Near-field thermal electromagnetic transport: An overview

TL;DR

This paper introduces a comprehensive formalism for near-field thermal electromagnetic transport based on fluctuational electrodynamics, applicable to arbitrary shapes and sizes of heat sources, and demonstrates its application to a three-sphere system.

Contribution

It develops a size- and shape-independent formalism for near-field thermal electromagnetic transport, extending classical scattering theory to include thermal emission effects.

Findings

Thermal power distribution is slightly affected by a third sphere depending on dielectric properties.

Sphere temperature remains uniform despite non-uniform power absorption due to dominant conduction.

The formalism can be adapted to traditional electromagnetic scattering solution methods.

Abstract

A general near-field thermal electromagnetic transport formalism that is independent of the size, shape and number of heat sources is derived. The formalism is based on fluctuational electrodynamics, where fluctuating currents due to thermal agitation are added to Maxwell's curl equations, and is thus valid for heat sources in local thermodynamic equilibrium. Using a volume integral formulation, it is shown that the proposed formalism is a generalization of the classical electromagnetic scattering framework in which thermal emission is implicitly assumed to be negligible. The near-field thermal electromagnetic transport formalism is afterwards applied to a problem involving three spheres with size comparable to the wavelength, where all multipolar interactions are taken into account. Using the thermal discrete dipole approximation, it is shown that depending on the dielectric function, the presence of a third sphere slightly affects the spatial distribution of power absorbed compared to the two-sphere case. A transient analysis shows that despite a non-uniform spatial distribution of power absorbed, the sphere temperature remains spatially uniform at any instant due to the fact that the thermal resistance by conduction is much smaller than the resistance by radiation. The formalism proposed in this paper is general, and could be used as a starting point for adapting solution methods employed in traditional electromagnetic scattering problems to near-field thermal electromagnetic transport.