Artículos (Electrónica y Electromagnetismo)
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Artículo Detailed Assessment of Hardware Implementations, Attacks and Countermeasures for the Ascon Authenticated Cipher(Wiley, 2025) Martín González, M.; Tena Sánchez, Erica; Potestad Ordóñez, Francisco Eugenio; Acosta Jiménez, Antonio José; Universidad de Sevilla. Departamento de Tecnología Electrónica; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia e Innovación (MICIN). España; European Union (UE). H2020; European Union (UE)The design and implementation of lightweight-oriented ciphers on hardware has turned into an urgent matter with the expansive field of Internet of Things (IoT) and the ever increasing presence of small electronic devices that require fast and secure communication in our modern world. In 2023, the Ascon cipher was selected as the new standard authenticated encryption with associated data (AEAD) algorithm for lightweight environments by the National Institute of Standards and Technology (NIST). This paper provides a full comparison and joint evaluation of the hardware implementations, attacks and countermeasures that have been proposed for Ascon since it was published, aiming to shed light on some open development paths in addition to enable the hardware designer to make better informed decisions. All in all, Ascon implementations tend to achieve great performance while staying lightweight, but unprotected implementations are vulnerable to hardware attacks, and some attacks can even dodge counter measures. The very promising Ascon cipher will surely thrive in the field of lightweight cryptography, but further work into the design of secure implementations is still needed, being this paper a great starting point for researchers and designers alike.Artículo Levitation? Yes, it is possible!(American Association of Physics Teachers, 2019-04-01) Pérez Izquierdo, Alberto Tomás; García Sánchez, Pablo; Sánchez Quintanilla, Miguel Angel; Fernández Prieto, Armando; Universidad de Sevilla. Departamento de Electrónica y ElectromagnetismoDuring July 2018, a group of top high school Spanish students attended a summer scientific camp at the University of Seville. The topic of the project was magnetic levitation. During the one-weeklong stay, the students investigated several possible ways of achieving stable levitation. These included diamagnetic levitation, use of superconductors, induced current levitation, and the toy LevitronVR . The experiments were accompanied by their corresponding conceptual and theoretical explanations.
Artículo Trapping of Micro- and Nanoparticles within Microfluidic Constrictions in AC Electric Fields(American Chemical Society, 2025) Fernández Mateo, Raúl; Gannoun Ep Khalifa, Rahma; Morgan, H.; Ramos Reyes, Antonio; García Sánchez, Pablo; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia e Innovación (MICIN). España; European Union (UE). H2020Trapping and separation of particles near microfluidic constrictions are efficiently achieved using electric fields. The phenomenon has been attributed to the dielectrophoretic (DEP) force arising from the nonhomogeneous electric field within the constrictions, which predicts particle trapping at or away from the constriction tip. In this work, we provide a more insightful description of the particle behavior around constrictions when subjected to ac electric fields. We demonstrate that, at low frequencies (below 10 kHz) and for solutions with conductivities lower than 0.1 S/m, new trapping positions close to the tips occur which cannot be explained using DEP forces only. We use the term extraordinary trapping position (ETP) to distinguish them from the trapping positions due to DEP. These trapping positions are explained when considering the action of, at least, two different phenomena: the hydrodynamic wall-repulsion induced by concentration-polarization electroosmosis (CPEO) on the particle surface and the fluid flow vortices due to CPEO on the constriction walls. Correctly interpreting these observations is crucial for experiments, such as those aiming to measure the electrical polarizability of proteins by trapping them in microfluidic constrictions.Artículo Monolithically-Integrated Bandpass Filters Using Capacitively-Loaded Intertwined Helical Resonators(Institute of Electrical and Electronics Engineers, 2025) Medrán Del Rio, José Luis; Fernández Prieto, Armando; Martel Villagrán, Jesús; Elmiger, Christian; Psychogiou, Dimitra; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Aplicada II; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Science Foundation Ireland (SFI); Ministerio de Educación. EspañaThis paper presents a novel compact 3D bandpass filter (BPF) concept based on new classes of intertwined helical resonators. The concept is demonstrated by three unique RF filter architectures: a second-order single-band BPF, a second-order dual-band BPF, and a differential single-band BPF. The filter designs are based on coupled-resonator theory, and their implementation is performed using stereolithography apparatus (SLA) 3D printing to create monolithic, screwless structures with ultra-low weight (20-65 gr) and minimal loss. The proposed intertwined helical resonator-based BPF concept, which enables designs with compact size and large fractional bandwidth (FBW) with transmission zeroes (TZ), has been experimentally validated. Manufactured prototypes have demonstrated the following RF performance: single-band BPF: center frequency of 1.08 GHz, 3 dB FBW of 15.5%, and insertion loss (IL) of 0.08 dB; dual-band BPF: passbands centered at 0.84 GHz and 1.53 GHz, with a 3 dB FBW of 19% and 6.5% and IL of 0.2 dB and 0.55 dB, respectively; differential single-band BPF: center frequency of 0.78 GHz, 3 dB FBW of 4%, and IL of 0.87 dB. To the best of the author's knowledge, this work is the first approach to 3D-printed differential BPFs.Artículo Efficient computation of the magnetic field created by a toroidal volumetric current of convex cross section with application to the study of the magnetic confinement in tokamaks(Elsevier, 2025-08) Camacho Aguilar, Miguel; Rodríguez Boix, Rafael; Cruz Zabala, Diego José; Galdón Quiroga, Joaquín; Ayllón Guerola, Juan Manuel; Viezzer, Eleonora; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; European Union (UE); European Research Council (ERC)In this paper we present an efficient approach for the numerical computation of the static vector potential and the poloidal magnetic field of a toroidal volumetric current with arbitrary convex cross section. The standard integral expressions for both the vector potential and the magnetic field include singularities that have a deleterious effect in the computation of these integrals. In order to handle these singularities, we first introduce a change of variables to polar coordinates with origin at the observation point that makes it possible to remove the singularities of the integrands thanks to the Jacobian factor. Then, two different numerical integration methods are applied to the resulting integrals: Ma-Rokhlin-Wandzura quadrature rules and the double exponential quadrature rule. Both methods efficiently handle the singularities in the derivative of the integrand for the integrals of the vector potential and the magnetic field, and the advantages and disadvantages of each method are discussed. The results obtained for the vector potential and magnetic field are validated by comparing with closed-form results existing for the vector potential and magnetic field of a circular loop and an infinite cylinder, and good agreement is found. Then, the magnetic field code is used to model the plasma toroidal current in a tokamak nuclear fusion reactor, and it is shown that the combined magnetic field of the plasma current and that of the poloidal and toroidal coils leads to magnetic confinement of the charged particles existing in the plasma.Artículo Magnetoinductive metasurface of capacitively-loaded split rings for local field homogenization in a 7 T MRI birdcage: A simulation study(Elsevier, 2023-12) Freire Rosales, Manuel José; Marqués Sillero, Ricardo; Tornero, Jesús; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia e Innovación (MICIN). EspañaThe transmit field B+ in a 7 T birdcage is inherently inhomogeneous due to the effects of wavelengths on tissue. This work investigates the homogenization of this field through metasurfaces that consist of a two-dimensional planar array of capacitively loaded conducting rings. The metasurfaces are placed in the intermediate space between the head and the birdcage on either side of the head. The periodical structure of this type of metasurface supports magnetoinductive waves because of the mutual inductive coupling existing between the elements of the array. The analysis takes advantage of this coupling and exploits the excitation of a standing magnetoinductive wave across the arrays, which creates a strong local field that contributes to locally homogenize the field of the birdcage. The presence of the arrays does not detune the birdcage, so that they can be used with commercial birdcages that operate both to transmit and to receive.Artículo Direct measurement of the electric field induced by a transcranial magnetic stimulator(Institute of Electrical and Electronics Engineers, 2023-05-15) Freire Rosales, Manuel José; Bernal Méndez, Joaquín; Gutiérrez-Muto, Ane Miren; Oliviero, Antonio; Tornero, Jesús; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Aplicada IIIThis work proposes a simple method to carry out in the laboratory a direct measurement of the primary solenoidal electric field that transcranial magnetic stimulation (TMS) coils generate in the brain. This method avoids indirect estimation of this electric field from measurements of magnetic fields and, at the same time, overcomes the difficulty posed by the presence of a dominant conservative electric field, also produced by the coil. This conservative electric field, which is removed in practice by human tissue, is eliminated in the proposed measurement method by using a simple setup that does not require the introduction of the measurement probe inside a conducting solution resembling the human tissue. The proposed measurement method allows for measuring the primary solenoidal electric field in front of the coil in the air. This method has been validated by comparing the results of electromagnetic simulation with the measurement of the magnetic field and the nonconservative electric field produced by a commercial TMS coil.Artículo Theory of Three-dimensional Subdiffraction Imaging(American Institute of Physics, 2006) Marqués Sillero, Ricardo; Freire Rosales, Manuel José; Baena, Juan D.; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Educación y Ciencia (MEC). EspañaSubdiffraction image formation and measurement are analyzed. It is shown that subdiffraction imaging devices cannot produce focusing of energy into three-dimensional spots of subdiffraction size. However, three-dimensional subdiffraction imaging is possible as a consequence of a matching/tunneling process. © 2006 American Institute of Physics.Artículo Electrically Small Isotropic Three-dimensional Magnetic Resonators for Metamaterial Design(American Institute of Physics, 2006) Baena, J. D.; Jelinek, L.; Marqués Sillero, Ricardo; Zehentner, J.; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Educación y Ciencia (MEC). España; Agency of Czech RepublicThe problem of the design of artificial magnetic resonators for isotropic metamaterials is addressed. The internal symmetries that ensure an isotropic behavior of such resonators are analyzed and some specific designs based on the proper arrangement of modified split ring resonators are proposed. These proposals are validated by electromagnetic simulations and experiments. The reported results are likely to have applications in the design of devices such as negative refractive index materials, superlenses, and metasurfaces with isotropic response.Artículo Electroinductive Waves in Chains of Complementary Metamaterial Elements(American Institute of Physics, 2006) Beruete, M.; Falcone, F.; Freire Rosales, Manuel José; Marqués Sillero, Ricardo; Baena, J. D.; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Educación y Ciencia (MEC). EspañaElectronductive waves supported by chains of resonators drilled on a metallic plate are presented. Propagation of energy comes as a consequence of the electric coupling between these resonators. Therefore, these waves are termed as electroinductive waves. They can be interpreted as the dual counterpart of the so-called magnetoinductive waves, which are due to the mutual inductances along chains of resonators. In order to show their existence, some electromagnetic simulations and experiments have been carried out, using as resonators the complementary particle of the split ring resonator. The reported result opens the way to a high variety of applications in one- and two-dimensional devices, such as transducers, delay lines, bends, power dividers, couplers, antennas, lenses, etc.Artículo Isotropic Frequency Selective Surfaces Made of Cubic Resonators(American Institute of Physics, 2007) Baena, J. D.; Jelinek, L.; Marqués Sillero, Ricardo; Mock, J. J.; Gollub, J.; Smith, D. R.; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Educación y Ciencia (MEC). España; Agencia de Proyectos de Investigación Avanzados de Defensa (DARPA). USA; Junta de AndalucíaIsotropic frequency selective surface (FSS) made of cubic arrangements of split ring resonators (SRRs) is proposed and analyzed. For this purpose, a suitable isotropic modification of the SRR was used in the design of a cubic unit element invariant under the tetrahedral point symmetry group. It was experimentally demonstrated that the transmission through such a FSS is angle and polarization independent. For comparison, another FSS, whose unit elements do not satisfy necessary symmetries, was measured, showing clearly anisotropic behavior. We feel then that symmetries play an important role. Potential device applications are envisioned for antenna technology at microwave and terahertz frequencies.Artículo Control of Two-phase Flow in a Microfluidic System Using ac Electric Fields(American Institute of Physics, 2007) Morgan, H.; Green, N. G.; Ramos Reyes, Antonio; García Sánchez, Pablo; Universidad de Sevilla. Departamento de Electrónica y ElectromagnetismoThe control and handling of fluids are central to many applications of the lab on chip. We report how alternating current (ac) electric fields can deflect and manipulate coflowing streams of two different electrolytes within a microfluidic channel. The two different electrolytes flow side by side over an array of interdigitated electrodes which occupies the width of the channel. Application of a 20 V (peak to peak) voltage at 1 MHz to the electrodes causes the liquid with higher conductivity to occupy a larger region of the channel. This effect causes a significant displacement of the boundary between the two fluids.Artículo Experimental Demonstration of a μ=-1 Metamaterial Lens for Magnetic Resonance Imaging(2008) Freire Rosales, Manuel José; Marqués Sillero, Ricardo; Jelinek, Lukas; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Educación y Ciencia (MEC). España; Junta de AndalucíaIn this work a μ=-1 metamaterial (MM) lens for magnetic resonance imaging (MRI) is demonstrated. MRI uses surface coils to detect the radio frequency (rf) energy absorbed and emitted by the nuclear spins in the imaged object. The proposed MM lens manipulates the rf field detected by these surface coils so that the coil sensitivity and spatial localization are substantially improved. Beyond this specific application, we feel that the reported results are the experimental confirmation of a new concept for the manipulation of rf field in MRI, which paves the way to many other interesting applications.Artículo Structural Tunability in Metamaterials(American Institute of Physics, 2009) Lapine, Mikhail; Powell, David A.; Gorkunov, Maxim V.; Shadrivov, Ilya V.; Marqués Sillero, Ricardo; Kivshar, Yuri S.; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Junta de AndalucíaWe propose an efficient approach for tuning the transmission characteristics of metamaterials through a continuous adjustment of the lattice structure and confirm it experimentally in the microwave range. The concept is rather general and applicable to various metamaterials as long as the effective medium description is valid. The demonstrated continuous tuning of a metamaterial response is highly desirable for a number of emerging applications of metamaterials, including sensors, filters, and switches, realizable in a wide frequency range.Artículo Microwave-induced Water Flows in Microsystems(American Institute of Physics, 2009) Ramos Reyes, Antonio; Robles, A.; García Sánchez, Pablo; Freire Rosales, Manuel José; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Gobierno de España; Junta de AndalucíaAlternating current electric fields are of increasing importance for the development of microfluidic pumps. We report how microwave fields can induce water flow in microsystems, irrespective of saline concentration. A drop of water is placed on two parallel coplanar microelectrodes that are energized by a microwave generator. Fluid flow is observed and the fluid velocity is about the same for two electrolytes with very different saline concentrations. Electrically induced gradients of temperature produce spatial variations in mass density and dielectric permittivity leading, respectively, to buoyancy and dielectric forces in the liquid. The observed fluid flow patterns demonstrate that both effects are taking place at different length scales: the dielectric forces dominate at lengths of the order of 100 μm or smaller, while buoyancy dominates around 1 mm.Artículo Nonlinear Split-ring Metamaterial Slabs for Magnetic Resonance Imaging(American Institute of Physics, 2011) López, Marcos A.; Freire Rosales, Manuel José; Algarín, José M.; Behr, Volker C.; Jakob, Peter M.; Marqués Sillero, Ricardo; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia e Innovación (MICIN). EspañaThis work analyzes the ability of split-ring metamaterial slabs with zero/high permeability to reject/confine the radiofrequency magnetic field in magnetic resonance imaging systems. Split-ring slabs are designed and fabricated to work in a 1.5 T system. Nonlinear elements consisting of pairs of crossed diodes are inserted in the split-rings, so that the slab permeability can be switched between a value close to unity when interacting with the strong field of the transmitting coil, and zero or high values when interacting with the weak field produced by protons in tissue. Experiments are shown where these slabs locally increase the signal-to-noise-ratio.Artículo Analysis of the Resolution of Split-ring Metamaterial Lenses with Application in Parallel Magnetic Resonance Imaging(American Institute of Physics, 2011) Algarín, José M.; Freire Rosales, Manuel José; López, Marcos A.; Lapine, Mikhail; Jakob, Peter M.; Behr, Volker C.; Marqués Sillero, Ricardo; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia e Innovación (MICIN). EspañaIn this work, we experimentally determine the resolution of split-ring metamaterials lenses with emphasis in magnetic resonance imaging applications. Two small sources are used to determine the minimal resolution of the lens, which is compared with previous theoretical predictions. Taking into account this minimal resolution, a second experiment is designed in order to study the ability of a split-ring lens to improve the localization of the field produced by two closely spaced coils. This ability could find application in parallel magnetic resonance imaging, which take advantage of the distinct coil sensitivities in order to reduce the image acquisition time.Artículo Self-assembly of Metal Nanowires Induced by Alternating Current Electric Fields(American Institute of Physics, 2015) García Sánchez, Pablo; Arcenegui Troya, Juan Jesús; Morgan, Hywel; Ramos Reyes, Antonio; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Junta de Andalucía; Gobierno de EspañaWe describe the reversible assembly of an aqueous suspension of metal nanowires into two different 2-dimensional stable configurations. The assembly is induced by an AC electric field of magnitude around 10 kV/m. It is known that single metal nanowires orientate parallel to the electric field for all values of applied frequency, according to two different mechanisms depending on the frequency. These different mechanisms also govern the mutual interaction between nanowires, which leads to directed-assembly into distinctive structures, the shape of which depends on the frequency of the applied field. We show that for frequencies higher than the typical frequency for charging the electrical double layer at the metal-electrolyte interface, dipole-dipole interaction leads to the formation of chains of nanowires. For lower frequencies, the nanowires form wavy bands perpendicular to the electric field direction. This behavior appears to be driven by the electroosmotic flow induced on the metal surface of the nanowires. Remarkably, no similar structures have been reported in previous studies of nanowires.Artículo Extension of Babinet's Principle for Plasmonic Metasurfaces(American Institute of Physics, 2021) Ortiz, J. D.; del Risco, J. P.; Baena, J. D.; Marqués Sillero, Ricardo; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia e Innovación (MICIN). España; Gobierno de Colombia; Universidad de San Buenaventura. BogotáBabinet's principle is widely applied in optics and has been useful for designing metasurfaces with dual behavior. Although this principle can be rigorously demonstrated for infinitely thin perfect conducting screens, it is not exact for any real screen. In fact, metals used in plasmonic metasurfaces are far from good conductors, and the thickness of samples is not negligible in comparison with the typical size of the patterned structure. In this paper, we propose an extension of Babinet's principle valid for plasmonic metasurfaces by redefining the concept of complementary screens and finding impedance relations between such screens that ultimately leads to a simple relation between the transmission matrices of two complementary plasmonic metasurfaces. The theory is valid under the assumptions of the electroquasistatic approximation and plane waves in the far field. It may find applications in the design of optical plasmonic metasurfaces, nanocircuits, and nanoantennas.Artículo Babinet's Principle and Saturation of the Resonance Frequency of Scaled-down Complementary Metasurfaces(American Institute of Physics, 2021) Ortiz, Julián D.; Baena, Juan D.; Marqués Sillero, Ricardo; Enemuo, Amarachukwu N.; Gollub, Jonah; Akhmechet, Roman; Penkov, Boyan; Sarantos, Chris; Crouse, David T.; Universidad de Sevilla. Departamento de Electrónica y ElectromagnetismoIt has been previously demonstrated that the resonant frequency of the Split Ring Resonator (SRR) reaches a saturation value when its size is continuously scaled down, and at the same time, the resonance is attenuated. Now, it is demonstrated that similar saturation and attenuation phenomena happens to its complementary screen, which is commonly called a Complementary SRR (CSRR). It was found that the saturation frequency of the CSRR is near the saturation frequency of the SRR with equal geometrical dimensions. It is possible to control their saturation levels by tuning the geometry of the resonators. This work is relevant for the design of quasi-optical metamaterials based on one or both kinds of structures (i.e., SRRs and CSRRs) at once, especially when they both are required to resonate at the same frequency.