抄録
The thermal emissivity ε of a freely radiating body with a partially transparent surface layer and the dependency of ε on the thickness d of the layer are studied. Cholesteric liquid crystal films of various thicknesses (d=13∼33μm) and a sufficiently thick (d≅1mm) one, prepared on an Al evaporated, reflecting glass surface, were chosen for experiment.
When examined by a pyroelectric IR sensor, a relationship which includes a differential coefficient may be established between the radiance and the temperature of the film. The differential coefficient may be compared with that of blackbody radiation. The comparison has given the value of ε as a function of d, and the absorption coefficient to be 7.24×10-3μm-1.
The dependency of ε on d thus obtained is consistent with the formulation developed here after McMahon's theory of radiant characteristics of the partially transparent films.
