Open Access
Perfect narrowband absorbers using simple lithography-free structures
(IEEE, 2024-10-08) Lezaun Capdevila, Carlos; Navajas Hernández, David; Liberal Olleta, Íñigo; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Light absorption is a key phenomenon for a variety of technologies [1]: radiative cooling, photovoltaics, sensing, communication and camouflaging are just a few examples. These applications demand scalable and compact devices that modulate their absorption spectra, usually engineered using cavities and/or periodic structures acting as resonators. Weak light matter interaction limits the absorption within ultra-compact devices, although epsilon-near-zero (ENZ) materials allows to greatly increase such interaction [2]. The lack of design standardization presents a big gap for designing absorbers. We present a thorough analysis of an arbitrary material on top of a PEC (perfect electric reflector) and a material separated by a spacer from the PEC. We overview the absorption phenomena for different permittivity regions, thicknesses, angles of incidence and polarization. This work helps standardize the design of these absorber configuration.
Open Access
Silicon carbide as a material-based high-impedance surface for enhanced absorption within ultra-thin metallic films
(Optical Society of America, 2020) Pérez Escudero, José Manuel; Buldain, Iban; Beruete Díaz, Miguel; Goicoechea Fernández, Javier; Liberal Olleta, Íñigo; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
The absorption of infrared radiation within ultra-thin metallic films is technologically relevant for different thermal engineering applications and optoelectronic devices, as well as for fundamental research on sub-nanometer and atomically-thin materials. However, the maximal attainable absorption within an ultra-thin metallic film is intrinsically limited by both its geometry and material properties. Here, we demonstrate that material-based high-impedance surfaces enhance the absorptivity of the films, potentially leading to perfect absorption for optimal resistive layers, and a fourfold enhancement for films at deep nanometer scales. Moreover, material-based high-impedance surfaces do not suffer from spatial dispersion and the geometrical restrictions of their metamaterial counterparts. We provide a proof-of-concept experimental demonstration by using titanium nanofilms on top of a silicon carbide substrate.
Open Access
Suppressed-scattering spectral windows for radiative cooling applications
(Optica, 2023) Pérez Escudero, José Manuel; Torres García, Alicia E.; Lezaun Capdevila, Carlos; Caggiano, Antonio; Peralta, Ignacio; Dolado, Jorge S.; Beruete Díaz, Miguel; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
The scattering of light by resonant nanoparticles is a key process for enhancing the solar reflectance in daylight radiative cooling. Here, we investigate the impact of material dispersion on the scattering performance of popular nanoparticles for radiative cooling applications. We show that, due to material dispersion, nanoparticles with a qualitatively similar response at visible frequencies exhibit fundamentally different scattering properties at infrared frequencies. It is found that dispersive nanoparticles exhibit suppressed-scattering windows, allowing for selective thermal emission within a highly reflective sample. The existence of suppressed-scattering windows solely depends on material dispersion, and they appear pinned to the same wavelength even in random composite materials and periodic metasurfaces. Finally, we investigate calcium-silicate-hydrate (CSH), the main phase of concrete, as an example of a dispersive host, illustrating that the co-design of nanoparticles and host allows for tuning of the suppressed-scattering windows. Our results indicate that controlled nanoporosities would enable concrete with daylight passive radiative cooling capabilities.
Open Access
Nanoparticle derived suppressed-scattering bands for radiative cooling
(IEEE, 2023) Lezaun Capdevila, Carlos; Pérez Escudero, José Manuel; Torres García, Alicia E.; Caggiano, Antonio; Peralta, Ignacio; Dolado, Jorge S.; Liberal Olleta, Íñigo; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Light scattering using resonant nanoparticles is crucial for improving sun irradiance reflection in a daytime radiative cooler. Popular nanoparticles in radiative cooling literature are analyzed in terms of scattering performance due to material dispersion. Different scattering properties in the infrared range have been detected while a similar behavior can be achieved in the solar range due to changes in material dispersion. Also, suppressed scattering windows are produced by dispersive nanoparticles, allowing high reflectance while enabling thermal emission selectively. Material dispersion alone produces such scattering windows, thus, given a material, they will always remain in the same region regardless geometry and location of particles. Lastly, calcium silicate hydrate (CSH), the main phase of concrete, is studied as a dispersive host example. These results demonstrate the importance of a co-design between host and nanoparticles dispersion for daytime radiative cooling and that nanoporosities design are a key ingredient that could allow concrete-based daytime radiative coolers.
Open Access
Multiple absorption regimes in simple lithography-free structures leading to ultrathin slabs
(2024-07-08) Lezaun Capdevila, Carlos; Navajas Hernández, David; Liberal Olleta, Íñigo; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
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.
Open Access
Radiative cooling properties of portlandite and tobermorite: two cementitious minerals of great relevance in concrete science and technology
(American Chemical Society, 2023-06-23) Dolado, Jorge S.; Goracci, Guido; Arrese-Igor, Silvia; Ayuela, Andrés; Torres Betancourt, Angie Tatiana; Liberal Olleta, Íñigo; Beruete Díaz, Miguel; Gaitero, Juan J.; Cagnoni, Matteo; Cappelluti, Federica; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Although concrete and cement-based materials are the most engineered materials employed by mankind, their potential for use in daytime radiative cooling applications has yet to be fully explored. Due to its complex structure, which is composed of multiple phases and textural details, fine-tuning of concrete is impossible without first analyzing its most important ingredients. Here, the radiative cooling properties of Portlandite (Ca(OH)2) and Tobermorite (Ca5Si6O16(OH)2·4H2O) are studied due to their crucial relevance in cement and concrete science and technology. Our findings demonstrate that, in contrast to concrete (which is a strong infrared emitter but a poor sun reflector), both Portlandite and Tobermorite exhibit good radiative cooling capabilities. These results provide solid evidence that, with the correct optimization of composition and porosity, concrete can be transformed into a material suitable for daytime radiative cooling.
Open Access
Enhancing the infrared and visible emission properties of calcium silicate hydrate for radiative cooling using metamaterials
(IEEE, 2022) Lezaun Capdevila, Carlos; Dolado, Jorge S.; Torres García, Alicia E.; Pérez Escudero, José Manuel; Liberal Olleta, Íñigo; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Two periodic structures composed of metal cylinders with different orientations are used to improve the solar reflection of calcium silicate hydrate (CSH) while maintaining its atmospheric emission. Interesting effects have been found when the distance between bars is small, suggesting that lattice effects, arising from the interaction between the rods could be leveraged in the design of these metamaterials. The size of the metal bars is selected based on state of the art micro-manufacturing techniques. This study limits its scope to a CSH gel model; i.e. the most important component of cement-based materials. Further research will be undertaken to consider a best description of the dielectric function of concrete.
Open Access
Lithography-free perfect narrowband absorbers using simple layered structures
(IEEE, 2024-10-08) Lezaun Capdevila, Carlos; Navajas Hernández, David; Liberal Olleta, Íñigo; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Light absorbers are key components for multiple applications ranging from heat and energy management to communications and sensing. This work explores different complex permittivity combinations for material-reflector and material-spacer-reflector configurations, achieving perfect absorption under different permittivity regimes and thicknesses. Using silicon carbide, we discuss polarization and angle dependencies, and the potential of exploiting different permittivity regimes within a device for multi-band absorption. This work helps standardize absorber design and offer insights to engineer perfect absorbers for applications such as thermal emission, absorption, communication and sensing.