Metamaterials for radiactive cooling

The increasing pressure of society to decrease energy consumption and to enhance energetic efficiency has lead to search novel technologies to accomplish it. Notwithstanding the increasing electricity production of renewable energies, it is a fact that the energy expenses can be drastically reduced in most areas. Among these areas, cooling systems stand out for being energetically inefficient. Furthermore, both economical and energy cost of such systems are increasing due to the global warming, which is aggravated by the energy production for them, making a loop that is increasingly damaging the environment. A solution to this problem has emerged under the name of radiative cooling, which is a physical phenomenon by which any terrestrial object losses heat in form of radiation that is sent to outer space. This process can be explained by black body radiation theory and the atmospheric window. The former states that any object at some temperature above 0 K radiates energy at all wavelengths, with its radiation peak and spectral location modulated by its temperature. The latter is a frequency band in which the atmosphere is transparent to radiation, making possible for waves at certain frequencies to cross freely. These phenomena allows a direct heat transmission between earth and space, which is cold and almost infinite, making a great storage for excess warmth without wasting energy in the process. In this work, it has been studied one of the main technologies that can implement radiative cooling in practice, metamaterials, with the aim to understand how to improve its associated problems of manufacturing and design for radiative cooling applications. In Chapter 1, the fundamentals of radiative cooling are introduced along with the state of the art. Then, Chapter 2 presents the materials used in the literature and in this work to develop later analytical models for thin film multilayered metamaterials and a possible way to automatically design them. To better understand the analytical developments, two appendices introducing the underlying theory and equations are included. Also, the software used in this work is presented. Finally, the performance and analysis of three different radiative cooling devices is exposed in Chapter 3, one of them using the materials and methods of Chapter 2.Máster Universitario en Ingeniería de Telecomunicación por la Universidad Pública de NavarraNafarroako Unibertsitate Publikoko Unibertsitate Masterra Telekomunikazio Ingeniaritza

Evolutionary algorithms applied to multi-layered radiative cooling metamaterials

A newly design method for designing multi-layered radiative cooling metamaterials based on genetic algorithms (GAs) is exposed. The developed GA has been tested in three cases, resulting in three different structures that achieve, theoretically under direct sunlight, a net cooling power of 39.96 W/m 2 , 57.78 W/m 2 and 61.77 W/m 2 . Such devices are composed of 9, 15 and 24 layers respectively with a total thickness of less than 4.8 µm in the worst case. By the nature of the method, fewer design experience in metamaterials is needed, as well as it is free-cost, due to the use of analytical calculations for the emissivity of the meta materials instead of a commercial generic electromagnetic solver. Automated design of radiative cooling multi-layered structures and other applications in the infrared range can be further developed with this work.This work has been performed in the frame of the project "Algoritmos EVOlutivos aplicados a dispositivos de enfriamiento radiativo pasivo ultracompactos basados en METAsuperficies (AEVOMETA II), funded by the Government of Navarre