Extremely Emissive V-Grooved Microstructure Made of SU-8 for Enhanced Radiative Cooling

For a structure to show radiative cooling property, it must have first, high reflectivity of above 90% in the wavelength range of 0.3 to 3 μm, and second, high emissivity for the wavelengths ranging from 8 to 13 μm, namely atmospheric transparency window. Being inspired by the architecture of microwave absorbers used extensively for antenna measurements, we proposed a novel microstructure with near unity emissivity that can be further developed for radiative cooling. To this end, we designed and analyzed a V-grooved multilayer periodic microstructure capable of perfectly emitting in the aforementioned wavelength range. Further, SU-8 is selected as the material of the proposed microstructure. SU-8 is the commonly used material in photolithographic based microfabrication and it is shown, for the first time, that its bulk optical properties are appropriate for radiative cooling purposes. The numerical simulations of the emissivity were performed through a semi-analytical computational technique known as Transmission-Line Formulation (TLF) which enables us to accurately and efficiently calculate electromagnetic radiations reflected from or transmitted through a multilayer structures composed of periodic layers of absorbing materials. It was demonstrated through the simulations that the average emissivity of the proposed microstructure can even exceed 99% in the wavelength range desired for radiative cooling.