When it gets cold outside, and we want to move closer to a warm radiator or electric heater, we don't even need to touch them. Warm currents of air reach us even at a distance. This infrared radiation is part of the electromagnetic spectrum. We act as rough “recorders” of infrared radiation, operating with sensations: “warmth,” “hot,” and, of course, there is no question of any accuracy in determining temperature up to a degree. This will require special electrical measuring instruments that also “feel” invisible rays, showing a digital result since they are based on the principle of infrared thermography.
When Was Thermal Imaging Invented and Who
The first attempt to create thermal imaging can be called a device for recording evaporation. An oil film was used as a transducer. The temperature difference between the observed object and the environment was recorded and converted into the difference in film thickness. When heated, uneven evaporation of the liquid occurred, and thus, the object was displayed. The basis of its creation was the experiments of William Herschel back in the 19th century, who used filter paper soaked in alcohol and smoked from the side of the observed object. Herschel measured the temperature of each color, but in total, arithmetically, he did not reach the temperature emitted by sunlight. Long experiments did not help in finding the answer to the question. One day during a lunch break, the scientist left a sensitive thermometer near the red part of the spectrum. When he ate and returned to his workplace, he suddenly discovered a significant increase in a randomly measured temperature. Thus, the “missing” temperature was obtained, which, according to the spectrum, lies beyond the “red” part of the spectrum visible to our organs of vision, i.e., in a visually invisible area. The radiation comes from the Sun and, in general, from any warm object in the usual sense but also whose temperature is above absolute zero. The scientist concluded that he had indirectly discovered an area of new invisible radiation by the observed heating effect. Thus, the radiation received a precise thermal categorization.
How Thermal Imaging Started
Word «infrared» appeared later, at the end of the 19th century. Since then, however, IR rays have been associated primarily with heating, although the radiation discovered by Herschel belongs to the spectrum of light. Human does not consider light because he does not see it themselves. Interestingly, the human eye perceives both the visible (optical) image and infrared, but the brain is "imprisoned" by a narrow spectrum. The organs of human vision perceive radiation but do not transmit it to the brain. At the beginning of the 20th century, there were attempts to improve the device, and some success was achieved in America, Germany, and other countries. However, all devices belonged to the class of non-scanning devices and were not widely used due to the subject's low resolution and playback speed. In the 1950s, the development of a thermal imaging device began in many countries, where the primary attention was directed to the optical-mechanical scanning system since, at that time, the transmitting television tubes were not sufficiently sensitive to infrared radiation, and the leading indicator was the image transmission time. According to this principle, they were classified as low-speed, medium-speed, and high-speed. The first high-speed thermal imagers appeared in the 60s of the 20th century, the moment from which the active development of the thermal imaging industry began.
The experience of previous generations and the rapid growth of science and technology served as a stimulus for the development of solid-state matrices. It was proved that with the help of silicon, it is possible to convert optical to electrical signals. With the use of shift registers, individual elements of the matrices located along the periphery were scanned in two perpendicular directions. In the 70s, analogs of logs appeared, acting as signal custodians, which are then decoded by special devices and broadcast as images. At present, supersensitive uncooled bolometers are the most widely used. Thermal imagers are used in many areas of industry where control over temperature changes is required. Creating a small-sized but highly efficient device makes it possible to use it when performing various field tasks.
First Uses of Thermal Imaging Cameras
After the end of World War II, active research began on the creation of a beamless device. Programs for the development of "passive" equipment were carefully classified. The state of development of infrared technologies was carefully hidden. Only from the beginning of the 1950s did instruments based on these physical phenomena begin to serve the benefit of peaceful construction. The natural evolution of thermal imagers started in the USA, where its prototype was invented. In 1954, devices operating on infrared radiation began to be used on board aircraft. In the 60s, the Swedes developed a model of a thermal imager that looked more like a telescope. All models of this generation had a large mass and required additional cooling. In the early 1970s, batteries were used to power thermal imagers.
Since then, instruments have become portable, but a thermal standard in the field of view was required. In 1978, this shortcoming was eliminated. In addition, the function of recording images on film has been added. This model was already close to those we know today. Infrared energy is just one part of the electromagnetic spectrum, which includes gamma rays, X-rays, ultraviolet, thin visible light, infrared, terahertz waves, microwaves, and radio waves. They are all related and differ in wavelength (wavelength). All objects emit a certain amount of black body radiation depending on their temperature. The higher the temperature of an object, the more infrared radiation is emitted as blackbody radiation. A special camera can detect this radiation the same way a conventional camera detects visible light. It works even in complete darkness because the level of ambient light does not matter. This makes it useful for rescue operations in smoky buildings and underground.
Thermal imaging devices have many other uses. For example, firefighters use it to see through smoke, locate people, and locate fires. With the help of a thermal imager, power line maintainers detect overheating of connections and parts, which is a clear sign of their failure, to eliminate potential hazards. When thermal insulation fails, building professionals can see heat leaks to improve the cooling or heating efficiency of the air conditioning. Thermal imaging cameras can be roughly divided into two types: cameras with cooled infrared image detectors and cameras with uncooled detectors. Initially developed for military use during the Korean War, thermal imaging cameras have gradually made their way into other fields, such as medicine and archeology. Recently, price cuts have encouraged the introduction of infrared viewing technology. Advanced optics and sophisticated software interfaces continue to increase the versatility of IR cameras. The functionality of modern thermal imagers is enormous: a large number of external interfaces, parallel recording of infrared and video images, saving frames to internal memory and working with various special programs. The appearance of some thermal imagers resembles a video camera - but this impression is deceptive: thermal imagers are much more complicated, and recording a video image on such a device may be only a secondary option.
Thermal imagers are often confused with night vision devices, although their difference is significant. The classic night vision device allows you to navigate low light levels by amplifying the light entering the lens. In many cases, a bright object in the field of view "blinds" the device. They try to deal with this, sometimes - well, sometimes - in inexpensive mass devices - not very well. The thermal imager does not need light. It, of course, can be used as a night vision device, only the problem is solved differently here. The well-known philosophical construction about darkness as the absence of light has been adopted in thermal imaging technology: we look at what is, in this case, heat.