Metamaterial-based passive radiative cooling technology

Abstract

Global warming causes temperature increase of the Earth. The efforts to reduce energy consumption by radiative cooling techniques have been designed over the years. However, radiative cooling can be achieved easily at night. However, there are limitations of radiative cooling in the daytime under the hot sun. With the development of metamaterials-based passive radiative cooling technology of the selective control over optical properties, radiative cooling under hot sun become possible now. The principle of metamaterial-based radiative cooling is to achieve almost perfect reflectivity in the visible and near-infrared spectrum between 0.3 to 2.5 µm and high thermal emission in the infrared atmospheric window region between 8 to13 µm as radiative cooling technology utilizes the atmospheric transparency window from 8 to 13 µm. And passively release heat from Earth into outer space. Based on the emission and reflection principle, plenty of studies have been performed on the use of different types of materials and structures to develop the radiative cooling system effectively. In this report, metamaterials and structures used for radiative cooling are analyzed.