glass, zinc and germanium selenides, and the body is made of high-strength aluminum alloy, which ultimately guarantees no distortion in the range from -400C to + 500C.
In Russia, in addition to the mentioned 1PN116 from FSUE TsKB Tochpribor (or Shvabe-devices), a much lighter thermal imaging sight "Shakhin" (JSC TsNII "Cyclone"), named for "vigilance" in honor of the predatory species of falcon, characterized by the French Ulisse matrix with 160x120 pixels (or 640x480) and a recognition range of a height figure of 400-500 meters. In the latest generations, the imported microbolometer was replaced with a domestic model.
Further on the list: PT3 thermal imaging sight from Novosibirsk "Shvabe - Defense and Defense" with a matrix resolution of 640x480 elements, weighing 0, 69 kg and, which has become the "gold standard", a detection range of a growth figure of 1200 m. The pixel pitch of this sight is not is an outstanding indicator and is 25 microns, which forms a modest final image resolution. By the way, the holding organized the production of a hunting sight based on a military design under the code PTZ-02. Another representative of the domestic design school is the Alfa TIGER thermal imaging sight from the Shvabe-Photopribor division, which seems to be a monopolist, with a microbolometric receiver in the range of 7-14 microns with a resolution of 384x288 pixels. In "TIGER" the operator works with a monochromatic OLED microdisplay of 800x600 pixels, of which 768x576 are reserved for displaying a thermal image. An important difference from the early models of Russian thermal imaging sights is the increased operating time by 30 minutes - now you can fight in the infrared range for 4.5 hours. Its modification "Alpha-PT-5" has a rare PbSe photodetector with electrical thermal stabilization. The universal sight PT-1 from NPO NPZ is capable of combining with many types of small arms due to a special mount and memory, in which ballistics and reticle are programmed for a wide range of weapons. Squeezing the sight eyecup with the muscles of the eye turns on the microdisplay, and unclenching it turns off - this is such an energy saving system implemented in the PT-1. American microbolometers are installed on the thermal imaging device for aiming and observation "Granite-E" from ISPC "Spectrum". The technique with "wide-polar" vision is presented by the company with the long name NF IPP SB RAS "KTP PM" under the index TB-4-50 and has a field of view of 18 degrees by 13.6 degrees.
By the way, the company offers a range of three standard sizes of thermal imaging sights TB-4, TB-4-50 and TB-4-100, equipped with a modern microprocessor for image processing based on the HPRSC architecture (High Performance Reconfigurable Super Computing). A separate direction is the new Mowgli-2M thermal imaging sights under the 1PN97M index, installed on the Strela-2M, Strela-3, Igla-1, Igla, Igla-S type MANPADS family and the newest Verba . They develop and assemble sights at the St. Petersburg LOMO and they differ, of course, by a huge detection range of 6000 m. An alternative to Mowgli can be TV / S-02 sights from the BELOMO company from the near abroad, designed for heavy small arms - large-caliber rifles, grenade launchers and, in fact, MANPADS. With a mass of no more than 2 kg, the Belarusian sight demonstrates an impressive range of human detection of 2000 meters, and recognition of 1300 meters.
In this part of the "Thermal Imaging Chronicles" we talked about some domestic thermal imaging individual sights and their counterparts from the near abroad. Ahead are foreign analogues, tank thermal imagers, as well as individual observation and reconnaissance devices.
