Optimizing the magnetoinductive lens: Improvement, limits, and possible applications

In this contribution, the basic concepts underlying the physics of magnetoinductive MI lenses are developed and the main practical limitations to their performances are analyzed. Strategies to overcome such limitations are proposed. Possible applications of MI lenses in magnetic resonance imaging are discussed.Ministerio de Ciencia y Educación de España-TEC2004-04249-C02-02Junta de Andalucía-P06-TIC-0136

Structure and architectural project: two examples with masonry walls.

International Conference on Structures and Architecture(1ª.2010.Guimarães, Portugal)[Abstract] The paper presents two buildings solved with masonry walls: a family house in Betanzos and a multi-storey apartment building located at Lugo. The structure of the first one is solved by load-bearing walls of precast concrete blocks that arise from an elevated floor slab. The concrete block, though hidden, provides housing modulating, simplifying the tasks of construction, the wholeness of the building as well as guarantees other physical properties (fire resistance, thermal inertia, sound insulation). The second building is a residential building, which has four floors (the fourth one under the roof) built on a small site. There is a real ‘tour de force’ in this building project whose load-bearing walls of brickwork (perforated klinker) solve both structural requirement and thermal insulation of the façade with a reduced thickness. Through these examples, we offer an overview of various aspects relating to the materialization of the architectur

Use of Mutual Coupling to Decrease Parasitic Inductance of Shunt Capacitor Filters

In this paper, we propose and study several new designs of a shunt capacitor filter with two surface-mount technology capacitors. These designs make use of mutual inductance effects to increase the attenuation provided by the filter in the range of high frequencies where the filter behaves inductively. We provide lumped element circuitmodels for the proposed designs that allow identification of the key inductive parameters that determine the high-frequency performance of these filters. We obtain the equa- tions relating these parameters to the effective inductance of the filter, which can be used to compare the high-frequency behavior of different filter designs. We have fabricated and measured several compact shunt capacitor filters with improved performance at high frequencies. We have found that, compared with a shunt capacitor filter with one capacitor, a proper filter design with two capacitors can easily increase in 15–20 dB the high-frequency attenuation provided by the filter. This design also outperforms by 10–15 dB a traditional shunt capacitor filter with two capacitors closely placed. Moreover, this improvement is obtained with no increase in size, cost, or time of design of the filter.Ministerio de Economía Y Competitividad TEC2014-54097-

Accurate modeling of split ring metamaterial lenses for magnetic resonance imaging applications

The usefulness of thin split ring metamaterial slabs for imaging applications, including magnetic resonance imaging applications, has attracted some attention in the past years. However, the small number of unit cells across these thin slabs prevents the direct application of continuous medium models for its characterization. The main aim of this contribution is to provide a rigorous model for these structures, also clarifying the usefulness of continuous medium approach for their characterization. The proposed model is a generalization of the classical Lorentz procedure to two dimensions and is able to deal with electrically thin slabs made of small resonant closed current loops. The obtained results are validated by full-wave electromagnetic simulations and compared with the continuous model approximation of the slab.Ministerio de Educación y Ciencia de España-TEC2007-68013-C02-01/TCM y CSD2008-00066Junta de Andalucía-P06-TIC-0136

Full-wave analysis of the excitation of magnetostatic-surface waves by a semi-infinite microstrip transducer - Theory and experiment

This paper presents a new method for the complete characterization of the radiation of magnetostatic-surface waves in microstrip transmission lines with longitudinal magnetization. This method is based on the analysis of the excitation of leaky modes in microstrip lines and provides both the propagation constant and the complex impedance of the microstrip. From these quantities, the radiation resistance and other relevant characteristics of the line can be directly obtained

Insertion loss of magnetostatic-surface wave transducers - Transmission-line model and experiment

In this paper, a transmission-line model is developed for the computation of the insertion loss of magnetostatic-surface wave transducers and measurements are carried out by the authors to check this model. In a first step of the analysis, closed-form expressions for the solution of the telegrapher's equations for the two microstrip transducers are obtained. The insertion loss is then derived from this solution as a function of three transmission-line parameters, i.e., the propagation constant and the characteristic impedance of the YIG-loaded microstrip line and the mutual inductance between the two microstrips, these quantities being, in general, complex. In a second step, these transmission-line parameters are numerically computed by applying a full-wave method-of-moments technique. Thus, the theoretical results obtained are found to be in good agreement with experimental results

Realistic metamaterial lenses: Limitations imposed by discrete structure

We study the peculiarities of a metamaterial "superlens," caused by its discrete structure and finite size. We show that precise modeling of the lens provides remarkable distinctions from continuous medium approximation. In particular, we address the problem of highest resolution that can be achieved with a realistic electrically thin metamaterial lens. We conclude that discrete structure imposes essential limitations on the resolution and that the resolution cannot be improved by decreasing dissipation in the system. Further implications related to effective medium description of discrete structures are discussed.Ministerio de Educación y Ciencia TEC2007-65376 y TEC2007-68013-C02- 01Unión Europea FEDER CSD2008-00066Junta de Andalucía TIC-25

Signal-to-noise ratio evaluation in resonant ring metamaterial lenses for MRI applications

In this paper, we present a method for the evaluation of the signalto- noise ratio in magnetic resonance imaging (MRI) coils loaded with resonant ring metamaterial lenses, in the presence of a conducting phantom resembling human tissue. The method accounts for the effects of the discrete and finite structure of the metamaterial. Numerical computations are validated with experimental results, including laboratory measurements and MRI experiments.Ministerio de Ciencia e Innovación CSD2008-00066 y TEC2010- 16948Junta de Andalucía TIC-0623

Characteristics of aperture coupled microstrip antennas on magnetized ferrite substrates

The method of moments in the spectral domain is applied to the full-wave analysis of aperture coupled microstrip antennas in the case where the substrate of the antennas is a layered medium containing magnetized ferrites. The subsectional basis functions used in the analysis make it possible to handle patch antennas and coupling apertures with right angle corners of arbitrary shape. The numerical results obtained show that antennas on ferrite substrates fed by single microstrip lines can radiate both circular and linear polarization, the polarization state being dependent on the orientation of the ferrites bias magnetic field. For a given polarization state, the matching frequency band of the antennas can be tuned over a wide frequency range by adjusting the magnitude of the bias magnetic field. Also, the polarization state can be continuously tuned from circular to linear within the same frequency band by adjusting both the magnitude and the orientation of the bias magnetic field. Some measurements are presented in order to check the validity of the numerical algorithm developed

Three-dimensional superresolution in metamaterial slab lenses: Experiment and theory

This paper presents a theoretical and experimental study on the viability of obtaining two- and three-dimensional superresolution (i.e., resolution overcoming the diffraction limit for all directions in space) by means of metamaterial slab lenses. Although the source field cannot be actually reproduced at the back side of the lens with superresolution in all space directions, the matching capabilities of metamaterial slabs does make possible the detection of images with three-dimensional superresolution. This imaging takes place because of the coupling between the evanescent space harmonic components of the field generated at both the source and the detectorMinisterio de Educación y Ciencia TEC2004- 04249-C02-0