Luis Diaz Angulo

FDTD Modeling of Graphene Devices Using Complex Conjugate Dispersion Material Model

Graphene-based devices constitute a pioneering field of research for their extraordinary electromagnetic properties. The incorporation of appropriate models into numerical simulators is necessary in order to take advantage of these properties. In this work, we propose a method to incorporate graphene-sheet models into the FDTD method. The use of vector-fitting techniques expands the permittivity of graphene into a rational function series of complex conjugate pole-residue pairs, which is implemented into FDTD by an auxiliary differential equation formulation. Simple waveguiding problems validate our approach.

Source and Boundary Implementation in Vector and Scalar DGTD

We summarize the boundary and source implementation for the several formulations of the discontinuous Galerkin time domain method (DGTD). Since DGTD with zeroth-order scalar basis functions using the upwind flux, coincides with the finite volume time domain (FVTD), many of the concepts developed for FVTD can be ported to DGTD in any of its different formulations (scalar/vector basis, upwind/centered flux). Numerical examples illustrate the different alternatives.

A Spurious-Free Discontinuous Galerkin Time-Domain Method for the Accurate Modeling of Microwave Filters

The simulation of highly resonant structures requires techniques that are accurate and free of spurious-mode contamination. Spurious modes can severely corrupt the solution of a physical problem, and their suppression is a must for any numerical scheme in the frequency or in the time domain (TD). In this paper, we present the application of a highly accurate spurious-free vector discontinuous Galerkin TD method to waveguide applications. We show that spurious solutions (which increase with the number of degrees of freedom of the problem) can be efficiently attenuated by using penalized fluxes. For validation, we apply our approach to the simulation of microwave filters since their highly resonant behavior is challenging for TD techniques.

3-D Discontinuous Galerkin Time-Domain Method for Anisotropic Materials

Discontinuous Galerkin, applied to time-dependent Maxwell equations (DGTD), offers attractive properties when compared to other numerical methods. This method is flexible and accurate, like the finite element method, and efficient as well as scalable like finite-difference time-domain algorithms. In this letter, a new rigorous treatment of anisotropic materials in three dimensions is described and validated for the upwind-flux DGTD method.

A DIVERGENCE-FREE BEM METHOD TO MODEL QUASI-STATIC CURRENTS: APPLICATION TO MRI COIL DESIGN

The modeling of quasi-static optimization problems often involves divergence-free surface current densities. In this paper, a novel technique to implement these currents by using the boundary element method framework is presented. A locally-based characterization of the current density is employed, to render a fully geometry-independent formulation, so that it can be applied to arbitrary shapes. To illustrate the versatility of this approach, we employ it for the design of gradient coils for MRI, providing a solid mathematical framework for this type of problem. 1. INTRODUCTION Many problems in engineering require to determine the spatial distribution of electric currents ∞owing in a conductive surface which satisfles given requirements for the flelds, electromagnetic energy, etc. they produce. The reconstruction of current distribution on the conducting surface subjected to these constraints can be seen as an inverse problem. An appropriate and realistic formulation of this type of problems is presented in this paper, by incorporating a suitable model of the current under search, in terms of the stream function, into the Boundary Element Method (BEM). The use of stream function for the characterization of surface current densities has been widely employed (1). The BEM has been proved to be an excellent tool in the solution of electromagnetic problems (2,3); and the incorporation of the stream function into a numerical computational technique, such us BEM, has also been already considered for the solution of electromagnetic inverse

A Leap-Frog Discontinuous Galerkin Time-Domain Method for HIRF Assessment

In this paper, we demonstrate the computational affordability and accuracy of a leap-frog discontinuous Galerkin (LFDG) time-domain method for high intensity radiated fields assessment in electromagnetic compatibility for aerospace. The conformal truncation of the computational domain is discussed and formulated in the LFDG context. Numerical validations are performed on challenging test cases, in comparison to measurements and to other numerical methods, demonstrating the accuracy, efficiency, and scalability of the algorithm.

Improving the SAR Distribution in Petri-Dish Cell Cultures

Petri dishes of different types are widely used in bioelectromagnetic experiments for the assessment of the non-thermal biological effects of electromagnetic radiation. Two important qualities required for the experimental setups are to guarantee a sufficiently high level of exposure and to maintain uniformity of the fields affecting the cell culture under study. In this paper, we apply two novel techniques to improve both parameters: the use of dishes with an elliptical shape and the addition of metallic patches underneath the Petri dish. Results for plane-wave illumination at 2.5 GHz are shown. This methodology can also be extended to Petri dishes inside waveguide applicators.

On the Design of Aircraft Electrical Structure Networks

As part of the technology research engaged in the EU Clean Sky 1 project, we present in this paper an electrical structure network (ESN) designed to prevent the impact on an electronic equipment of unwanted voltage drops appearing when nonmetal composite materials are used for grounding. An iterative process has been followed to reach an optimal tradeoff solution meeting all the aircraft requirements: structural, safety, low weight, electrical, etc. Guidelines on the design of a low-impedance metal ESN, to minimize the inductive behavior of the power distribution network, are outlined in this paper. To this end, we employ the UGRFDTD simulation tool, combining finite-difference time domain to analyze the general EM problem, and a multiconductor transmission-line network to handle internal coupling between cables running along coinciding routes. The capability of this tool to create time-domain snapshots of surface currents is shown to provide a useful way to optimize the ESN, thanks to the insight gained on the physics of the problem.

An Analysis of the Leap-Frog Discontinuous Galerkin Method for Maxwell's Equations

In this paper, we explore the accuracy limits of a finite-element time-domain (TD) method applied to the Maxwell equations, based on a discontinuous Galerkin scheme in space, and a leap-frog temporal integration. The dispersion and dissipation properties of the method are investigated, as well as the anisotropy of the errors. The results of this novel analysis are represented in a practical and comprehensible manner, useful for the application of the method, and for the understanding of the behavior of the errors in discontinuous Gelerkin TD methods. A comparison with the finite-difference TD method, in terms of computational cost, is also included.

A Hybrid Crank–Nicolson FDTD Subgridding Boundary Condition for Lossy Thin-Layer Modeling

The inclusion of thin lossy material layers, such as carbon-based composites, is essential for many practical applications for modeling the propagation of electromagnetic energy through composite structures such as those found in vehicles and electronic equipment enclosures. Many existing schemes suffer problems of late time instability, inaccuracy at low frequency (LF), and/or large computational costs. This paper presents a novel technique for the modeling of thin-layer lossy materials in finite-difference time domain (FDTD) schemes, which overcomes the instability problem at low computational cost. For this, a 1-D subgrid is used for the spatial discretization of the thin-layer material. To overcome the additional time-step constraint posed by the reduction in the spatial cell size, a Crank–Nicolson time-integration scheme is used locally in the subgridded zone, and hybridized with the usual 3-D Yee-FDTD method, which is used for the rest of the computational domain. Several numerical experiments demonstrating the accuracy of this approach are shown and discussed. Results comparing the proposed technique with classical alternatives based on impedance boundary condition approaches are also presented. The new technique is shown to have better accuracy at LFs and late time stability than existing techniques with low computational cost.