4.12 Infraredradiation detection QObject, which absorbs completely radiations of any wavelengths falling on it in any temperatures, is called a blackbody that is, its emissivity 8=I Common objects other than a blackbody have the specific radiance 8<I, in other words, they cannot absorb totally the radiant power on their surfaces. Their emissivities are also smaller than a blackbody and are therefore called gray bodies
❑ 4.12 Infrared radiation detection Object, which absorbs completely radiations of any wavelengths falling on it in any temperatures, is called a blackbody, that is, its emissivity = 1 . Common objects other than a blackbody have the specific radiance 1 , in other words, they cannot absorb totally the radiant power on their surfaces. Their emissivities are also smaller than a blackbody, and are therefore called “gray bodies
4.12 Infrared radiation detection u The plancks law describes the radiation intensity distribution for an ideal radiator (blackbody ) under different temperatures W (4.131) T in which W,the energy emitted by wavelength in Wm.um the 1st radiation coefficient, CI=374.15 MWum/m2 C2-the 2nd radiation coefficient, C2=14388 umK T-the absolute temperature, in K λ- - the wavelength,inm
❑The Planck’s Law describes the radiation intensity distribution for an ideal radiator (blackbody) under different temperatures: 4.12 Infrared radiation detection − = 1 2 5 1 T C e C W （4.131） in which W —the energy emitted by wavelength ，in −2 −1 Wm m ； C1 —the 1st radiation coefficient， 4 2 1 C = 374.15MWm / m ； C2 —the 2nd radiation coefficient，C2 = 14388m K ； T —the absolute temperature，in K； —the wavelength，in m
4.12 Infraredradiation detection If we should heat an ideal radiator to various temperatures and determine the relative intensities at each wavelength, we would obtain characteristic energy-distribution curves such as those shown in Fig. 4.107. Not only is the radiation intensity of the higher-temperature body increased, but the wavelength of maximum emission is also shifted toward shorter waves(from red toward blue)
• If we should heat an ideal radiator to various temperatures and determine the relative intensities at each wavelength, we would obtain characteristic energy-distribution curves such as those shown in Fig. 4.107. Not only is the radiation intensity of the higher-temperature body increased, but the wavelength of maximum emission is also shifted toward shorter waves (from red toward blue). 4.12 Infrared radiation detection
4.12 Infraredradiation detection 90K 1800K 700F 600 500K 0 Fig. 4.107 Graphical representation illustrating the basis for Wiens displacement law
Fig. 4.107 Graphical representation illustrating the basis for Wien’s displacement law 4.12 Infrared radiation detection
4.12 Infrared radiation detection For a nonideal body, the intensity distribution must be multiplied by the emissivity a. the wavelength of peak intensity is given by the Wien's displacement law 2898/T (4.132)
❑ 4.12 Infrared radiation detection For a nonideal body, the intensity distribution must be multiplied by the emissivity, . The wavelength of peak intensity is given by the Wien’s displacement law: 2898/T (m) max = （4.132）