Modelling Curved and Non-Aligned Surfaces using the Finite-Difference Time-Domain Method

The finite-difference time-domain (FDTD) method is widely used for computational electromagnetic simulations due to its efficiency and ease of implementation. However, due to its reliance on an orthogonal grid, it is difficult to represent curved and non-aligned planar surfaces. A common method of dealing with this is to use stair-cased meshes that align with the stair-cased grid as close as possible to the surface being meshed. This work explores the errors that arise from using stair-cased meshes of cavities for shielding and scattering problems. It is determined that the increased surface area of a stair-cased mesh alters the transmission and reflection of incident waves. A method of altering the boundary properties is presented to counteract the errors in transmission and reflection. This method is shown to reduce the error in the magnitude of shielding effectiveness (SE) of stair-cased cavities. However, as this method does not change the geometry of the mesh itself, errors in resonant frequency and the presence of spurious resonances is not affected. A second method is proposed to locally deform FDTD cells to conform to a curved or non-aligned planar surface. This method incorporates a thin layer model to vastly increase the efficiency of the algorithm when compared to bulk material alternatives. The method is shown to improve errors in the magnitude of SE, resonant frequency and spurious resonances when compared to stair-cased models

On the finite-difference modelling of electromagnetic problems in structured lattices

The thesis concentrates on the numerical analysis of electromagnetic fields with the finite difference method. Simple and fast approximative techniques are studied and developed for the estimation of the electromagnetic properties of various structures. Especially, techniques which preserve the simplicity of a structured lattice are explored. The emphasis in the thesis is put more into the rapid estimations than into the absolute accuracy of the studied parameters. Another goal is to give information about the characteristics of the studied structures: filters, dielectric mixtures and frequency selective surfaces. Filter structures are analysed with the finite-difference time-domain method. A simple trick is introduced to transform the curved shapes in a certain practical filter configuration into rectangular shapes to conform to the finite-difference computation lattice. Procedures which use finite difference methods to analyse dielectric mixtures are introduced. They are applied to calculate effective permittivities of two-phase random mixtures. The results are compared with theoretical mixing models with a conclusion that none of them agrees with the numerical results in the whole range of volume fraction. Therefore, a new empirical mixing model is created based on the numerical results. Polarisation transformation properties of frequency selective surfaces are also studied and some wide-band polariser structures are presented. It is shown how one-dimensional array models can give a good starting point for a two-dimensional array design.reviewe

Errors in the shielding effectiveness of cavities due to stair-cased meshing in FDTD: Application of empirical correction factors

The errors, due to stair-cased meshing, in the Shielding Effectiveness (SE) of cavities modelled with thin boundaries, in the Finite-Difference Time-Domain (FDTD) method, are examined. The errors in SE are found to be associated with the error in the surface area of the cavity caused by the use of a stair-cased mesh. An empirical solution is demonstrated, which improves the stair-cased model accuracy to be comparable to that achievable by a conformal model. Errors in the resonant frequencies ,Q factors and field minima of a cavity, due to the stair-cased mesh, are also noted

Performance of parallel FDTD method for shared- and distributed-memory architectures: Application tobioelectromagnetics

This work provides an in-depth computational performance study of the parallel finite-difference time-domain (FDTD) method. The parallelization is done at various levels including: shared- (OpenMP) and distributed- (MPI) memory paradigms and vectorization on three different architectures: Intel's Knights Landing, Skylake and ARM's Cavium ThunderX2. This study contributes to prove, in a systematic manner, the well-established claim within the Computational Electromagnetic community, that the main factor limiting FDTD performance, in realistic problems, is the memory bandwidth. Consequently a memory bandwidth threshold can be assessed depending on the problem size in order to attain optimal performance. Finally, the results of this study have been used to optimize the workload balancing of simulation of a bioelectromagnetic problem consisting in the exposure of a human model to a reverberation chamber-like environment

Performance of parallel FDTD method for shared- and distributed-memory architectures: Application tobioelectromagnetics

This work provides an in-depth computational performance study of the parallel finite-difference time-domain (FDTD) method. The parallelization is done at various levels including: shared- (OpenMP) and distributed- (MPI) memory paradigms and vectorization on three different architectures: Intel’s Knights Landing, Skylake and ARM’s Cavium ThunderX2. This study contributes to prove, in a systematic manner, the well-established claim within the Computational Electromagnetic community, that the main factor limiting FDTD performance, in realistic problems, is the memory bandwidth. Consequently a memory bandwidth threshold can be assessed depending on the problem size in order to attain optimal performance. Finally, the results of this study have been used to optimize the workload balancing of simulation of a bioelectromagnetic problem consisting in the exposure of a human model to a reverberation chamber-like environment

Efficient antenna modeling by DGTD

The work described in this article is partially funded by the Spanish National Projects TEC2013-48414-C3-01, CSD2008-00068, P09-TIC-5327, and P12-TIC-1442 and by the GENIL Excellence Network