FDTD Simulations inspired by the Daytime Passive Radiative Cooling of the Sahara Silver Ant

In the refrigeration cycle, a huge amount of energy is consumed by pumping heat from the cold reservoir to the hot reservoir. However, passive radiative cooling dissipates heat from sky-exposed surfaces to the cold universe by strong thermal radiation within the 8-13 μm electromagnetic spectrum and reflecting radiations elsewhere. This results in the surface temperature being perpetually lower than ambient. It is a potential scheme for dramatically conserving energy for refrigeration and space cooling in buildings. After the discovery of daytime radiative cooling, a wide range of materials have been found promising for an 8-13 μm wavelength range emissive solar reflective cooling device. Here, we consider the thermal selective emitter inspired by the thermoregulatory effect of triangular hairs on Sahara silver ants. FDTD simulations were utilized to optimize the biomimetic surface made of 8-13 μm wavelength range emissive materials such as SiO2 and polydimethylsiloxane (PDMS), and a bottom solar mirror. The result revealed improved emissivity in the transparency window by patterning triangular arrays on the surface.