Applicability of the effective medium theory for optimizing thermal radiative properties of systems containing wavelength-sized particles

The effective medium theory (EMT) can be used for fast and approximate calculations of inhomogeneous media’s optical properties, which is helpful for considerably reducing computation times for designing the thermal radiative properties of particulate materials. Because EMT has mostly been limited to systems with characteristic sizes considerably smaller than the studied wavelength, this study explores the possibility to extend EMT’s applicability in particulate materials having structural sizes comparable to the radiation wavelength. Calculations are demonstrated for two types of thermal radiative properties: the extinction coefficient of a thermal insulating material and the reflectance of film solar absorbers. The results of the modified Clausius–Mossotti equation and Maxwell Garnett mixing rule are compared with methods based on more rigorous material structures and physical models. The applicable domains and limitations of the studied EMT methods are analyzed to provide a guide for utilizing EMT’s potential in aiding thermal radiative property design.