Electromagnetic Waves

This volume is based on the contributions of several authors in electromagnetic waves propagations. Several issues are considered. The contents of most of the chapters are highlighting non classic presentation of wave propagation and interaction with matters. This volume bridges the gap between physics and engineering in these issues. Each chapter keeps the author notation that the reader should be aware of as he reads from chapter to the other

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

The 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.Ministry of Higher Education Malaysia and Universiti Tun Hussein Onn Malaysia (UTHM

HIGH EFFICIENCY AXIAL DIFFRACTION OUTPUT SCHEMES FOR THE A6 RELATIVISTIC MAGNETRON

High-power microwave research strives for compact and highly efficient vacuum diode-driven sources. MAGIC particle-in-cell (PIC) computer simulations have shown that the performance of the well-known A6 relativistic magnetron with radial power extraction through one or more of its cavities can be improved by instead using axial power extraction through a mode-converting horn antenna, resulting in improved efficiency (30% improved to 70%) and greater output power handling capability (sub-gigawatt improved to multi-gigawatt) without breakdown. In addition, axial extraction results in a more compact profile that is compatible with mounting permanent magnets, which eliminate the need for bulky pulsed electromagnets or cryo-magnets and greatly enhance system efficiency. To this end, a variety of technologies were simulated and tested in experiment, the latter which required the design, construction, testing, and calibration of new diagnostics, pulsed power systems, and hardware, such as the complex A6 magnetron with diffraction output horn antenna (MDO). The primary goal of the experiments was to verify simulated 70% efficiency and greater than 1 GW of output power from the MDO. A less expensive vii compact MDO\u27 variant, essentially an A6 magnetron with a flat-plate mode converter and \u03c0-mode strap was also simulated. Although both the MDO and the compact MDO are compatible with permanent magnets fitted around their exteriors, an effective configuration was simulated for the compact MDO, promising reduced size and increased efficiency of the total microwave system. In addition, both versions of the MDO were susceptible to bombardment of leakage electrons on their output windows; cathode endcaps were developed and tested to mitigate this issue. Finally, to further improve output power, a rodded metamaterial-like cathode that showed improved power in other relativistic magnetrons was also considered by simulation in an A6 magnetron with radial extraction.\u2

DIAGONAL AND OFF-DIAGONAL MAGNETO-IMPEDANCE IN FERROMAGNETIC MICROWIRES AND THIN FILMS

The discovery of the giant magneto-impedance (GMI) effect in 1994 had a strong impact on the development of micro magnetic sensors. In certain soft magnetic materials, such as composites of amorphous thin wires, the magneto-impedance change (MI ratio) is in the range of 50-100% in the MHz frequency band for external magnetic fields of few Oe. Special thin-film structures have been proposed to provide the MI effect in miniature elements. In the present work, the concept of the magneto-impedance matrix has been elaborated, which enables the explanation of variety of MI field characteristics in wires and films from the common point of view. The fabrication technologies of the narrow thin film MI samples with different structures also were developed, including layered films and films integrated with a helical planar microcoil. The experimental technique employed in the work allowed us to measure all components of the total magneto-impedance matrix that came as the first verification of the matrix concept of the magneto-impedance. Different methods of getting the asymmetrical and antisymmetrical magneto-impedance behaviours were proposed demonstrating a great success of the impedance matrix concept. In the case of a simple transverse magnetic anisotropy, the diagonal components of the magneto-impedance matrix are symmetric and the off-diagonal components are antisymmetrical with respect to the de longitudinal magnetic field. The asymmetry in MI behaviour can be related to either a certain asymmetric arrangement of the dc magnetic configuration or a contribution to the measured voltage due to the ac cross-magnetisation process, represented by the off-diagonal component. The first case is realised in the wire and film having the helical or crossed anisotropies respectively, which are subjected to an ac current superposed with a de bias current. In the other approach, the asymmetric voltage response can be obtained by applying the ac current in series through the MI element (wire or film) and the small coil surrounded it. No helical anisotropy is required in this case. These kinds of asymmetrical MI are especially important for developing auto-biased linear MI sensors. The thin film with the integrated planar microcoil allowed us to measure the off-diagonal impedance in the sandwiched film. Results obtained for MI in thin films open up the perspective directions for the integrated MI sensors. The applications of the MI effect are not limited only by magnetic sensor technology. In this work, a new type of tuneable composite materials was proposed, the effective microwave permittivity (dielectric constant) of which depends on the de external magnetic field applied to the composite as a whole. The composite consists of the short pieces of ferromagnetic wires embedded into a dielectric matrix. The composite sample can be fabricated in the form of thin slab with thickness less than 1 millimetre. The short wire inclusions play the role of "the elementary scatterers", when the electromagnetic wave irradiates the composite and induces an electrical dipole moment in each inclusion. These induced dipole moments form the dipole response of the composite, which can be characterised by some effective permittivity. The field dependence of the effective permittivity arises from a high field sensitivity of the ac surface impedance of a ferromagnetic wire. In the vicinity of the antenna resonance (related with the short wire inclusions) any variations in the magneto-impedance of wires result in large changes of the effective permittivity. Therefore, this composite demonstrates both the tuneable and resonance properties (selective absorption). Thus, we have demonstrated a possibility of using the MI effect to design field-controlled composites and band-gap structures. A number of applications can be proposed, including selective microwave coatings with the field-dependent reflection/transmission coefficients and selective tuneable waveguides where the composite material may be used as an additional field-dependent coating. In addition, in the final chapter of future work we will take a quick look at tuneable composites with other microstructures and methods of the excitation

Generalized averaged Gaussian quadrature and applications

A simple numerical method for constructing the optimal generalized averaged Gaussian quadrature formulas will be presented. These formulas exist in many cases in which real positive GaussKronrod formulas do not exist, and can be used as an adequate alternative in order to estimate the error of a Gaussian rule. We also investigate the conditions under which the optimal averaged Gaussian quadrature formulas and their truncated variants are internal

MS FT-2-2 7 Orthogonal polynomials and quadrature: Theory, computation, and applications

Quadrature rules find many applications in science and engineering. Their analysis is a classical area of applied mathematics and continues to attract considerable attention. This seminar brings together speakers with expertise in a large variety of quadrature rules. It is the aim of the seminar to provide an overview of recent developments in the analysis of quadrature rules. The computation of error estimates and novel applications also are described