Radiation-based Near-field Thermal Rectification via Asymmetric Nanostructures of the Single Material

Abstract

Typically, thermal diodes utilize the asymmetric theory of different materials to achieve thermal rectification. But according to our research, thermal diode made of the same material can also generate fairish thermal rectification through asymmetric nanostructures. Asymmetric heat fluxes is obtained by employing the temperature-dependence of coupled surface phonon polaritons modes in asymmetrical nanostructures. The thermal diode designed in this work contains a nanoporous plate and a plate, both made of silicon carbide. And the two terminals are separated by a vacuum gap of micro-nano scale. Thermal rectification is caused by the different degree of matching of the coupled surface phonon polaritons modes between the two terminals in the forward- and reverse-scenarios. Rectification efficiency is researched by varying contrivable parameters, namely the volumetric filling ratio $f$ , the vacuum gap $d$ , and the temperature of the emissive layer $T_{h}$ with the temperature of the receiving layer $T_{l}$ is equal to 300 K. In the framework of fluctuation electrodynamics, based on the effective medium theory and the scattering matrix method, calculations show that the thermal rectification efficiency can be maintained above 0.6 in the large fill ratio range (0.2 to 0.6) and a wide vacuum gap range (4 nm to 60 nm), when the temperature of the emissive layer and the receiving layer are 1000 K and 300 K, respectively. Thermal rectification efficiency can be further improved by changing the structure, such as using a grating, adjusting the optical axis, and using a multilayer structure.