Open Access
Terajets produced by dielectric cuboids
(AIP Publishing, 2014) Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Minin, Igor V.; Minin, Oleg V.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
The capability of generating terajets using three-dimensional (3D) dielectric cuboids working at terahertz (THZ) frequencies (as analogues of nanojets in the infrared band) is introduced and studied numerically. The focusing performance of the terajets is evaluated in terms of the transversal full width at half maximum (FWHM) along x- and y-directions using different refractive indices for a 3D dielectric cuboid with a fixed geometry, obtaining a quasi-symmetric terajet with a subwavelength resolution of 0.46 wavelengths when the refractive index is n=1.41. Moreover, the backscattering enhancement produced when metal particles are introduced in the terajet region is demonstrated for a 3D dielectric cuboid and compared with its two-dimensional (2D) counterpart. The results of the jet generated for the 3D case are experimentally validated at sub-THZ waves, demonstrating the ability to produce terajets using 3D cuboids.
Open Access
Lipid and protein oxidation marker compounds in horse meat determined by MIR spectroscopy
(MDPI, 2020) Jáuregui López, Irati; Zulategui Beñarán, Fernando; Beriain Apesteguía, María José; Sarriés Martínez, María Victoria; Beruete Díaz, Miguel; Insausti Barrenetxea, Kizkitza; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD
This work broadens the study of lipid and protein oxidation marker compounds in foal meat, employing the technology of Attenuated Total Reflectance-Fourier Transform Mid-Infrared Spectroscopy (ATR-FT/MIR, shortened in the following as MIR). As a main objective, marker compounds from 23 foals were extracted and their absorbance spectra were measured to establish prediction models (calibration and validation) between them and classical quantification analysis of the compounds. Another objective was to ascertain whether a previous extraction of the marker compounds before executing their MIR analysis is preferable compared to direct MIR measurements on the raw meat samples. In this context, marker compound results (TBARS between 0.4387 and 2.1040, and carbonyls between 4.07 and 4.68) showed more consistent predictive models than the ones achieved using quantitative analysis of the spectra obtained from the raw meat. Lipid oxidation compounds predictive models obtained in this work offered an R-cv(2) of 63.18% and protein oxidation R-cv(2) obtained in this project showed a value of 54.24%. Thus, MIR technology arises as a promising tool to identify and quantify products derived from lipid and protein oxidation in fresh foal meat.
Open Access
Ku band low profile asymmetric Bull’s-Eye antenna with reduced side lobes and monopole feeding
(IEEE, 2018) Beaskoetxea Gartzia, Unai; Torres García, Alicia E.; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In this paper, a linearly polarized low profile and asymmetric Bull’s-Eye leaky wave antenna fed by a monopole operating at 13 GHz is presented. Broadside radiation from the monopole is achieved by surrounding it with an asymmetric array of semicircular metallic strips on a grounded dielectric slab. With this implementation we demonstrate high gain with a weight of less than 80 g and lower side lobe levels compared to previous designs fed by a resonant slot. The measured antenna shows an experimental gain of 19.4 dBi with only 5 periods and a side lobe level of −16 dB (−20.3 dB for the numerical ideal case at f = 12.6 GHz), along with a narrow 6º beamwidth
Open Access
Millimeter-wave phase resonances in compound reflection gratings with subwavelength grooves
(Optical Society of America, 2010) Beruete Díaz, Miguel; Navarro Cía, Miguel; Skigin, Diana C.; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Experimental evidence of phase resonances in a dual-period reflection structure comprising three subwavelength grooves in each period is provided in the millimeter-wave regime. We have analyzed and measured the response of these structures and show that phase resonances are characterized by a minimum in the reflected response, as predicted by numerical calculations. It is also shown that under oblique incidence these structures exhibit additional phase resonances not present for normal illumination because of the potentially permitted odd field distribution. A satisfactory agreement between the experimental and numerical reflectance curves is obtained. These results confirm the recent theoretical predictions of phase resonances in reflection gratings in the millimeter-wave regime, and encourage research in this subject due to the multiple potential applications, such as frequency selective surfaces, backscattering reduction and complex-surface-wave-based sensing. In addition, it is underlined here that the response becomes much more complex than the mere infinite analysis when one considers finite periodic structures as in the real experiment.
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.
Embargo
Terahertz sensing based on metasurfaces
(Wiley, 2020) Beruete Díaz, Miguel; Jáuregui López, Irati; Institute of Smart Cities - ISC
The terahertz (THz) band has very attractive characteristics for sensing and biosensing applications, due to some interesting features such as being a non-ionizing radiation, very sensitive to weak interactions, thus, complementing typical spectroscopy systems in the infrared. However, a fundamental drawback is its relatively long wavelength (10–1000 µm) which makes it blind to small features, hindering seriously both thin-film and biological sensing. Recently, new ways to overcome this limitation have become possible thanks to the advent of metasurfaces. These artificial structures are planar screens usually made of periodic metallic resonators and whose electromagnetic response can be controlled at will by design. This design freedom allows metasurfaces to surpass the restrictions of classical THz spectroscopy, by creating fine details comparable to the size of the thin films or microorganisms under test. The strong field concentration near these small metasurface details at resonance makes them highly sensitive to tiny variations in the nearby environment, allowing for an enhanced detection more accurate than classical THz spectroscopy. The main advances in THz metasurface sensors from a historical as well as application-oriented perspective are summarized. The focus is put mainly on thin-film and biological sensors, with an aim to cover the most recent advances in the topic.
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.
Open Access
Blind spot mitigation in phased array antenna using metamaterials
(IEEE, 2014) Crépin, Thomas; Martel, Cédric; Gabard, Benjamin; Boust, Fabrice; Martinaud, Jean-Paul; Dousset, Thierry; Rodríguez Ulibarri, Pablo; Beruete Díaz, Miguel; Loecker, Claudius; Bertuch, Thomas; Marcotegui Iturmendi, José Antonio; Maci, Stefano; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this work, a metaradome based on a fakir’s bed of nails is designed and tested in order to suppress the blind directions of a 100-element antenna array. The antenna is a microstrip array designed to operate in X-band. The fakir’s bed metamaterial-like was first approximated using analytical formulas before a full-wave numerical optimization. Experimental results are exposed and confronted to numerical results. They show a significant reduction of the blind spot subsequent to the metaradome addition.
Open Access
Super-oscillatory metalens at terahertz for enhanced focusing with reduced side lobes
(MDPI, 2018) Legaria Lerga, Santiago; Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Institute of Smart Cities - ISC
In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, efficiency is optimized, compared to the conventional transparent–opaque zoning approach that introduces, inevitably, a high reflection in the opaque regions. Furthermore, a novel two-step optimization technique, based on evolutionary algorithms, is developed to reduce the side lobes and boost the intensity at the focus. After the design process, we demonstrate that the metalens is able to generate a focal spot of 0.46λ0 (1.4 times below the resolution limit) at the design focal length of 10λ0 with reduced side lobes (the side lobe level being approximately −11 dB). The metalens is optimized at 0.327 THz, and has been validated with numerical simulations.
Open Access
Wood zone plate fishnet metalens
(EDP Sciences, 2015) Orazbayev, Bakhtiyar; Beruete Díaz, Miguel; Navarro Cía, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Fresnel-zone plate lenses provide focusing performance while having low profile. Unfortunately, they usually display higher reflection losses than conventional dielectric lenses. Here, we demonstrate a low-profile Wood zone plate metalens based on the fishnet metamaterial working in a near-zero regime with an equivalent refractive index less than unity (nf = 0.51). The metalens is made of alternating dielectric and fishnet metamaterial concentric rings. The use of fishnet metamaterial allows reducing the reflections from the lens, while maintaining low profile, low cost and ease of manufacturing. The lens is designed towork at theW-band of the millimeter-waves range with a focal length FL = 22.8 mm (7.5 λ0) aiming at antenna or radar system applications. The focusing per- formance of the lens along with its radiation characteristics in a lens antenna configuration have been studied numerically and confirmed experimentally, showing a gain improvement of ~2.5 dB with respect to a fishnet Soret metalens.