Modelling and analysis of complex electromagnetic problems using FDTD subgridding in hybrid computational methods. Development of hybridised Method of Moments, Finite-Difference Time-Domain method and subgridded Finite-Difference Time-Domain method for precise computation of electromagnetic interaction with arbitrarily complex geometries.

摘要

The main objective of this research is to model and analyse complex electromagnetic problemsudby means of a new hybridised computational technique combining the frequency domainudMethod of Moments (MoM), Finite-Difference Time-Domain (FDTD) method and a subgriddedudFinite-Difference Time-Domain (SGFDTD) method. This facilitates a significant advance in theudability to predict electromagnetic absorption in inhomogeneous, anisotropic and lossy dielectricudmaterials irradiated by geometrically intricate sources. The Method of Moments modellingudemployed a two-dimensional electric surface patch integral formulation solved by independentudlinear basis function methods in the circumferential and axial directions of the antenna wires. Audsimilar orthogonal basis function is used on the end surface and appropriate attachments withudthe wire surface are employed to satisfy the requirements of current continuity. The surfaceudcurrent distributions on structures which may include closely spaced parallel wires, such asuddipoles, loops and helical antennas are computed. The results are found to be stable and showedudgood agreement with less comprehensive earlier work by others.udThe work also investigated the interaction between overhead high voltage transmission lines andudunderground utility pipelines using the FDTD technique for the whole structure, combined withuda subgridding method at points of interest, particularly the pipeline. The induced fields aboveudthe pipeline are investigated and analysed.udFDTD is based on the solution of Maxwell¿s equations in differential form. It is very useful forudmodelling complex, inhomogeneous structures. Problems arise when open-region geometriesudare modelled. However, the Perfectly Matched Layer (PML) concept has been employed toudcircumvent this difficulty. The establishment of edge elements has greatly improved theudperformance of this method and the computational burden due to huge numbers of time steps, inudthe order of tens of millions, has been eased to tens of thousands by employing quasi-staticudmethods.udThis thesis also illustrates the principle of the equivalent surface boundary employed close toudthe antenna for MoM-FDTD-SGFDTD hybridisation. It depicts the advantage of using hybridudtechniques due to their ability to analyse a system of multiple discrete regions by employing theudprinciple of equivalent sources to excite the coupling surfaces. The method has been applied forudmodelling human body interaction with a short range RFID antenna to investigate and analyseudthe near field and far field radiation pattern for which the cumulative distribution function ofudantenna radiation efficiency is presented. The field distributions of the simulated structuresudshow reasonable and stable results at 900 MHz. This method facilitates deeper investigation ofudthe phenomena in the interaction between electromagnetic fields and human tissues.