10401203;1
Figure 18.8 Spectral radiant emittance of three types of radiators. 1: Spectral radiant emittance; 2:
Wavelength; 3: Blackbody; 4: Selective radiator; 5: Graybody.
10327303;3
Figure 18.9 Spectral emissivity of three types of radiators. 1: Spectral emissivity; 2: Wavelength; 3:
Blackbody; 4: Graybody; 5: Selective radiator.
18.4 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 some of it arrives at the other surface, through which most of it
escapes; part of it is reflected back again. Although the progressive reflections
18.4 – Infrared semi-transparent materials
Publ. No. 1 557 536 Rev. a35 – ENGLISH (EN) – January 20, 2004 95
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