BUSCADOR RECOLECTA

Electromagnetic absorbers serve as fundamental components for a wide range of applications, encompassing energy and heat management, sensing, and communications. In this study, we explore several complex permittivity combinations for lithography-free material-reflector and material-spacer-reflector configurations that lead to perfect absorption peaks across distinct permittivity regimes and varying thicknesses. We provide an extensive analysis of angle and polarization dependencies, specifically using silicon carbide as an illustrative example. Our findings reveal the potential for harnessing different absorption regimes within a single device, thus enabling the realization of multiband absorption capabilities. Furthermore, we demonstrate perfect absorption linked with extreme values of permittivity, and we find the conditions to get perfect absorption in ultrathin slabs. In addition, we carry out an analysis about the response at oblique incidence, and we identify a particular mode in the negative permittivity region and its hybridization with epsilon-near-zero modes at oblique incidence. This investigation serves as a valuable standardization of absorber design, offering insights to develop perfect absorbers for infrared applications such as thermal emission, communications, and sensing., The research presented in this paper has been supported by funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 964450 (MIRACLE project, more information available in Ref. ) from the EU Commission. Additionally, this work has received financial support from Project No. TED2021-132074B-C33, funded by MCIN/AEI/10.13039/501100011033, and the European Union NextGenerationEU/PRTR and from Project No. PID2022-137845NB-C21, funded by MCIN/AEI/10.13039/501100011033 and by FEDER Una manera de hacer Europa. C.L. acknowledges financial support from Santander Bank and Public University of Navarra under resolution 2659/2021.

Finding scalable, cost-effective and environmentally safe solutions for Passive Daytime Radiative Cooling (PDRC) is essential for addressing energy and climate challenges. This study demonstrates the feasibility of achieving PDRC using only cement-based compounds, without the need for additional whitening agents or other additives. Unlike previous approaches that rely on external additives, the proposed solution leverages two fundamental cement phases—portlandite and tobermorite—offering a scalable and low-impact alternative. The research evaluates the radiative cooling potential of these phases, along with two widely used cements—white cement (WC) and ordinary Portland cement (OPC), by analyzing and comparing their homogenized complex permittivities, derived using the Kramers-Kronig (KK) method. Simulations were conducted to assess the cooling power over one year across three different climates using actual meteorological data. The portlandite exhibits positive Pcool, maintaining a temperature equal to or below the ambient temperature more than 90 % of the time in dry desert and warm temperate locations. Indoor controlled measurements results reveal that portlandite (CH) may exhibit temperatures 15 °C lower than OPC and 5 °C lower than WC., The research presented in this paper has been supported by funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 64450 (MIRACLE project, more information available at www.miracle-concrete.eu) from the EU Commission. Additionally, this work has received financial support from the projects TED2021-132074B-C31, TED2021-132074B-C32 and TED2021-132074B-C33, funded by MCIN/AEI/10.13039/ 501100011033, and the European Union NextGenerationEU/PRTR and from the projects PID2022-137845NB-C21, PID2022-137845NB-C22 funded by MCIN/AEI/10.13039/501100011033/and by FEDER Una manera de hacer Europa.