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
AuthorRamli, Khairun N.
SupervisorAbd-Alhameed, Raed A.
Excell, Peter S.
; Method of Moments; MoM
; Finite-Difference Time-Domain; FDTD
; Quasi-static method
; Hybrid computational method
; Principle of equivalent sources
Perfectly Matched Layer; PML
; Electromagnetic problems
The University of Bradford theses are licenced under a Creative Commons Licence.
InstitutionUniversity of Bradford
DepartmentSchool of Engineering, Design and Technology
MetadataShow full item record
AbstractThe main objective of this research is to model and analyse complex electromagnetic problems by means of a new hybridised computational technique combining the frequency domain Method of Moments (MoM), Finite-Difference Time-Domain (FDTD) method and a subgridded Finite-Difference Time-Domain (SGFDTD) method. This facilitates a significant advance in the ability to predict electromagnetic absorption in inhomogeneous, anisotropic and lossy dielectric materials irradiated by geometrically intricate sources. The Method of Moments modelling employed a two-dimensional electric surface patch integral formulation solved by independent linear basis function methods in the circumferential and axial directions of the antenna wires. A similar orthogonal basis function is used on the end surface and appropriate attachments with the wire surface are employed to satisfy the requirements of current continuity. The surface current distributions on structures which may include closely spaced parallel wires, such as dipoles, loops and helical antennas are computed. The results are found to be stable and showed good agreement with less comprehensive earlier work by others. The work also investigated the interaction between overhead high voltage transmission lines and underground utility pipelines using the FDTD technique for the whole structure, combined with a subgridding method at points of interest, particularly the pipeline. The induced fields above the pipeline are investigated and analysed. FDTD is based on the solution of Maxwell¿s equations in differential form. It is very useful for modelling complex, inhomogeneous structures. Problems arise when open-region geometries are modelled. However, the Perfectly Matched Layer (PML) concept has been employed to circumvent this difficulty. The establishment of edge elements has greatly improved the performance of this method and the computational burden due to huge numbers of time steps, in the order of tens of millions, has been eased to tens of thousands by employing quasi-static methods. This thesis also illustrates the principle of the equivalent surface boundary employed close to the antenna for MoM-FDTD-SGFDTD hybridisation. It depicts the advantage of using hybrid techniques due to their ability to analyse a system of multiple discrete regions by employing the principle of equivalent sources to excite the coupling surfaces. The method has been applied for modelling human body interaction with a short range RFID antenna to investigate and analyse the near field and far field radiation pattern for which the cumulative distribution function of antenna radiation efficiency is presented. The field distributions of the simulated structures show reasonable and stable results at 900 MHz. This method facilitates deeper investigation of the phenomena in the interaction between electromagnetic fields and human tissues.
Showing items related by title, author, creator and subject.
Method Development for the Application of Vibrational Spectroscopy to Complex Organic-Inorganic Materials in Astrobiology. A Systematic Development of Raman Spectroscopy and Related Analytical Methods to the Structural Chemistry at Organic (Biological) and Inorganic (Mineralogical) Interfaces of Material Assemblies Relevant to Astrobiology and Inter-Planetary Science.Scowen, Ian J.; Munshi, Tasnim; Whitaker, Darren A. (University of BradfordChemical and Forensic Sciences, 2015-07-08)In the search for the conformation of extant or extinct life in an extraterrestrial setting the detection of organic molecular species which may be considered diagnostic of life is a key objective. These molecular targets comprise a range of distinct chemical species, with recognisable spectroscopic features. This project aims to use these features to develop an in-situ molecular specific Raman spectroscopic methodology which can provide structural information about the organic–inorganic interface. The development of this methodology identified a surface enhanced Raman spectroscopic technique, that required minimal sample preparation, allowed for the detection of selected organic species immobilised on an inorganic matrix and was effective for quantities below those which conventional dispersive Raman spectroscopy would detect. For the first time spectral information was gained which allowed analysis of the organic–inorganic interface to be carried out, this gave an insight into the orientation with which molecules arrange on the surfaces of the matrices. Additionally a method for the detection of organic residues intercalated into the interlamellar space of smectite type clays was developed. An evaluation of the effectiveness of uni and multivariate methods for the analysis of large datasets containing a small number of organic features was also carried out, with a view to develop an unsupervised methodology capable of performing with minimal user interaction. It has been shown that a novel use of the Hotellings T2 test when applied to the principal component analysis of the datasets combined with SERS allows identification of a small number of organic features in an otherwise inorganic dominated dataset. Both the SERS and PCA methods hold relevance for the detection of organic residues within interplanetary exploration but may also be applied to terrestrial environmental chemistry.
A Comparative Analysis of Qualitative and Quantitative Research Methods and a Justification for Adopting Mixed Methods in Social Research.Haq, Muhibul (2015)The aim of this review is to create awareness about uses of available social research methods and to provide a guideline in adopting appropriate methods specifically in qualitative and mixed methods research genre. Based on the review of contemporary social research methods I believe that mixed methods research produces more accurate results than relying on either qualitative or quantitative methods alone in explaining complex social issues. This paper contributes to the methodological literature in two areas. First, create awareness among social researchers and students about the available research methods in order to help them to adopt suitable research designs in addressing their particular research questions. Second, encourage scholars from all disciplines to theorize further, especially in the field of mixed methods, and engage in a dialogue in order to improve methodological appropriateness for future research in social sciences.
Measurement of airborne sound insulation of timber noise barriers: Comparison of in-situ method CEN/TS 1793 with laboratory method EN1793-2Watts, Gregory R.; Morgan, P. (2009-07-13)Recent progress in the development of European standards has allowed the in situ testing of roadside noise barriers. CEN/TS 1793-5 describes a test method using maximum length sequences (MLS) for the characterisation of airborne sound insulation. However, many barriers are tested according to a laboratory standard, EN 1793-2, based on measurements carried out in reverberant chambers and in the case of timber barriers with a relatively low airborne sound insulation it is not clear to what extent the results of the two tests compare. The paper describes the results of tests carried out using both methods. Six samples of timber barrier were compared including single-leaf and double-leaf constructions and single-leaf constructions with an absorptive core. Very good agreement was found especially when account was taken of the valid frequency range in each test method. The results open up the possibility of routinely evaluating the performance of timber barriers at the roadside where build quality can be variable and there are concerns that the acoustic performance may not match that obtained under laboratory test conditions where typically the barrier is more carefully constructed.