Infrared thermal imagers are a very important application in many applications of infrared sensors, and are now more and more popular in the industrial and civilian markets.
In the movie, there is such a shot. In order to avoid the pursuit of the opponent holding the thermal imager, Schwarzenegger jumped into the bathtub filled with water to keep his temperature in line with the surroundings, trying to cover himself. Infrared signal source to avoid detection by thermal imager.
To understand why a thermal imager is so magical, you must first start with its working principle.
How infrared thermal imaging cameras work
All objects above absolute zero (-273 ° C) emit infrared radiation. The technique of converting the temperature distribution of the surface of an object into an image visible to an adult eye by using a special electronic device and displaying the temperature distribution of the surface of the object in different colors is called infrared thermal imaging technology, and the electronic device is called an infrared thermal imager.
The infrared thermal imager uses an infrared detector, an optical imaging objective and an optical scanning system to receive the infrared radiation energy distribution pattern of the measured object and reflect it on the photosensitive element of the infrared detector. There is a light between the optical system and the infrared detector. The scanning mechanism scans the infrared thermal image of the measured object and focuses on the unit or the spectroscopic detector, and the infrared radiation energy is converted into an electrical signal by the detector, and is amplified, converted or the standard video signal is passed through the television screen or monitored. The device displays an infrared thermal image.
This thermal image corresponds to the thermal distribution field on the surface of the object, but the thermal image distribution of the infrared radiation of each part of the actual target object is weak due to the lack of gradation and stereoscopic effect compared with the visible image. In the actual process, in order to judge the infrared heat distribution field of the measured object more effectively, some auxiliary measures are often used to increase the practical functions of the instrument, such as image brightness, contrast control, real calibration, pseudo color rendering, etc. Mathematical operations and processing.
It should be noted that the thermal image and the 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 target surface temperature distribution. In other words, the infrared thermal image is not directly visible to the human eye. The surface temperature distribution of the target becomes a thermal image representative of the target surface temperature distribution visible to the human eye.
Composition of infrared thermal imager
The thermal imaging camera consists of 5 parts:
1. Infrared lens: receiving and concentrating infrared radiation emitted by the measured object;
2. Infrared detector assembly: Turn the heat radiation model into an electrical signal;
3. Electronic components: processing electrical signals;
4. Display component: converts an electrical signal into a visible light image;
5. Software: Process the collected temperature data and convert it into temperature readings and images.
Classification of infrared thermal imagers
1. The infrared camera is divided into cooling type and non-cooling type according to working temperature.
Refrigerated Thermal Imager: A cryocooler is integrated into the detector. This device can lower the temperature of the detector. This is to make the thermal noise signal lower than the imaging signal and the imaging quality is better.
Uncooled thermal imager: The detector does not require cryogenic refrigeration. The detectors used are usually based on micro-bolometers, mainly polysilicon and vanadium oxide detectors.
2, infrared camera according to the function is divided into temperature measurement type and non-temperature measurement type
Temperature measuring type infrared camera: Temperature measuring type infrared camera can read the temperature value of any point on the surface of the object directly from the thermal image. This system can be used as a non-destructive testing instrument, but the effective distance is relatively short.
Non-temperature measuring type infrared camera: Non-temperature measuring type infrared camera can only observe the difference of heat radiation on the surface of the object. This system can be used as an observation tool with a long effective distance.
Infrared thermal imager features
Infrared thermal imagers have the following distinctive features compared to general inspection equipment:
1, the thermal imager can measure the temperature of moving objects, and ordinary temperature measuring instruments are difficult to do this;
2, can use the microscope head to measure the temperature of a few microns or less;
3, can quickly diagnose the equipment;
4. It will not cause interference to the measured temperature field;
5, the temperature range is large, depending on the model, generally can measure the range of 0 °C - 2000 °C;
6, high sensitivity, according to different models, can distinguish the temperature difference of 0.1 ° C or even smaller;
7, safe to use, due to the non-contact of the measurement, the thermal imager is very safe to use.
The development of infrared thermal imager
In 1800, British astronomer FW Herschel discovered infrared light. In the 1970s, thermal imaging systems and charge-coupled devices were successfully applied. At the end of the last century, infrared devices represented by focal plane arrays (FPA) were successfully applied.
The core of infrared technology is infrared detectors, which can be divided into four generations according to their characteristics:
The first generation (1970s-80s): mainly based on units, multiple components for optical machine serial / parallel scanning imaging;
The second generation (1990s-2000s): is a scanning focal plane represented by 4x288;
Third generation: gaze type focal plane;
The fourth generation: the system chip that is currently developing with large area array, high resolution, multi-band, smart and smart type, has high-performance digital signal processing function, and even has single-chip multi-band detection and recognition capability.
At present, the mainstream technology of uncooled focal plane detectors is a thermistor type microbolometer, which can be divided into two types: vanadium oxide detector and amorphous silicon detector depending on the thermistor material used.
The development of uncooled focal plane array detectors can meet the needs of some military applications and almost all civilian fields, realizing miniaturization, low price and high reliability, and has become a promising and market potential in the field of infrared detection imaging. The direction of development.
Advantages and disadvantages of infrared thermal imager
Advantages of infrared thermal imaging
1. Infrared thermal imaging technology is a passive non-contact detection and identification with good concealment.
Because infrared thermal imaging technology is a passive non-contact detection and recognition of the target, it is concealed and not easy to be discovered, so that the operator of the infrared thermal imager is safer and more effective.
2. Infrared thermal imaging technology is not subject to electromagnetic interference, and can accurately track thermal targets and accurately guide them at a long distance.
Since infrared thermal imaging technology utilizes thermal infrared rays, it is immune to electromagnetic interference. Infrared search and tracking system with advanced thermal imaging technology can accurately track hot targets at a long distance, and can track multiple targets at the same time, so that the weapon can play the most efficient.
Infrared thermal imaging technology can be accurately guided, so that the guided weapon has higher intelligence and the ability to not need to manage after launching, and can find the most important target to destroy, thus greatly improving the hit accuracy and making it powerful. Doubled.
3, infrared thermal imaging technology can truly achieve 24h all-weather monitoring.
Infrared radiation is the most extensive radiation in nature, while the atmosphere, clouds and the like can absorb visible light and near-infrared rays, but it is transparent to infrared rays of 3 to 5 μm and 8 to 14 μm. These two bands are called infrared window".
Therefore, by using these two windows, it is possible to clearly observe the target to be monitored on a completely dull night or in a harsh environment such as rain or snow. Because of this feature, infrared thermal imaging technology can truly monitor 24 hours a day.
4, infrared thermal imaging technology has a strong detection capability and a long range of action.
The ability to detect by infrared thermal imaging technology is strong, and it can be observed outside the range of enemy defense weapons, and its working distance is far.
At present, the handheld and mounted thermal imager on the light weapon allows the user to see the human body above 800m; the aiming distance is 2~3km; the water surface can be observed on the ship up to 10km; on the 1.5km high helicopter Ground-based individual activities can be found; on the 20km-high inspection plane, people on the ground and moving vehicles can be found, and changes in seawater temperature can be analyzed to detect underwater submarines.
5, infrared thermal imaging technology can use a variety of display methods, the human senses from five to six.
Only when the temperature of the object is as high as 1000 ° C or more can the visible light be visible to the human eye. All objects with temperatures above absolute zero (-273 ° C) will emit hot infrared rays. The thermal infrared energy emitted by a normal person is about 100W.
These are invisible to the human eye, but the amount of heat radiation energy of the object is directly related to the temperature of the surface of the object. This feature of thermal radiation allows people to use infrared thermal imaging technology for non-contact temperature measurement and thermal state analysis of objects, and can be displayed in a variety of display modes.
If the video signal is subjected to false color processing, the thermal image of different temperatures can be displayed by different colors; if the inverse video signal is subjected to analog-to-digital conversion processing, the temperature value of each point of the object can be displayed by digital, so that the human eye can not be seen. s things. So it can be said that infrared thermal imaging technology has increased human senses from five to six.
6. Infrared thermal imaging technology can visually display the temperature field on the surface of the object, which is not affected by strong light and is widely used.
The infrared thermometer can only display the temperature value of a small area or a certain point on the surface of the object, while the infrared thermal imager can simultaneously measure the temperature of each point on the surface of the object, visually display the temperature field of the surface of the object, and in the form of an image. display.
Since the infrared thermal imager detects the infrared heat radiation energy of the target object, it does not appear to be halo or closed when it is in a strong light environment like a low-light image intensifier, and thus is not affected by strong light.
In addition to military applications, infrared thermal imaging technology can also be widely used in civil, industrial, agricultural, medical, fire, archaeological, transportation, geological reconnaissance and other civil fields. Moreover, this technology can be applied to the security monitoring field in a large amount to facilitate intelligent security monitoring.
Disadvantages of infrared thermal imager:
1, the image contrast is low, the ability to distinguish details is poor
Since the infrared thermal imager is imaged by the temperature difference, and the general target temperature difference is not large, the contrast of the infrared thermal image is low, and the ability to distinguish details is deteriorated.
2, can not see through the transparent obstacles, such as window glass.
Because the infrared thermal imager is imaged by temperature difference, a transparent obstacle like window glass allows the infrared thermal imager to detect the temperature difference of the object behind it, so that the target cannot be seen through the transparent obstacle.
3, high cost, expensive
The cost of infrared thermal imagers is still the biggest factor limiting its widespread use, but with the advent of non-cooled infrared focal plane arrays, an effective means of obtaining high resolution, high reliability devices at low cost is provided. With the development of technology, breakthroughs in key technologies, and improved processing efficiency, future costs will be greatly reduced.
4, can not achieve long-distance monitoring, and the monitoring screen can only determine whether there are suspicious people entering, but can not see the face and appearance features
Thermal imaging cameras are widely used in both military and civilian applications. With the maturity of thermal imaging technology and the advent of various low-cost thermal imaging cameras suitable for civilian use, it has played an increasingly important role in various sectors of the national economy.
In industrial production, many equipments are often used in high temperature, high pressure and high speed operation. The infrared thermal imager is used to detect and monitor these equipments, which can ensure the safe operation of the equipment and find abnormal conditions in order to eliminate hidden dangers in time.
At the same time, the quality control and management of industrial products can also be carried out using infrared cameras. In addition, thermal imaging cameras have important applications in many fields, including medical, fire, archaeological, transportation, agriculture, and geology.
Such as building heat leak search, forest fire detection, fire source search, marine rescue, ore fracture identification and non-destructive inspection of various materials and products.
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