A fractal model for the lightning induced current on a transmission line

This article presents a model of a tortuous lightning channel, and a study of the consequent electromagnetic coupling to a transmission line. We analyse the fractal dimension of the induced current on the line, compared with the fractal dimension of the lightning channel and the impinging electromagnetic field on the line. This comparison confirms our previous studies pointing out that the channel fractal dimension and the electromagnetic field fractal dimension are related (in particular, for typical lightning parameters they are the same). A comparison of simulated fields and line currents with experimental measurements is also attempte

Lightning radiation field due to channel tortuosity and branching

The effect of lightning channel branching on the temporal waveform of the radiated fields of the return stroke is modeled. The effect of branching is isolated, and compared to the effect of tortuosity of an unbranched channe

Improved-Accuracy Source Reconstructionon Arbitrary 3-D Surfaces

This paper presents a novel formulation of the source reconstruction problem on arbitrary three-dimensional (3-D) surfaces based on integral equations. Rigorous boundary integral field identities are employed to enforce that the two unknown currents are Maxwellian on the reconstruction surface; this leads to a dual integral-equation formulation, in contrast to the single-equation formulation found in literature. Numerical tests against reference currents allow a quantitative assessment of the improvements in accuracy afforded by the novel formulation, with important benefits in diagnostic application

Prediction of radiated electromagnetic emissions from PCB traces based on Green dyadics

Because it costs to solve ElectroMagnetic Compatibility (EMC) problems late in the development process, new methods have to predict radiated electromagnetic emissions at the design stage. In the case of complex printed Circuit Boards (PCBs) containing embedded microstrips and a large number of nets, a tradeoff between accuracy and simulation time must be found for this evaluation. In this paper the basic algorithm used within a new emissions predictive analysis tool: ElectroMagnetic Interferences Radiated (EMIR) is presented. It is able to take accurately into account the actual cross section between the metal plane and the air for each PCB trace. It is compared to theoretical formulas for validation. The effects of superstrate (cover) on a dipole radiation are describe

Hierarchical bases for non-hierarchic 3Dtriangular meshes

We describe a novel basis of hierarchical, multiscale functions that are linear combinations of standard Rao-Wilton- Glisson (RWG) functions. When the basis is used for discretizing the electric field integral equation (EFIE) for PEC objects it gives rise to a linear system immune from low-frequency breakdown, and well conditioned for dense meshes. The proposed scheme can be applied to any mesh with triangular facets, and therefore it can be used as if it were an algebraic preconditioner. The properties of the new system are confirmed by numerical results that show fast convergence rates of iterative solvers, significantly better than those for the loop-tree basis. As a byproduct of the basis generation, a generalization of the RWG functions to nonsimplex cells is introduced

A finite element approach to inverse scattering problems

En este proyecto se desarrolla una aplicación basada en "Microwave Imaging" (MWI), implementada con el propósito de obtener las propiedades materiales desconocidas de un determinado objeto. Este método consta de dos partes fundamentales: El Problema Directo y el Algoritmo Inverso. La primera etapa, el Problema Directo, implica la medición del campo eléctrico disperso a lo largo de un dominio material. El Objeto de Interés (OI) representa un cuerpo material desconocido que se encuentra dentro de un tanque, rodeado por un conjunto de antenas que iluminan el escenario y almacenan los datos experimentales de las mediciones relacionadas con el campo eléctrico. Además, se introduce un medio adaptador dentro del recinto cerrado, el cual es denominado como "background". Con el objetivo de simular los datos experimentales, se desarrolla el Método de los Elementos Finitos. FEM representa una técnica matemática e ingenieril muy potente que nos permite resolver un conjunto de ecuaciones lineales que describen el comportamiento electromagnético. De este modo, podremos generar los datos sintéticos referidos a las variables nodales, que definen el escenario de imagen simulado mediante un simulador de FEM, denominado GiD y desarrollado por la UPC. Después de resolver el Problema Directo, se aborda el "Contrast Source Inversion Method" (CSIM) con el propósito de reconstruir los parámetros físicos originales que definen el OI. Haciendo uso de este algoritmo de inversión será viable alcanzar el error mínimo global entre los datos reales y los reconstruidos. Cuando este método iterativo converja, los resultados reconstruidos serán analizados con el objeto de identificar los materiales implicados en el "Imaging Domain". En este trabajo se describen los diferentes experimentos relacionados con el Problema Directo y Algoritmo Inverso, obteniendo diversas conclusiones sobre el funcionamiento de FEM-CSIM. En concreto, se analizan los conductores eléctricos perfectos, la distribución de las fuentes de corriente, las própiedades dieléctricas del "background" y la influencia de la frecuencia. Del mismo modo, los resultados de reconstrucción serán comparados en diferentes experimentos, obteniendo información sobre la resolución del método y las limitaciones del algoritmo. Finalmente es importante destacar las simulaciones realizadas con medios con y sín pérdidas, y los experimentos de biomedicina que tratan de representar posibles experimentos reales de imagen médica. Observaremos como CSIM proporciona una calidad alta en los resultados cómo para poder detectar la posicion y características de los objetivos. En las mejores situaciones de reconstrucción obtendremos errores en torno al 25%, que aunque puedan parecer discretos, son suficientes en muchas aplicaciones de imagen médica

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Adaptive Weighting Scheme for Multi-Objective Optimization in Metasurface Antenna Design

We present a novel adaptive weighting scheme suited to the current-based optimization of metasurface antennas. The problem is formulated in terms of a weighted sum of individual objective functions corresponding to different constraints. A nonlinear conjugate gradient optimization algorithm is combined with an hyperplane adaptive weighting scheme to improve the convergence properties. The proposed approach is inspired by a geometrical interpretation of the properties of the Pareto front, and guarantees a balancing of the individual goals. The procedure has been applied to the design of broadside-radiating metasurface antenna working at 23 GHz, and demonstrated its effectiveness in improving both the speed of convergence and quality of the solution with respect to existing algorithms

Human-vs Machine Design of Antennas: Evolution Behavior in Genetic Shape Optimization

Random-based global optimization algorithms have found extensive application in the domain of antenna shape design, especially when conventional solutions relying on human expertise are lacking. In this research contribution, we investigate the performance of random-based global optimization in scenarios where the design problem could otherwise be tackled through conventional human-guided design methods and parameter adjustments driven by simulations. The present case study involves shape optimization of a 2D pixelated domain, performed via binary coding and a Genetic Algorithm (GA). The reference geometry is a square resonant patch-type antenna with optimized probe feeding position. The initial domain is a pin-centered rectangle larger than the patch itself, so that the optimizer is eventually free to indirectly find the best pin position corresponding to the best design of the patch