Thermal radiation between closely spaced metal surfaces at low temperature due to traveling and quasi-stationary components of the radiation field

Abstract

Radiant heat-transfer effects between closely spaced parallel metal surfaces at low temperature are analyzed. The theory considers thermally induced fluctuating electric fields at the surface of the metal, similar to those responsible for Nyquist noise, as the source of the thermal radiation field in the vacuum space between the metals. Both traveling wave and quasi-stationary wave components of the thermal radiation field are shown to exist in the vacuum region due to these sources. The electric and magnetic field vectors associated with these fields existing in the vacuum space are derived utilizing standard electromagnetic boundary theory, and the resulting unidirectional heat fluxes are calculated using the Poynting theorem. The resulting heat fluxes are shown to correspond to highly unclassical heat-transfer effects when the product of spacing distance l and the surface temperature T is less than 1 cm °K. At small spacing distances the heat flux first rises in a manner inversely proportional to the spacing distance and then where lT ≲ 10 −2 cm° K, the unidirectional heat transfer rises inversely proportional to the fourth power of this product. The results of this theory are shown to be consistent with previous experimental measurements.