10401203;a2
Figure 22.8 Spectral radiant emittance of three types of radiators. 1: Spectral radiant emittance; 2:
Wavelength; 3: Blackbody; 4: Selective radiator; 5: Graybody.
10327303;a4
Figure 22.9 Spectral emissivity of three types of radiators. 1: Spectral emissivity; 2: Wavelength; 3:
Blackbody; 4: Graybody; 5: Selective radiator.
22.4 Infrared semi-transparent materials
Consider now a non-metallic, semi-transparent body – let us say, in the form of a thick
flat plate of plastic material. When the plate is heated, radiation generated within its
volume must work its way toward the surfaces through the material in which it is
partially absorbed. Moreover, when it arrives at the surface, some of it is reflected
back into the interior. The back-reflected radiation is again partially absorbed, but
144 Publ. No. T559382 Rev. a358 – ENGLISH (EN) – June 23, 2009
22 – Theory of thermography
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