Artículos (Electrónica y Electromagnetismo)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/10839

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Mostrando 1 - 20 de 504

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). España
The 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.
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 III
This 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.
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). España
Subdiffraction 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.
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 Republic
The 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.
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). España
Electronductive 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.
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 Andalucía
Isotropic 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.
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 Electromagnetismo
The 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.
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 Andalucía
In 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.
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 Andalucía
We 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.
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 Andalucía
Alternating 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.
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). España
This 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.
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). España
In 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.
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 España
We 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.
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. Bogotá
Babinet'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.
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 Electromagnetismo
It 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.
Faraday Waves under Perpendicular Electric Field and their Application to the Walking Droplet Phenomenon
(American Institute of Physics, 2021) Fernández Mateo, Raúl; Pérez Izquierdo, Alberto Tomás; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Junta de Andalucía
Vertically oscillating fluid surfaces have been a subject extensively studied in the past, as well as surface instabilities produced by electrohydrodynamic waves in similar configurations. In the present work, the unification of both effects and their consequences on the stability of the surface. Given the versatility of electromagnetic fields, application to the phenomenon of walking droplets is suggested; the dispersion relation and bouncing regimes of and the force on the droplets are revisited, and feasible experimental configurations are proposed.
Role of concentration-polarization electroosmosis in the dielectrophoresis of highly charged colloids: A theoretical study
(APS, 2025-05-16) Flores Mena, José Eladio; Fernández Mateo, Raúl; García Sánchez, Pablo; Ramos Reyes, Antonio; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; European Union (UE)
We analyze, both analytically and numerically, the electrokinetic behavior of highly charged dielectric microparticles suspended in aqueous electrolytes. Specifically, we consider small particles subjected to nonuniform AC electric fields and describe their motion as resulting from the interplay between electrical forces—dielectrophoresis (DEP)—and steady electroosmotic flows on the particle surface, a phenomenon known as concentration-polarization electroosmosis (CPEO). The net particle motion is known as dipolophoresis (DIP). We derive analytical expressions for the induced motion in the limit of small Dukhin numbers (i.e., relatively low surface conductance) and validate these results by comparing them with numerical simulations. This comparison confirms the reliability of our numerical approach, which we then extend to explore dipolophoresis for arbitrary Dukhin numbers. Our findings indicate that at low AC field frequencies, the contribution of CPEO to particle motion becomes significant for Dukhin numbers around 0.1 or higher, eventually surpassing the effect of DEP when the Dukhin number is on the order of one.
Quasi-static PEEC planar solver using a weighted combination of 2D and 3D analytical Green's functions and a predictive meshing generator
(Elsevier, 2018-09) Ahyoune, Saiyd; Sieiro, Javier; Carrasco, Tomás; Vidal, Neus; López-Villegas, José M.; Roca Moreno, Elisenda; Fernández Fernández, Francisco Vidal; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia e Innovación (MICIN). España
In this work, a quasi-static implementation of the partial element equivalent circuit (PEEC) method for the analysis of planar radiofrequency (RF) and microwave (uW) components is proposed. The procedure is divided in three parts. First, an alternative PEEC formulation based on energy concepts is described. Second, a smart mesh generator is developed in order to provide an accurate solution at minimum computational costs, taking into account both geometry and device physics as metrics for the correct sizing of mesh elements. And third, a weighted combination of the 2D and 3D quasi-static Green's functions (GF) is proposed for extending the valid frequency range of the quasi-static approximation. It is shown that the 3D-GF is very accurate at low frequency, whereas the 2D-GF is more suitable at higher frequencies. Numerical examples are compared to experimental data for different passive components and technologies in a wide frequency range
Enhanced systematic design of a voltage controlled oscillator using a two-step optimization methodology
(Elsevier, 2018-09) Moreira de Passos, Fabio; Martins R.; Lourenço N.; Roca Moreno, Elisenda; Póvoa R.; Canelas A.; Castro López, Rafael; Horta N.; Fernández Fernández, Francisco Vidal; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Economía y Competitividad (MINECO). España; Junta de Andalucía; Instituto de Telecomunicações; Fundação para a Ciência e Tecnologia
In this paper a design strategy based on bottom-up design methodologies is used in order to systematically design a voltage controlled oscillator. The methodology uses two computer-aided design tools: AIDA, a multi-objective multi-constraint circuit optimization tool, and SIDe-O, a tool that characterizes and optimizes integrated inductors with high accuracy (around 1% when compared to electromagnetic simulations). By using such tools, the difficult trade-offs inherent to radio-frequency circuits can be explored efficiently and accurately. Furthermore, with the capability that AIDA has at considering process parameter variations during the optimization, the resulting methodology is able to obtain truly robust circuit designs.
A novel design methodology for the mixed-domain optimization of a MEMS accelerometer
(Elsevier, 2018-06) Pak, Murat; Fernández Fernández, Francisco Vidal; Dundar, Gunhan; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo
This paper proposes a novel optimization-based design methodology that can be used for mixed-domain synthesis of MEMS accelerometers. Several problems have been identified with existing methodologies and comparative experiments that demonstrate the superiority of the proposed approach are performed. Highly accurate analytical models of the MEMS accelerometer have been used for the evaluation of the MEMS sensor performances in the mixed-domain optimization. The circuit level simulations, on the other hand, are based on an electrical simulator, e.g., Hspice. The implemented methodology has been tested on the optimization of a MEMS accelerometer that includes a capacitive MEMS sensor and an analog read-out circuitry.

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