Radiative cooling of earthbound objects for extreme and colored, and camouflaged operations

Abstract

Over 100 years after the discovery of Planck’s law, the principle of blackbody radiation has been an essential part of modern history as facilitating the birth of quantum dynamics and other numerous technologies that are deeply involved in human life. By revisiting the old but well-known principle, this thesis proposes feasible solutions to currently pressing issues: escalating cooling demand and indiscriminate surveillance. As a next-generation cooling system, terrestrial radiative cooling is spotlighted since it does not consume electricity during the cooling process, unlike the conventional air-conditioning system. In times of climate and energy crisis, it can be a very promising approach, but some important questions remain unanswered. First, previous studies have shown that sub-ambient cooling is possible via the radiative cooling process, but fundamentally, the ultimate cooling temperature and emissivity profiles that can achieve it have not been revealed yet. In addition, the exterior of the radiative cooling surface has been limited in ultra-bright colors for solar reflection, but it is unknown how to overcome the lack of color variety. Here, all the questions will be rigorously answered by clarifying performance boundaries in cooling temperature and color diversity, and furthermore, general approaches to overcome such limitations will be addressed. Another important topic of this work is to realize multi-band camouflages in diverse backgrounds. In recent years, advanced detection technologies have made it more difficult to ensure security in the civilian and military sectors by using conventional camouflage systems that operate in specific bands and specific backgrounds. As a counter-technology against surveillance, we present visual and thermal camouflage and maintain these functions in different ground-like environments based on a stack of electrochromic and emissive layers.