We numerically and experimentally evaluate different designs of coplanar waveguides (CPWs) loaded with split ring resonators (SRRs) and complementary split ring resonators (CSRRs), respectively. In particular, we are interested in their stop-band performance. Starting from structures which consist of two concentric rings, we study devices with only an outer ring, an inner ring or multiple concentric rings. Furthermore, our study shows that introducing slots in the proximity of the SRR or CSRR will modify the stop-band considerably. Single and multiple unit cells for both designs are fabricated and measured. Our results demonstrate the potential of the CSRR/CPW structure for filter applications.
This paper presents a comparative analysis between the experimental characterization and the numerical simulation results for a three-dimensional FCC photonic crystal (PhC) based on a self-assembly synthesis of monodispersive latex spheres. Specifically, experimental optical characterization, by means of reflectance measurements under variable angles over the lattice plane family [1,1,1], are compared to theoretical calculations based on the Finite Difference Time Domain (FDTD) method, in order to investigate the correlation between theoretical predictions and experimental data. The goal is to highlight the influence of crystal defects on the achieved performance.
Microwave Imaging (MI) has been widely investigated as a method to detect early stage breast cancer based on the dielectric contrast between normal and cancerous breast tissue at microwave frequencies. Furthermore, classification methods have been developed to differentiate between malignant and benign tumours. To successfully classify tumours using Ultra Wideband (UWB) radar, other features have to be examined other than simply the dielectric contrast between benign and malignant tumours, as contrast alone has been shown to be insuficient. In this context, previous studies have investigated the use of the Radar Target Signature (RTS) of tumours to give valuable information about the size, shape and surface texture. In this study, a novel classification method is examined, using Principal Component Analysis (PCA) to extract the most important tumour features from the RTS. Support Vector Machines (SVM) are then applied to the principal components as a method of classifying these tumours. Finally, several different classification architectures are compared. In this study the performance of classifiers is tested using a database of 352 tumour models, comprising four different sizes and shapes, using the cross validation method.
This paper presents the comparison results between two new generator configurations. These generator units are namely a field assisted switched reluctance generator (SRG) and a brushless dc (BLDC) generator. No permanent magnets are used in either unit. The field assisted SR generator consists of two magnetically dependent stator and rotor sets (layers), where each stator set includes twelve salient poles with windings wrapped around them, while the rotor comprises of eight salient poles without any winding or permanent magnet. There is a stationary reel, which has the field coil wrapped around it and is placed between the two-stator sets. The BLDC generator is also made up of two magnetically dependent stator and rotor sets, but each stator set includes nine salient poles with windings wrapped around them while, the rotor comprises of six salient poles without any windings or permanent magnets. There is also a stationary reel between the two layers to produce the magnetic field through the motor assembly. This magnetic field travels through a guide to the rotor then the stator and finally completes its path via the generator housing. The generator phase windings for each layer are connect such that all the stator poles in that set can have either north or south pole configuration while the stator poles in the other layer have the opposite pole arrangement. This type of connection can be used in motoring mode as well. To evaluate the performance of the generators, two types of analysis, namely, numerical technique and experimental study have been utilized. In the numerical analysis, three dimensional finite element analysis is employed, whereas in the experimental study, proto-types have been built and tested.
The appropriateness of dielectric loaded antenna for the passive millimeter wave imaging application has recently been demonstrated. In this paper, we analyze the optical performance of the passive millimeter wave (PMMW) imaging system based on a 1D focal plane array (FPA) of dielectric rod waveguide (DRW) antennas. A first step in the design process is to analyze the image quality potential of 1D FPA-based imaging system in terms of the point spread function (PSF) and the modulation transfer function (MTF). We consider the effect of lens, DRW antenna, electromagnetic crosstalk between adjacent DRW antenna elements in the array, and sampling. From simulation and measurement, we found that the image quality in the passive millimeter wave imaging system with a DRW antenna array is less sensitive to electromagnetic crosstalk between antenna elements in the array. The measurements and simulations show that the system is diffraction limited and also closely agrees with the Rayleigh criterion of resolution for diffraction limited optical systems.
In this paper, the design and development of a novel active antenna including circuits for Ultra-wide band (UWB) pulse generation and transmission have been described. In this design a pulse with pulse-width approximately 150 ps and amplitude 500 mV (peak-to-peak) was generated using a single high electron mobility transistor (HEMT) as the active device (and an optional Schottky diode for enhanced performance), this being the simplest circuit for generating UWB pulses as far as we know. This circuit was integrated with a newly designed UWB planar microstripfed slot antenna, which is an active antenna in the sense that in addition to radiating the signal, it also acts as a filter, which tailors the spectrum of the transmitted pulse to a shape close to that recommended for UWB communications. We have also given a quantitative analysis, which explains the operation of the circuit.
In the framework of the Green function method, we theoretically study the photonic band structure of one-dimensional superlattice composed of alternating layers of right-handed and left-handed materials (RHM and LHM). The dispersion curves are studied by assuming that the dielectric permittivity and magnetic permeability are frequency dependent in each layer. It is shown that such structures can exhibit new types of electromagnetic modes and dispersion curves that do not exist in usual superlattices composed only of RHM. With an appropriate choice of the parameters, we show that it is possible to realize an absolute (or omnidirectional) band gap for either transverse electric (TE) or transverse magnetic (TM) polarizations of the electromagnetic waves. A combination of two multilayer structures composed of RHM and LHM is proposed to realize, in a certain range of frequency, an omnidirectional reflector of light for both polarizations.
A novel robust adaptive beamforming method for conformal array is proposed. By using interpolation technique, the cylindrical conformal array with directional antenna elements is transformed to a virtual uniform linear array with omni-directional elements. This method can compensate the amplitude and mutual coupling errors as well as desired signal point errors of the conformal array efficiently. It is a universal method and can be applied to other curved conformal arrays. After the transformation, most of the xisting adaptive beamforming algorithms can be applied to conformal array directly. The efficiency of the proposed scheme is assessed through numerical simulations.
Micrometer and sub-micrometer sized non-magnetic particles were manipulated by an external strong magnetic field (e.g. 10 Tesla) with a high gradient. During the strong magnetic field effects, segregation of the non-magnetic particles was observed which could not be realised only with gravitational field. Numerical calculations were subsequently carried out to understand the effects on the insulating particles in a conductive liquid matrix. The migration of micrometer sized particles is obviously enhanced by the magnetic field gradient. Combining the experimental results and theoretical analysis, particle-particle magnetic interaction was found to influence the overall segregation of the particles as well. Magnetised by the strong magnetic field, magnetic interaction between non-magnetic particles becomes dominant and a self-assembly behavior can be demonstrated. Various factors such as the magnetic dipole-dipole interaction and chain-chain interaction, are governing the particles assembly. According to calculations, magnetic field should be strong enough, at least 7 T in order to obtain the assembly morphologies in the present case.
The time domain Maxwell's equations are numerically solved using a multigrid method in a scattered field formulation and a cell-vertex based finite volume time domain framework. The multilevel method is an adaptation of Ni's [9] cell-vertex based multigrid technique, proposed for accelerating steady state convergence of nonlinear Euler equations of gas dynamics. Accelerated convergence to steady state of the time domain Maxwell's equations, for problems involving electromagnetic scattering, is obtained using multiple grids without the use of additional numerical damping usually required in nonlinear problems. The linear nature of the Maxwell's system also allows for a more accurate representation of the fine-grid problem on the coarse grid.
An approach based on acoustics and its theoretical analogies to electromagnetism is used in the present research to study the detection of the acoustic wave energy radiated by the thermal random motion of material particles of the brain during activation or caused by pathology. Pressure and particle velocity are calculated in analytical mathematical forms for the case of human brain monitoring, which can be implemented by a prototype passive acoustic brain monitoring system (PABMOS). Representing theoretically the configuration of this approach, a sphere is used to model the human head and an internal point source in order to simulate potential pressure alterations due to intracranial abnormalities or local functional activations. Finally, numerical results concerning the particle velocity (pressure field distribution) at the surface of the head model, which can implicitly be measured by the suitable piezoelectric sensors of the system, for arbitrary positions of the internal source, are presented.
In this paper, we introduce a different approach of previously reported method to determine absorption and emission cross-sections (δ_{a} and δ_{e}), and dopant concentration in Erbium doped optical fibers (EDOFs) with low background loss (α). We call this new method as variant input single cutback method (VISCM). There is technical similarity between VISCM and conventional cutback method (CCM) for determination of cross-sections, but in former pump and signal powers are not used together. We numerically verify the effect of different parameters such as input power, background loss, and EDOF amplifier cutback length on the cross-sections using VISCM and CCM. We also present the simulation results of maximum gain and optimum length using obtained cross-sections by two methods. We show that the VISCM presents more accuracy than that of CCM in any conditions. In the presence of α, both CCM and VISCM give not actual but pseudo values for the δ_{a} and δ_{e}. Using pseudo parameters values obtained by VISCM for α < 10 dB/km, the error of maximum gain and optimum length of designed EDOF is shown negligible.
This paper presents modeling of the complex permeability spectra, fabrication and a wide frequency range characterization of a toroidal LTCC ferrite sample. A commercial ferrite tape ESL 40012 is used, and standard LTCC (Low Temperature Co-fired Ceramic) processing has been applied to the sample fabrication. The characterization was performed using a short coaxial sample holder and a vector network analyzer in the frequency range from 300 kHz to 1 GHz, at different temperatures. Using the model of the complex permeability spectra dispersion parameters of ferrite LTCC material has been determined for various temperatures. Characteristics of test samples are compared with modeled results and commercially available toroid made of similar NiZn ferrite material.
The diffraction of a uniform unit-amplitude E-polarized plane wave is considered in the case of its normal incidence on a strip periodic metal grating placed on the anisotropic hyrotropic ferromagnetic half-space boundary. The Dirichlet boundary conditions on the grating strips, the medium interface conjugation conditions, the Meixner condition that the energy is finite in any confined volume and the radiation condition are applied, and the boundary value diffraction problem in terms of Maxwell's (Helmholtz) equations is equivalently reduced to the dual system of functional equations with exponential kernel. The system is shown to be the Riemann-Hilbert problem in analytic function theory with the conjugation coefficient differing, in general, from ``-1" and dependent on the incident wave frequency. An analytical regularization procedure based on the Riemann-Hilbert boundary value problem solution with the following use of the Plemelle-Sokhotsky formulas is suggested, resulting in the system of linear algebraic equations of the second kind with a compact operator. For vthese systems, the truncation technique possibility has been shown. Calculation algorithms and simulation packages in terms of C++ language have been developed. As a result, the reflection coefficient performance has been studied over sufficiently wide ranges of frequency and constitutive and geometrical parameters of the electrodynamical systems of interest. The frequency bands of the reflection coefficient resonant behavior have been established and examined. A numerical analytical model of these resonances has been proposed.
Time-modulated antenna arrays attracted the attention of researchers for the synthesis of low/ultra-low side lobes in recent past. This article proposes a Multi-objective Optimization (MO) framework for the design of time-modulated linear antenna arrays with ultra low maximum Side Lobe Level (SLL), maximum Side Band Level (SBL) and main lobe Beam Width between the First Nulls (BWFN). In contrast to the conventional optimization-based methods that attempt to minimize a weighted sum of maximum SLL, SBL, and BWFN we treat these as three different objectives that are to be achieved simultaneously and use one of the best known Multi-Objective Evolutionary Algorithms (MOEAs) of current interest called MOEA/D-DE (Decomposition based MOEA with Differential Evolution operator) to determine the best compromise among these three objectives. Unlike the single-objective approaches, the MO approach provides greater flexibility in the design by yielding a set of equivalent final solutions from which the user can choose one that attains a suitable trade-off margin as per requirements. We compared time-modulated antenna structures with other linear array synthesis such as the excitation method and the phase-position synthesis method on the basis of the approximated Pareto Fronts (PFs) yielded by MOEA/D-DE and the best compromise solutions determined from the Pareto optimal set with a fuzzy membership-function based method. The final results obtained with MOEA/D-DE were also compared with the results achieved by three state-of-the-art single objective optimization algorithms. Our simulation studies on three significant instantiations of the design problem reflect the superiority of the MOEA-based design of time-modulated linear arrays.
A rigorous analytical procedure is developed that allows the exact evaluation of the complete integral representations for the time-harmonic electromagnetic (EM) field components generated by a vertical magnetic dipole (VMD) lying on the surface of a flat and homogeneous lossy half-space. Closed-form expressions for the radial distributions of the EM field components induced on the surface of the half-space are provided in terms of exponential functions and modified Bessel functions. Such expressions make it possible to overcome the limitations implied by the previously published quasi-static solutions, which are valid only in the low-frequency range. Numerical results are presented to show where the quasi-static approximations deviate from the exact solutions for a given homogeneous medium as frequency is changed. The computed amplitude and phase frequency spectra of the EM field components demonstrate that the quasi-static approach fails at frequencies higher than 1 MHz, and that, in particular, it leads to underestimating the EM field strength. Finally, it is also shown that at a frequency equal to or greater than 10 MHz excellent results in terms of accuracy may be obtained by using the high-frequency asymptotic forms of the exact solutions.
A hybrid method is proposed to compute the radar cross section (RCS) of multiple wire scatterers with an arbitrary orientation. Foldy-Lax equations in vector form are transformed into self-consistent equations for including the multiple scattering effects between scatterers. A thin-wire approximation of a method of moment (MoM) is used for calculating the scattering transition operator of a single wire scatterer. To verify the proposed method, two measurement models are fabricated and measured in a compact range chamber. The measured results agree well with the results of the proposed method.
The framework of our work is the application of a fast method to estimate the radiation pattern of an antenna from the measurement of the electric-field magnitude in the near-field region using infrared (IR) camera. IR acquisition techniques allows quasi-realtime measurements of the magnitude of the electrical field on planar surfaces in near-field conditions. However the antennas radiation patterns can only be estimated from near-field electrical magnitude and phase measurements. Consequently a classical plane to plane iterative phase retrieval process has been developed and tested with respect to a large number of configuration parameters such as to find an optimal configuration on a wide frequency range [0.5-20GHz]. In order to achieve and validate such a study, some comparisons have been performed on data obtained either by numerical simulation or classical near-field technique based upon radio-frequency (RF) probe scanning on simple horn antennas. Among all the studied parameters we will focus onto the influence of the dynamic range of the measurements on the reconstructed radiation patterns and on validations from experimental results.
In this study, the transmission of planar single-layer frequency selective surface (FSS) has been studied using modal analysis method, and the maximum transmission that a planar single-layer FSS structure with an infinitely thin array can reach is presented. The results show that this transmission upper limit is independent of the array and the element, which indicates that it is impossible to achieve a transmission higher than this upper limit under a given incident and dielectric-supporting condition by the design of the periodic array. As the modal analysis method is an accurate method to solve the scattering problem of planar FSS with an infinitely thin array, this upper limit is also independent of the solution method. Results of both numerical simulations and experiments show that the upper limit presented in this paper is strict, but may be hard to attain when FSS is supported by lossy dielectric mediums.
Diffraction of scalar plane waves by resistive surfaces are investigated by defining a new boundary condition in terms of the Dirichlet and Neumann conditions. The scattering problems of waves by a resistive half-plane and the interface between resistive and perfectly magnetic conducting half-planes are examined with the developed method. The resulting fields are plotted numerically. The numerical results show that the evaluated field expressions are in harmony with the theory.