Near-Field Thermal Radiation: Recent Progress and Outlook

Abstract

Any materials at temperatures higher than absolute zero emit electromagnetic waves due to the thermal fluctuations of free charges or ions. When two or more bodies at different temperatures are brought sufficiently close to each other with vacuum gap spacing smaller than the characteristic thermal wavelength, near-field radiative heat flux can exceed the far-field blackbody limit, governed by the well-known Stefan-Boltzmann law, by orders of magnitude. This article reviews the recent progress on both theoretical and experimental studies of near-field thermal radiation with an emphasis on its potential applications. Recent theoretical developments are presented, such as near-field radiation of general anisotropic materials and 2D materials, application condition of effective medium theory, and exact numerical methods for dealing with arbitrary particles or periodic nanostructures. Recent experimental achievements are also discussed, focusing on tip-plane and plane-plane configurations with various materials. The wide applications of near-field radiation are summarized in terms of thermal imaging, energy harvesting, and contactless thermal management such as modulation, rectification, and amplification. An outlook is provided on the promise of near-field thermal radiation in energy harvesting, novel thermal sources, and sensing, as well as the development of related fields such as reducing Casimir stiction, minimizing noise current, and increasing spontaneous emission rate. Challenges are also discussed, such as developing exact and fast computational techniques for complex metamaterials, understanding near-field radiation at extreme gap spacing, overcoming weak mode coupling in thermophotovoltaic (TPV) systems, measuring large-area plane-plane configuration at small gap spacing, and realizing devices based on near-field radiation.

Near-field heat transfer between graphene/hBN multilayers

“…Examples include surface phonon polaritons that can exist at the surface of polar dielectric materials such as SiO 2 and SiC, or surface plasmon polaritons (SPPs) that can be supported between metallic surfaces or structures [13][14][15][16][17]. Recently, it is demonstrated that surface plasmons in graphene can also achieve a similar role to enhance the photon tunneling between two graphene sheets [18].…”

“…This is the so-called photon tunneling and the resulted nearfield heat transfer rate can be orders of magnitude larger compared to the blackbody limit [6][7][8][9][10][11][12]. The enhanced radiative heat transfer finds numerous applications such as thermal energy harvesting, radiative cooling, and thermal imaging [2]. Continuous efforts have been devoted to exploring new materials or structures that can result in large heat transfer rates that can benefit these applications.…”

“…As one of the fundamental modes of heat transfer, radiative heat transfer plays an important role in a wide spectrum of applications from energy harvesting to thermal management [1][2][3][4][5]. In the far field, the maximum radiative heat transfer rate between two objects is restricted by the black-body limit.…”

Nanoscale Thermal Transfer – An Invitation to Fluctuation Electrodynamics

“…A selection of more recent reviews are [5][6][7][8][9][10][11][12][13]. The main idea may be explained by analogy to Brownian motion: instead of characterizing the motion of a particle by its thermal energy, one introduces microscopic trajectories that are perturbed by randomly fluctuating forces.…”

Near-field thermal electromagnetic transport: An overview

“…Moreover, a number of numerical methods have been adapted to near-field thermal radiation: the finite-difference time-domain method [37][38][39], the finite-difference frequencydomain method [40], the boundary element method [41], the method of moments [42] and the discrete dipole approximation, which has been referred to as the thermal discrete dipole approximation (T-DDA) [43,44]. Additional information about near-field thermal radiation modeling and its potential engineering applications can be found in the numerous review papers published during the past decade [28,[45][46][47][48][49][50][51][52].…”