An Electromagnetic Model for Thermal Emission

Abstract

A rigorous model based on classic electromagnetism to characterize the thermal radiation of real ohmic media is presented in this thesis. This model explains the available energy due to thermal agitation inside ohmic material based on Johnson's theory of thermal noise in electric circuits. The field is expanded in a finite number of modes (degrees of freedom per unit of volume), which are all independent and orthogonal from each other and are eigenvectors of Maxwell's Equations. The minimum distance for two eigenvectors to be independent is found as half of the real effective wavelength in the medium, based on which an analytical expression of the total energy available by thermal agitation in the finite volume is given. Integrating Poynting vectors of sources over the entire object volume, an analytical expression to estimate the total spectral power radiated out by a real ohmic material body is derived, which does not utilize Planck's law of black body radiation as an intermediary. Finally, a measurement campaign is proposed aiming at providing accurate measurements of the thermal radiation from silicon samples of small dimensions in the mm and sub-mm wave range.