Conical Cavity Type Thermal Radiation Detector with Gold-Black Coating.

Abstract

The author fabricated a plain type thermal radiation detector with evaporating gold-black as the surface absorbent attached to a thermoelectric detector. The spectral responsivity of the thermal radiation detector under different evaporating conditions was investigated and the best condition for the highest degree of spectral responsivity is reported. The relative spectral responsivity of the thermal radiation detector with gold-black absorber against the thickness of the gold-black was explained with proposed plain type models. In the proposed plain type models, incident radiant energy is absorbed near the surface and transmitted through the gold-black absorber as heat. There were two kinds of the proposed plain type models, one was called the lumped constant model and the other was called the distribution constant model. Each model has two types. The best proposed model to fit the measured results was the distribution constant model 2, which contained reflection at the interface of the absorber and the PVDF pyroelectric film. To attain a very sensitive thermal radiation detector with constant spectral responsivity, which is constant within ±1% over a measured wavelength region, conical cavity type detectors were fabricated. Experimental samples were made to study the dependence of the effective reflectance of a conical cavity type thermal radiation detector on reflectance of the absorbent on the cone and the cone apex. The decrease in the effective reflectance for a conical cavity type was explained using a proposed conical cavity type model, which contains the first reflection, and the second repeated mutual reflections.