Principle of infrared detection (infrared radiation detection)
The essence of infrared detection (infrared radiation detection) in the nondestructive testing technology method is to utilize the characteristics of infrared radiation of objects for non-contact infrared temperature recording method.
Infrared is a kind of electromagnetic wave, with radio waves and visible light of the same nature, the wavelength between 0.76 ~ 100μm, according to the range of wavelengths can be divided into near-infrared, mid-infrared, far-infrared, far-infrared, very far-infrared four categories, which is in the continuous spectrum of electromagnetic waves in the region of the radio waves and the visible light between the location. Infrared radiation is a natural existence of a wide range of electromagnetic radiation, it is based on any object in the regular environment will produce their own molecules and atoms irregular movement, and constantly radiating thermal infrared energy, molecules and atoms of the more intense movement, the greater the energy of radiation, and vice versa, the smaller the energy of radiation.
All temperatures in the zero degree (-273.15K °) above the object, will be due to their own molecular movement and constantly radiate infrared radiation to the surrounding space, the size of the object's infrared radiation energy and its distribution of wavelengths and its surface temperature has a very close relationship. Through the infrared radiation detector will be the power of the object radiation signal converted into electrical signals (on the object's own infrared radiation energy measurements), it can accurately determine the surface temperature, or through the output signal of the imaging device can be completely one-to-one correspondence to simulate the scanning of the object surface temperature spatial distribution, processed by the electronic system, transmitted to the display screen, and the object surface heat distribution of the corresponding thermal image map. The output signals can simulate the spatial distribution of temperature on the scanned surface exactly one to one. Using this method, you can realize the target for long-distance thermal state image imaging and temperature measurement and analysis and judgment, that is, the basic principle of infrared radiation detection.
Planck's blackbody radiation law: blackbody is an idealized radiation body, it absorbs all wavelengths of radiant energy, there is no energy reflection and transmission, the emissivity of its surface is 1. Although there is no real blackbody in nature, but in order to clarify and obtain the law of distribution of infrared radiation in the theoretical study must be selected as an appropriate model, which is Planck put forward by the body of the radiation of the cavity of the quantization of the vibronic model, thus deriving Planck's blackbody. Thus derived Planck's law of blackbody radiation, that is, expressed in wavelengths of the blackbody spectral radiance, which is the starting point of all infrared radiation theory, it is referred to as the law of blackbody radiation.
Almost all of the actual objects that exist in nature are not blackbodies. All the radiation of the actual object in addition to the wavelength of the radiation and the temperature of the object, but also with the composition of the object's material type, preparation method, thermal process, as well as the surface state and environmental conditions and other factors. Therefore, in order for the blackbody radiation law to apply to all real objects, a scaling factor, the emissivity, which is related to the nature of the material and the state of the surface, must be introduced. This coefficient expresses the closeness of the thermal radiation of a real object to the blackbody radiation, and has a value between zero and a value less than one. According to the law of radiation, as soon as the emissivity of a material is known, the infrared radiation properties of any object are known.
