Generalized many-body approach for near-field radiative heat transfer between nonspherical particles

A generalized fluctuational electrodynamics-based many-body approach for calculating near-field radiative heat transfer (NFRHT) between nonspherical dipoles is proposed. The geometric parameters of nonspherical dipoles are implemented in the definition of the self-term of the free-space Green's function and, conversely to previous many-body models of NFRHT, dipole polarizability is defined a posteriori from the free-space Green's function solution such that polarizability calculation is an optional post-processing step rather than a required input. Both strong and weak forms of the generalized many-body approach are presented. It is shown that the approximate weak form is less computationally expensive but is only applicable to small particles characterized by size parameters less than ~0.24. The generalized many-body method is compared against an analytical solution for NFRHT between two spheroidal dipoles. Acceptable agreement is obtained, and the discrepancies are ascribed to differences in approximations for multiple reflections and from the way in which particle orientation is implemented in each method. The generalized many-body method is then applied to analyze the near-field spectral conductance between two SiC ellipsoidal dipoles. Results reveal that changes in the orientation of one of the ellipsoidal dipoles lead to active tuning of localized surface phonon resonance by up to three orders of magnitude. Finally, the spectral radiative thermal conductivity of a metamaterial composed of 1000 SiO2 ellipsoidal particles is studied. The metamaterial displays anisotropic radiative thermal conductivity, with differences in the value at resonance up to 2.8 times between different directions. The generalized many-body model of NFRHT presented in this paper may be used to develop particle-based metamaterials with novel, engineered radiative thermal properties.