High Contrast Far-Field Radiative Thermal Diode.

We propose a theoretical concept of a far-field radiative thermal rectification device that uses a phase change material to achieve a high degree of asymmetry in radiative heat transfer. The proposed device has a multilayer structure on one side and a blackbody on other side. The multilayer structure consists of transparent thin film of KBr sandwiched between a thin film of VO2 and a reflecting layer of gold. When VO2 is in its insulating phase, the structure is highly reflective due to the two transparent layers on highly reflective gold. When VO2 is in the metallic phase, Fabry-Perot type of resonance occurs and the tri-layer structure acts like a wide-angle antireflection coating achieved by destructive interference of partially reflected waves making it highly absorptive for majority of spectral range of thermal radiation. The proposed structure forms the active part of configuration that acts like a far-field radiative thermal diode. Thermal rectification greater than 11 is obtained for a temperature bias of 20 K, which is the highest rectification ever predicted for far-field radiative diode configurations.