Contribution to the quality improvement of the antenna measurement using post-processing techniques = Contribución a la mejora de la calidad de medida de antena usando técnicas de post-procesado

One important task in the design of an antenna is to carry out an analysis to find out the characteristics of the antenna that best fulfills the specifications fixed by the application. After that, a prototype is manufactured and the next stage in design process is to check if the radiation pattern differs from the designed one. Besides the radiation pattern, other radiation parameters like directivity, gain, impedance, beamwidth, efficiency, polarization, etc. must be also evaluated. For this purpose, accurate antenna measurement techniques are needed in order to know exactly the actual electromagnetic behavior of the antenna under test. Due to this fact, most of the measurements are performed in anechoic chambers, which are closed areas, normally shielded, covered by electromagnetic absorbing material, that simulate free space propagation conditions, due to the absorption of the radiation absorbing material. Moreover, these facilities can be employed independently of the weather conditions and allow measurements free from interferences. Despite all the advantages of the anechoic chambers, the results obtained both from far-field measurements and near-field measurements are inevitably affected by errors. Thus, the main objective of this Thesis is to propose algorithms to improve the quality of the results obtained in antenna measurements by using post-processing techniques and without requiring additional measurements. First, a deep revision work of the state of the art has been made in order to give a general vision of the possibilities to characterize or to reduce the effects of errors in antenna measurements. Later, new methods to reduce the unwanted effects of four of the most commons errors in antenna measurements are described and theoretical and numerically validated. The basis of all them is the same, to perform a transformation from the measurement surface to another domain where there is enough information to easily remove the contribution of the errors. The four errors analyzed are noise, reflections, truncation errors and leakage and the tools used to suppress them are mainly source reconstruction techniques, spatial and modal filtering and iterative algorithms to extrapolate functions. Therefore, the main idea of all the methods is to modify the classical near-field-to-far-field transformations by including additional steps with which errors can be greatly suppressed. Moreover, the proposed methods are not computationally complex and, because they are applied in post-processing, additional measurements are not required. The noise is the most widely studied error in this Thesis, proposing a total of three alternatives to filter out an important noise contribution before obtaining the far-field pattern. The first one is based on a modal filtering. The second alternative uses a source reconstruction technique to obtain the extreme near-field where it is possible to apply a spatial filtering. The last one is to back-propagate the measured field to a surface with the same geometry than the measurement surface but closer to the AUT and then to apply also a spatial filtering. All the alternatives are analyzed in the three most common near-field systems, including comprehensive noise statistical analyses in order to deduce the signal-to-noise ratio improvement achieved in each case. The method to suppress reflections in antenna measurements is also based on a source reconstruction technique and the main idea is to reconstruct the field over a surface larger than the antenna aperture in order to be able to identify and later suppress the virtual sources related to the reflective waves. The truncation error presents in the results obtained from planar, cylindrical and partial spherical near-field measurements is the third error analyzed in this Thesis. The method to reduce this error is based on an iterative algorithm to extrapolate the reliable region of the far-field pattern from the knowledge of the field distribution on the AUT plane. The proper termination point of this iterative algorithm as well as other critical aspects of the method are also studied. The last part of this work is dedicated to the detection and suppression of the two most common leakage sources in antenna measurements. A first method tries to estimate the leakage bias constant added by the receiver’s quadrature detector to every near-field data and then suppress its effect on the far-field pattern. The second method can be divided into two parts; the first one to find the position of the faulty component that radiates or receives unwanted radiation, making easier its identification within the measurement environment and its later substitution; and the second part of this method is able to computationally remove the leakage effect without requiring the substitution of the faulty component. Resumen Una tarea importante en el diseño de una antena es llevar a cabo un análisis para averiguar las características de la antena que mejor cumple las especificaciones fijadas por la aplicación. Después de esto, se fabrica un prototipo de la antena y el siguiente paso en el proceso de diseño es comprobar si el patrón de radiación difiere del diseñado. Además del patrón de radiación, otros parámetros de radiación como la directividad, la ganancia, impedancia, ancho de haz, eficiencia, polarización, etc. deben ser también evaluados. Para lograr este propósito, se necesitan técnicas de medida de antenas muy precisas con el fin de saber exactamente el comportamiento electromagnético real de la antena bajo prueba. Debido a esto, la mayoría de las medidas se realizan en cámaras anecoicas, que son áreas cerradas, normalmente revestidas, cubiertas con material absorbente electromagnético. Además, estas instalaciones se pueden emplear independientemente de las condiciones climatológicas y permiten realizar medidas libres de interferencias. A pesar de todas las ventajas de las cámaras anecoicas, los resultados obtenidos tanto en medidas en campo lejano como en medidas en campo próximo están inevitablemente afectados por errores. Así, el principal objetivo de esta Tesis es proponer algoritmos para mejorar la calidad de los resultados obtenidos en medida de antenas mediante el uso de técnicas de post-procesado. Primeramente, se ha realizado un profundo trabajo de revisión del estado del arte con el fin de dar una visión general de las posibilidades para caracterizar o reducir los efectos de errores en medida de antenas. Después, se han descrito y validado tanto teórica como numéricamente nuevos métodos para reducir el efecto indeseado de cuatro de los errores más comunes en medida de antenas. La base de todos ellos es la misma, realizar una transformación de la superficie de medida a otro dominio donde hay suficiente información para eliminar fácilmente la contribución de los errores. Los cuatro errores analizados son ruido, reflexiones, errores de truncamiento y leakage y las herramientas usadas para suprimirlos son principalmente técnicas de reconstrucción de fuentes, filtrado espacial y modal y algoritmos iterativos para extrapolar funciones. Por lo tanto, la principal idea de todos los métodos es modificar las transformaciones clásicas de campo cercano a campo lejano incluyendo pasos adicionales con los que los errores pueden ser enormemente suprimidos. Además, los métodos propuestos no son computacionalmente complejos y dado que se aplican en post-procesado, no se necesitan medidas adicionales. El ruido es el error más ampliamente estudiado en esta Tesis, proponiéndose un total de tres alternativas para filtrar una importante contribución de ruido antes de obtener el patrón de campo lejano. La primera está basada en un filtrado modal. La segunda alternativa usa una técnica de reconstrucción de fuentes para obtener el campo sobre el plano de la antena donde es posible aplicar un filtrado espacial. La última es propagar el campo medido a una superficie con la misma geometría que la superficie de medida pero más próxima a la antena y luego aplicar también un filtrado espacial. Todas las alternativas han sido analizadas en los sistemas de campo próximos más comunes, incluyendo detallados análisis estadísticos del ruido con el fin de deducir la mejora de la relación señal a ruido lograda en cada caso. El método para suprimir reflexiones en medida de antenas está también basado en una técnica de reconstrucción de fuentes y la principal idea es reconstruir el campo sobre una superficie mayor que la apertura de la antena con el fin de ser capaces de identificar y después suprimir fuentes virtuales relacionadas con las ondas reflejadas. El error de truncamiento que aparece en los resultados obtenidos a partir de medidas en un plano, cilindro o en la porción de una esfera es el tercer error analizado en esta Tesis. El método para reducir este error está basado en un algoritmo iterativo para extrapolar la región fiable del patrón de campo lejano a partir de información de la distribución del campo sobre el plano de la antena. Además, se ha estudiado el punto apropiado de terminación de este algoritmo iterativo así como otros aspectos críticos del método. La última parte de este trabajo está dedicado a la detección y supresión de dos de las fuentes de leakage más comunes en medida de antenas. El primer método intenta realizar una estimación de la constante de fuga del leakage añadido por el detector en cuadratura del receptor a todos los datos en campo próximo y después suprimir su efecto en el patrón de campo lejano. El segundo método se puede dividir en dos partes; la primera de ellas para encontrar la posición de elementos defectuosos que radian o reciben radiación indeseada, haciendo más fácil su identificación dentro del entorno de medida y su posterior substitución. La segunda parte del método es capaz de eliminar computacionalmente el efector del leakage sin necesidad de la substitución del elemento defectuoso.

Influence of the Second Flexural Mode on the Response of High-Speed Bridges

This paper deals with the assessment of the contribution of the second flexural mode to the dynamic behaviour of simply supported railway bridges. Alluding to the works of other authors, it is suggested in some references that the dynamic behaviour of simply supported bridges could be adequately represented taking into account only the contribution of the fundamental flexural mode. On the other hand, the European Rail Research Institute (ERRI) proposes that the second mode should also be included whenever the associated natural frequency is lower than 30 Hz]. This investigation endeavours to clarify the question as much as possible by establishing whether the maximum response of the bridge, in terms of displacements, accelerations and bending moments, can be computed accurately not taking account of the contribution of the second mode. To this end, a dimensionless formulation of the equations of motion of a simply supported beam traversed by a series of equally spaced moving loads is presented. This formulation brings to light the fundamental parameters governing the behaviour of the beam: damping ratio, dimensionless speed $ \alpha$=VT/L, and L/d ratio (L stands for the span of the beam, V for the speed of the train, T represents the fundamental period of the bridge and d symbolises the distance between consecutive loads). Assuming a damping ratio equal to 1%, which is a usual value for prestressed high-speed bridges, a parametric analysis is conducted over realistic ranges of values of $ \alpha$ and L/d. The results can be extended to any simply supported bridge subjected to a train of equally spaced loads in virtue of the so-called Similarity Formulae. The validity of these formulae can be derived from the dimensionless formulation mentioned above. In the parametric analysis the maximum response of the bridge is obtained for one thousand values of speed that cover the range from the fourth resonance of the first mode to the first resonance of the second mode. The response at twenty-one different locations along the span of the beam is compared in order to decide if the maximum can be accurately computed with the sole contribution of the fundamental mode.

Involutivity of the Hamilton-Cartan equations of a second-order Lagrangian admitting a first-order Hamiltonian formalism

Involutivity of the Hamilton-Cartan equations of a second-order Lagrangian admitting a first-order Hamiltonian formalism

Effect of strain and magnetic field on the critical current and electric resistance of the joints between HTS coated conductors

Engineering of devices and systems such as magnets, fault current limiters or cables, based on High Temperature Superconducting wires requires a deep characterization of the possible degradation of their properties by handling at room temperature as well as during the service life thus establishing the limits for building up functional devices and systems. In the present work we report our study regarding the mechanical behavior of spliced joints between commercial HTS coated conductors based on YBCO at room temperature and service temperature, 77 K. Tensile tests under axial stress and the evolution of the critical current and the electric resistance of the joints have been measured. The complete strain contour for the tape and the joint has been obtained by using Digital Image Correlation. Also, tensile tests under external magnetic field have been performed and the effect of the applied field on the critical current and the electric resistance of the joints has been studied. Finally, a preliminary numerical study by means of Finite Element Method (FEM) of the mechanical behavior of the joints between commercial HTS is presented.

Effect of strain and magnetic field on the critical current and electric resistance of the joints between HTS coated conductors

Engineering of devices and systems such as magnets, fault current limiters or cables, based on High Temperature Superconducting wires requires a deep characterization of the possible degradation of their properties by handling at room temperature as well as during the service life thus establishing the limits for building up functional devices and systems. In the present work we report our study regarding the mechanical behavior of spliced joints between commercial HTS coated conductors based on YBCO at room temperature and service temperature, 77 K. Tensile tests under axial stress and the evolution of the critical current and the electric resistance of the joints have been measured. The complete strain contour for the tape and the joints has been obtained by using Digital Image Correlation. Also, tensile tests under external magnetic field have been performed and the effect of the applied field on the critical current and the electric resistance of the joints has been studied. Additionally, fatigue tests under constant cyclic stress and loading-unloading ramps have been carried out in order to evaluate the electromechanical behavior of the joints and the effect of maximum applied stress on the critical current. Finally, a preliminary numerical study by means of the Finite Element Method (FEM) of the electromechanical behavior of the joints between commercial HTS is presented.

Urbanism and dictatorship: perspectives of the field of urban studies

In 1933 public letter to Wilhelm Furtwängler, Joseph Goebbels synthesized the official understanding of the link between politics, art and society in the early steps of the Third Reich. By assuming the ethos of art, politics acquired a plastic agency to mold its objects —population and the state— as a unified entity in the form of a ‘national-popular community’ (Volksgemeinschaft); in turn, by infusing art with a political valence, it became part of a wider governmental apparatus that reshaped aesthetic discourses and practices. Similar remarks could be made about the ordering of cities and territories in this period. Dictatorial imaginations mobilized urbanism —including urban theory, urban design and planning— as a fundamental tool for social organization. Under their aegis the production of space became a moment in a wider production of society. Many authors suggest that this political-spatial nexus is intrinsic to modernity itself, beyond dictatorial regimes. In this light, I propose to use dictatorial urbanisms as an analytical opportunity to delve into some concealed features of modern urban design and planning. This chapter explores some of these aspects from a theoretical standpoint, focusing on the development of dictatorial planning mentalities and spatial rationalities and drawing links to other historical episodes in order to inscribe the former in a broader genealogy of urbanism. Needless to say, I don’t suggest that we use dictatorships as mere templates to understand modern productions of space. Instead, these cases provide a crude version of some fundamental drives in the operationalization of urbanism as an instrument of social regulation, showing how far the modern imagination of sociospatial orderings can go. Dictatorial urbanisms constituted a set of experiences where many dreams and aspirations of modern planning went to die. But not, as the conventional account would have it, because the former were the antithesis of the latter, but rather because they worked as the excess of a particular orientation of modern spatial governmentalities — namely, their focus on calculation, social engineering and disciplinary spatialities, and their attempt to subsume a wide range of everyday practices under institutional structuration by means of spatial mediations. In my opinion the interest of dictatorial urbanisms lies in their role as key regulatory episodes in a longer history of our urban present. They stand as a threshold between the advent of planning in the late 19th and early 20th century, and its final consolidation as a crucial state instrument after World War II. We need, therefore, to pay attention to these experiences vis-à-vis the alleged ‘normal’ development of the field in contemporary democratic countries in order to develop a full comprehension thereof.

The Theory and Practice of Restoration in England in the Second Half of the 19th Century: The Work of George E. Street

Análisis de la teoría y práctica de la restauración en Inglaterra en la segunda mitad del siglo XIX, enfocada al trabajo realizado por el arquitecto George Edmund Street, desde el punto de vista de su investigación sobre la historia de la construcción de la arquitectura gótica en Europa.

Educational Needs and Future Prospects in the Field of Health and Safety at Work in Spain

Aiming to identify educational needs to promote employment in the field of Occupational Health and Safety in Spain, this paper analyses the matching degree between the existing university educational offer and the professional demand. Results indicate that the new official Masters are well driven but, at graduate level, a broad range of topics regarding occupational hazards should be promoted and the scope of cross subjects should be expanded. New profiles that are emerging within this field are also identified.