The aim of this study is to analysis, investigate and find out the solutions for the problems associated with the implementations of antennas RFID Reader and Tag for various applications. In particular, the efficiency of the RFID reader antenna and the detection range of the RFID tag antenna, subject to a small and compact antenna's design configuration have been studied. The present work has been addressed directly to reduce the cost, size and increase the detection range and communication reliability of the RFID framework antennas. Furthermore, the modelling concept of RFID passive tags mounted on various materials including the novel design of RFID reader antenna using Genetic Algorithm (GA) are considered and discussed to maintain reliable and efficient antenna radiation performances. The main benefit of applying GA is to provide fast, accurate and reliable solutions of antenna's structure. Therefore, the GA has been successfully employed to design examples: meander-line, two linear cross elements and compact Helical- Spiral antennas. In addition, a hybrid method to model the human body interaction with RFID tag antenna operating at 900MHz has been studied. The near field distribution and the radiation pattern together with the statistical distribution of the radiation efficiency and the absorbed power in terms of cumulative distribution functions for different orientation and location of RFID's tag antenna on the human body have been demonstrated. Several tag antennas wi th symmetrical and unsymmetrical structure configurations operating in the European UHF band 850-950 MHz have been fabricated and tested. . The measured and simulated results have been found to be in a good agreement with reasonable impedance matching to the typical input impedance of an RFID integrated circuit chip and nominal power gain and radiation patterns.

The efficiency of the conventional, explicit finite difference time domain (FDTD)method is constrained by the upper limit on the temporal discretization, imposed by the Courant–Friedrich–Lewy (CFL) stability condition. Therefore, there is a growing interest in overcoming this limitation by employing unconditionally stable FDTD methods for which time-step and space-step can be independently chosen. Unconditionally stable Crank Nicolson method has not been widely used in time domain electromagnetics despite its high accuracy and low anisotropy. There has been no work on the Crank Nicolson FDTD (CN–FDTD) method for frequency dependent medium. In this thesis a new three-dimensional frequency dependent CN–FDTD (FD–CN–FDTD) method is proposed. Frequency dependency of single–pole Debye materials is incorporated into the CN–FDTD method by means of an auxiliary differential formulation. In order to provide a convenient and straightforward algorithm, Mur’s first-order absorbing boundary conditions are used in the FD–CN–FDTD method. Numerical tests validate and confirm that the FD–CN–FDTD method is unconditionally stable beyond the CFL limit. The proposed method yields a sparse system of linear equations which can be solved by direct or iterative methods, but numerical experiments demonstrate that for large problems of practical importance iterative solvers are to be used. The FD–CN–FDTD sparse matrix is diagonally dominant when the time-stepis near the CFL limit but the diagonal dominance of the matrix deteriorates with the increase of the time-step, making the solution time longer. Selection of the matrix solver to handle the FD–CN–FDTD sparse system is crucial to fully harness the advantages of using larger time-step, because the computational costs associated with the solver must be kept as low as possible. Two best–known iterative solvers, Bi-Conjugate Gradient Stabilised (BiCGStab) and Generalised Minimal Residual (GMRES), are extensively studied in terms of the number of iteration requirements for convergence, CPU time and memory requirements. BiCGStab outperforms GMRES in every aspect. Many of these findings do not match with the existing literature on frequency–independent CN–FDTD method and the possible reasons for this are pointed out. The proposed method is coded in Fortran and major implementation techniques of the serial code as well as its parallel implementation in Open Multi-Processing (OpenMP) are presented. As an application, a simulation model of the human body is developed in the FD–CN–FDTD method and numerical simulation of the electromagnetic wave propagation inside the human head is shown. Finally, this thesis presents a new method modifying the frequency dependent alternating direction implicit FDTD (FD–ADI–FDTD) method. Although the ADI–FDTD method provides a computationally affordable approximation of the CN–FDTD method, it exhibits a loss of accuracy with respect to the CN-FDTD method which may become severe for some practical applications. The modified FD–ADI–FDTD method can improve the accuracy of the normal FD–ADI–FDTD method without significantly increasing the computational costs.

yes / There is an increasing need for accurate models describing the electrical behaviour of individual biological cells exposed to electromagnetic fields. In this area of solving linear problem, the most frequently used technique for computing the EM field is the Finite-Difference Time-Domain (FDTD) method. When modelling objects that are small compared with the wavelength, for example biological cells at radio frequencies, the standard Finite-Difference Time-Domain (FDTD) method requires extremely small time-step sizes, which may lead to excessive computation times. The problem can be overcome by implementing a quasi-static approximate version of FDTD, based on transferring the working frequency to a higher frequency and scaling back to the frequency of interest after the field has been computed. An approach to modeling and analysis of biological cells, incorporating the Hodgkin and Huxley membrane model, is presented here. Since the external medium of the biological cell is lossy material, a modified Berenger absorbing boundary condition is used to truncate the computation grid. Linear assemblages of cells are investigated and then Floquet periodic boundary conditions are imposed to imitate the effect of periodic replication of the assemblages. Thus, the analysis of a large structure of cells is made more computationally efficient than the modeling of the entire structure. The total fields of the simulated structures are shown to give reasonable and stable results at 900MHz, 1800MHz and 2450MHz. This method will facilitate deeper investigation of the phenomena in the interaction between EM fields and biological systems. Moreover, the nonlinear response of biological cell exposed to a 0.9GHz signal was discussed on observing the second harmonic at 1.8GHz. In this, an electrical circuit model has been proposed to calibrate the performance of nonlinear RF energy conversion inside a high quality factor resonant cavity with known nonlinear device. Meanwhile, the first and second harmonic responses of the cavity due to the loading of the cavity with the lossy material will also be demonstrated. The results from proposed mathematical model, give good indication of the input power required to detect the weakly effects of the second harmonic signal prior to perform the measurement. Hence, this proposed mathematical model will assist to determine how sensitivity of the second harmonic signal can be detected by placing the required specific input power.

The aim of this study is to analysis, investigate and find out the solutions for the problems associated with the implementations of antennas RFID Reader and Tag for various applications. In particular, the efficiency of the RFID reader antenna and the detection range of the RFID tag antenna, subject to a small and compact antenna¿s design configuration have been studied. The present work has been addressed directly to reduce the cost, size and increase the detection range and communication reliability of the RFID framework antennas. Furthermore, the modelling concept of RFID passive tags mounted on various materials including the novel design of RFID reader antenna using Genetic Algorithm (GA) are considered and discussed to maintain reliable and efficient antenna radiation performances. The main benefit of applying GA is to provide fast, accurate and reliable solutions of antenna¿s structure. Therefore, the GA has been successfully employed to design examples: meander-line, two linear cross elements and compact Helical- Spiral antennas. In addition, a hybrid method to model the human body interaction with RFID tag antenna operating at 900MHz has been studied. The near field distribution and the radiation pattern together with the statistical distribution of the radiation efficiency and the absorbed power in terms of cumulative distribution functions for different orientation and location of RFID¿s tag antenna on the human body have been demonstrated. Several tag antennas wi th symmetrical and unsymmetrical structure configurations operating in the European UHF band 850-950 MHz have been fabricated and tested. . The measured and simulated results have been found to be in a good agreement with reasonable impedance matching to the typical input impedance of an RFID integrated circuit chip and nominal power gain and radiation patterns.

Dealing with the electromagnetic issue might bring a sort of discontinuous and nondifferentiable regions. Thus, it is of great interest to implement an appropriate optimisation approach, which can preserve the computational resources and come up with a global optimum. While not being trapped in local optima, as well as the feasibility to overcome some other matters such as nonlinear and phenomena of discontinuous with a large number of variables. Problems such as lengthy computation time, constraints put forward for antenna requirements and demand for large computer memory, are very common in the analysis due to the increased interests in tackling high-scale, more complex and higher-dimensional problems. On the other side, demands for even more accurate results always expand constantly. In the context of this statement, it is very important to find out how the recently developed optimization roles can contribute to the solution of the aforementioned problems. Thereafter, the key goals of this work are to model, study and design low profile antennas for wireless and mobile communications applications using optimization process over a computational electromagnetics numerical solution. The numerical solution method could be performed over one or hybrid methods subjective to the design antenna requirements and its environment. Firstly, the thesis presents the design and modelling concept of small uni-planer Ultra- Wideband antenna. The fitness functions and the geometrical antenna elements required for such design are considered. Two antennas are designed, implemented and measured. The computed and measured outcomes are found in reasonable agreement. Secondly, the work is also addressed on how the resonance modes of microstrip patches could be performed using the method of Moments. Results have been shown on how the modes could be adjusted using MoM. Finally, the design implications of balanced structure for mobile handsets covering LTE standards 698-748 MHz and 2500-2690 MHz are explored through using firefly algorithm method. The optimised balanced antenna exhibits reasonable matching performance including near-omnidirectional radiations over the dual desirable operating bands with reduced EMF, which leads to a great immunity improvement towards the hand-held. / General Secretariat of Education and Scientific Research Libya

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)

In this thesis, we have designed and optimized strip waveguide based micro-ring and micro-ring and micro-racetrack resonators for biosensing applications. Silicon-On-Insulator (SOI) platform which offers several advantages over other materials such as Lithium Niobate, Silica on Silicon and Silicon nitride is considered here. High index contrast enables us to miniaturize the biosensor devices and monolithic integration of source and detectors on the same chip. We have considered the dispersive nature of the waveguide and proceeded towards optimization. Finite difference schemes and Finite Difference Time Domain (FDTD) methods are the primary tools used to model the biosensor. Various structures such as channel waveguides and beam structures are analyzed on the basis of their suitability for sensing applications. Strip and Rib waveguides are the two geometries considered in our studies. In an optical guiding structure, effective index of the propagating optical mode can be induced by two different phenomena: i. Homogeneous Sensing In this category, effective index of a propagating optical mode changes with uniformly distributed analytes extending over a distance well exceeding the evanescent field penetration depth. The sample serves as the waveguide cover. ii. Surface Sensing In the case of surface sensing, analytes bound to the surface of the waveguide. The effective index of an optical mode changes with the refractive index as well as the thickness of an adlayer. A thin layer of adsorbed or bound molecules transported from liquid or gaseous medium serving as waveguide cover is referred as an adlayer. Both homogeneous and surface sensing schemes are addresses in this work. By bulk sensing method, the characteristics of bioclad covering the device are studied. Optimization of the resonator structure involves the analysis of following parameters: • Gap between the ring and bus waveguides • Free spectral range • Extinction ratio • Quality factor We have achieved a maximum bulk sensitivity of 115 nm / RIU with ring waveguide width of 450 nm and bus width of 350 nm which is better than an earlier reported value of 70 nm/ RIU. We have proposed a novel detection scheme consisting of a micro-racetrack resonator formed over a cantilever structure. The devoice works on the principle of opto-mechanical coupling to detect conformational changes due to biomolecular adherence. BSA (Bovine Serum Albumin) and IgG ( Immuno Globulin G) are the two proteins considered in the work. Mechanical analysis of the beam for tensile and compressive stresses and corresponding spectral responses of the racetrack resonators are analyzed both by semi-analytical and method and numerical analyzes. We compared various aspects of rib and strip waveguide racetrack resonators. We have proved by numerical simulation, that the device is capable of distinguishing tensile and compressive stress. Two strip waveguides of dimensions : 450 nm X 220 nm and 400 nm X 180 nm, former supporting both Quasi-TE and Quasi-TM modes where as the second configuration allows only Quasi-TE mode alone. Sensitivity of the cantilever sensor is : 0.3196 x 10-3 nm/ µɛ at 1550 nm wavelength.

The emergence of Ultra-wideband (UWB) technology application has yielded tremendous and vital impacts in the field of microwave wireless communications. These applications include military radar imaging, security screening, and tumour detection, especially for early detection of breast cancer. These indicators have stimulated and inspired many researchers to make the best use of this promising technology. UWB technology challenges such as antenna design, the problem of imaging reconstruction techniques, challenges of severe signal attenuation and dispersion in high loss material. Others are lengthy computational time demand and large computer memory requirements are prevalent constraints that need to be tackled especially in a large scale and complex computational electromagnetic analysis. In this regard, it is necessary to find out recently developed optimisation techniques that can provide solutions to these problems. In this thesis, designing, optimisation, development, measurement, and analysis of UWB antennas for near-field microwave imaging applications are considered. This technology emulates the same concept of surface penetrating radar operating in various forms of the UWB spectrum. The initial design of UWB monopole antennas, including T-slots, rectangular slots, and hexagonal slots on a circular radiating patch, was explicitly implemented for medical imaging applications to cover the UWB frequency ranging from 3.1 GHz to 10.6 GHz. Based on this concept, a new bow-tie and Vivaldi UWB antennas were designed for a through-the-wall imaging application. The new antennas were designed to cover a spectrum on a lower frequency ranging from 1 GHz - 4 GHz to ease the high wall losses that will be encountered when using a higher frequency range and to guarantee deeper penetration of the electromagnetic wave. Finally, both simulated and calculated results of the designed, optimised antennas indicate excellent agreement with improved performance in terms of return loss, gain, radiation pattern, and fidelity over the entire UWB frequency. These breakthroughs provided reduced computational time and computer memory requirement for useful, efficient, reliable, and compact sensors for imaging applications, including security and breast cancer detection, thereby saving more lives. / Tertiary Education Trust Fund (TET Fund) Supported by the Nigerian Defence Academy (NDA)