Using genetic algorithms for compensating the local magnetic perturbation of a ship in the earth's magnetic field

This paper shows a practical application of genetic algo- rithms (GAs) for compensating the local magnetic perturbation produced by a ship, while moving in the earth's magnetic field. The compensation is achieved by modifying the number of turns and the current magnitude across the so-called degaussing coils distributed along the ship. A GA scheme for automatic optimisation of these parameters is used. A new objective-function strategy, called a boundary method, is proposed. It is shown that the convergence of the GA is greatly improved when the new objective function is used. Different selection mechanisms, objective function strategies, and scaled methods are revised in this paper. The results show that GAs can be efficiently used to reduce drastically the magnetic field levels of real practical ships

On the Influence of Spatial Dispersion on the Performance of Graphene-Based Plasmonic Devices

We investigate the effect of spatial dispersion phenomenon on the performance of graphene-based plasmonic devices at THz. For this purpose, two different components, namely a phase shifter and a low-pass filter, are taken from the literature, implemented in different graphene-based host waveguides, and analyzed as a function of the surrounding media. In the analysis, graphene conductivity is modeled first using the Kubo formalism and then employing a full-$k_\rho$ model which accurately takes into account spatial dispersion. Our study demonstrates that spatial dispersion up-shifts the frequency response of the devices, limits their maximum tunable range, and degrades their frequency response. Importantly, the influence of this phenomenon significantly increases with higher permittivity values of the surrounding media, which is related to the large impact of spatial dispersion in very slow waves. These results confirm the necessity of accurately assessing non-local effects in the development of practical plasmonic THz devices.Comment: 5 pages, 18 figures, 2 table

Impulse-Regime Analysis of Novel Optically-Inspired Phenomena at Microwaves

In this chapter, we present recent advances based on Fourier transformation techniques to model dispersive UWB phenomena and far-field radiation from complex CRLH structures. Section 2 first employs inverse Fourier transforms to study pulse propagation along this type of medium. Then, a Fourier transform approach is applied to the current which flows along the CRLH line, accurately retrieving the time-domain far-field radiation of the structure [which behaves as a leaky-wave antenna, (LWA)]. The main advantages of the proposed techniques are the easy treatment of complex CRLH structures, a deep insight into the physics of the phenomena, and an accurate and a fast computation, which avoids the time-consuming analysis required by completely numerical simulations.Ecole Polytechnique de Montrea

Formal Expression of Sensitivity and Energy Relationship in the Context of the Coupling Matrix

International audiencePrecise formulas to express the formal relationship between the time average stored energy in the resonators of a low-pass filter network and the sensitivity of the reflection S -parameter with respect to the coupling matrix terms are demonstrated in this paper, considering the normalized frequency axis. These relationships are found in the modern context of the N+2 coupling matrix, and for both diagonal and general nondiagonal coupling elements of the matrix. The results are valid for any type of coupling topology represented by the N+2 coupling matrix. Different examples are included as validation. Furthermore, important implications and applications derived from the new relationships are highlighted

An Efficient Technique to Assess the Convergence of the Multimode Equivalent Network for Waveguide Devices

[EN] Numerical methods are widely used to analyze and design microwave components for communication applications.In the implementation of any numerical technique, however, there are always a set of parameters that must be properly adjusted in order to obtain, at the same time, computational efficiency and numerical accuracy of the results. In this context, therefore, we focus in this paper on the multimode equivalent network formulation for waveguide devices, and we propose a more intuitive and efficient strategy for choosing these parameters. Following our approach, setting only one global numerical variable is sufficient to adjust automatically the specific convergence parameters of each discontinuity to give a specific level of numerical accuracy of the results. As a consequence, the computational efficiency is significantly increased. In addition, the user experience is significantly improved since our approach eliminates all lengthy convergence tests previously needed to assure good numerical accuracy. In addition to theory, we discuss in this paper a number of numerical results that clearly demonstrate how the new strategy is very effective, thereby fully validating the theoretical formulation.This work was supported in part by the Spanish Government through the Ministerio de Educacion, Cultura y Deporte under Grant FPU15/02883, in part by the Ministerio de Economia y Competitividad through the sub-projects 4 and 1 of the coordinated project under Grant TEC2016-75934-C4-R, and in part by the Fundacion Seneca de la Region de Murcia under Grant 19494/PI/14 and Grant 20147/EE/17.Gomez Molina, C.; Quesada Pereira, F.; Alvarez Melcon, A.; Boria Esbert, VE.; Guglielmi, M. (2018). An Efficient Technique to Assess the Convergence of the Multimode Equivalent Network for Waveguide Devices. IEEE Transactions on Microwave Theory and Techniques. 66(2):651-659. https://doi.org/10.1109/TMTT.2017.2785837S65165966

Predicción de la sensibilidad ante tolerancias de fabricación en un filtro guía-onda butterworth

En este artículo se presenta un método nuevo para la predicción de la sensibilidad en filtros Butterworth pasobanda formados por cavidades acopladas. La sensibilidad del parámetro de reflexión respecto a variaciones en los coeficientes de acoplo se calcula en el prototipo pasobajo. A partir de este valor, es posible predecir el máximo error que se producirá en el parámetro de reflexión en el peor de los escenarios posibles. Además, se propone una aplicación práctica de la relación existente entre la sensibilidad y la energía almacenada en estructuras formadas por resonadores acoplados, permitiendo predecir la sensibilidad de un filtro Butterworth en línea utilizando únicamente el retardo de grupo. El nuevo método se ha validado en un filtro Butterworth de orden 6, que ha sido diseñado a modo de ejemplo.Martínez Mendoza, M.; Gómez Díaz, JS.; Lorente, JA.; Alvarez Melcon, A. (2011). Predicción de la sensibilidad ante tolerancias de fabricación en un filtro guía-onda butterworth. 2011 IV Jornadas de Introducción a la Investigación de la UPCT. 1(4):85-87. http://hdl.handle.net/10251/33714S85871

Efficient Calculation of the 3-D Rectangular Waveguide Green’s Functions Derivatives by the Ewald Method

In this contribution, the Ewald method has efficiently been applied to accelerate the computation of the rectangular waveguide Green’s functions derivatives. Based on previous works, we have outlined new approximation formulae that avoid the evaluation of computationally expensive complementary error functions of complex argument, needed by the Ewald method. This is possible when the internal medium of the rectangular waveguide is homogeneous and lossless. On the other hand, different convergence numerical studies have been carried out, showing a similar convergence rate for computing the original Green’s functions and their derivatives. Moreover, we have checked that the computational time is only slightly increased for obtaining the derivatives as compared to the original Green’s functions, after the application of these new techniques. The new derived expressions are useful for the evaluation of electromagnetic fields, the characterization of dielectric materials and step discontinuities between rectangular waveguides, and the analysis of rectangular cavities using integral equation formulations. For validation, the electric field produced by a surface electric current density with a rectangular pulse distribution has been evaluated, using the new proposed expressions. These results have been compared to simulations provided by a full-wave finite elements commercial software to verify their correctness, exhibiting a good agreement