The design of concentric ring arrays for isoflux radiation is presented in this paper. This design considers the reduction of the side lobe level and isoflux radiation requirements for Medium Earth Orbit (MEO) satellites. The optimization problem considers the spacing among rings and levels of amplitude excitations. The well-known method of Particle Swarm Optimization (PSO) is utilized for this design case. The obtained results could cause the satellite hardware to be reduced significantly even more than that presented previously in the literature.
Ultrawideband (UWB) microwave imaging is a promising emerging method for the detection of breast cancer. Fibroglandular tissue has been shown to significantly limit the effectiveness of UWB imaging algorithms, particularly in the case of premenopausal women who may present with more dense breast tissue. Rather than trying to create an image of the breast, this study proposes to compare the UWB backscattered signals from successive scans of a dielectrically heterogeneous breast, to identify the presence of cancerous tissue. The temporal changes between signals are processed using Support Vector Machines to determine if a cancerous growth has occurred during the time between scans. Detection rates are compared to the results from a previous study by the authors, where UWB backscatter signals from a single scan were processed for cancer detection.
The microwave transmission of hexagonal arrays consisting of patches of equilateral aluminium triangles has been experimentally studied as a function of metal occupancy (triangle size). As one would expect, at low frequencies the microwave transmission drops on passing through the connectivity threshold (50%) when the disconnected hexagonal array of metal triangles switches to a disconnected hexagonal array of equilateral holes. However, for higher frequencies resonant phenomena cause a complete reversal in this behaviour such that the transmission, on passing through the connectivity threshold, increases substantially.
The diffraction field asymptotics on the edges of a slot in the plane conducting screen and of a complementary strip is considered using the exact solutions of corresponding stationary diffraction problems, which have been derived before on the bases of the slot (strip) field expansions into discrete Fourier series. It is shown that as nearing the slot (strip) edges, the fields decrease or increase indefinitely in magnitude by the power law with an exponent of modulus less than unity, so the given exact diffraction solutions yield finite value of electromagnetic energy density in any point of space.
This paper presents the electromagnetic field expressions for 3D cassegrain system embedded in a bi-isotropic chiral medium. Mathematical formulation of Maslov is used to find the field expressions in the focal region. Effect of chirality (both the week and strong) on focal region fields is analyzed. It is seen that when the chirality effect is weak (i.e., κ < 1), chiral medium will support positive phase velocity (PPV) for both the left circularly polarized (LCP) and the right circularly polarized (RCP) modes. However for strong chiral medium (i.e., κ > 1), one mode travels with PPV and the other mode travels with negative phase velocity (NPV). The line plots are given to show the behavior of fields in the focal plane of 3D cassegrain system by changing the chirality parameter (κ).
This paper investigates the near field focusing behavior corresponding to the hyperbolic dispersion regime at the second band of the square lattice photonic crystal (PC). Numerical studies reveal the influence of the corner part negative refraction in the observed focusing effect, though the major part of the refraction is divergent at this hyperbolic regime. It is further observed that the investigated dispersion shows the surface mode behavior when the effective index of the PC slab is higher than the air medium. This aspect may be implemented for the excitation and transfer of near fields for an evanescent wave microscopy.
This paper presents an innovative design approach that improves the characteristics of rectangular dielectric resonator antenna (RDRA). In this design the dielectric resonator (DR) fed by microstrip line feed through a rectangular ring slot. This slot represents the coupling mechanism between the resonator and microstrip line. Both DR and slot are resonant structures. Further a comparative study is made by depicting a metallic patch over the DR. The antenna has been fabricated and measured for the study, such as impedance bandwidth, return loss, radiation pattern and antenna gain. Measurement results show dual band property with an achievable impedance bandwidth of 63.67% with return loss of -34.3 dB and antenna gain 2.32 dB.
We investigate the properties of nonlinear envelope pulses developed in a coupled composite right- and left-handed (CRLH) transmission line with regularly spaced Schottky varactors. It is found that the dispersive distortion of the envelope pulses carried by each mode is well compensated by nonlinearity introduced by the varactors. In addition, we numerically observe that the collision of two nonlinear envelope pulses leads to the development of a new pair of envelope pulses (one traveling forward and the other backward). The newly developed pulses become maximal when phase-matching with the original pulses is established, and their carrier frequency is close to that of the harmonics of the colliding pulses.
A regular cross terms algorithm is derived for the parameter estimation of the multi-component polynomial phase signals in additive white Gaussian noise. The basic idea is first to separate its phase parameters into two sets by nonlinear procedures£¬and then each set has half of the parameters in its auto-terms. Furthermore, using two linear transforms to deal with the two signals respectively, the phase coefficients of cross terms can be regulated for the identification and elimination of false peaks caused by the cross terms. Simulations are presented to illustrate the performance of the proposed algorithm.
This work deals with the inverse source problem starting from the knowledge of the radiated field in the near field zone. The inverse problem is stated as the inversion of a linear integral equation and the Singular Value Decomposition (SVD) is exploited as an analysis and inversion tool. In particular, here, we deal with a 2D geometry and aim at comparing the features of the inverse problem in dependence on the nature of the source (electric or magnetic).
We present the GPUs computation acceleration for a very recurrent electromagnetic problem which is the calculation of the field radiated by electric dipoles in a multilayer structure (Green's tensor in stratified background), based on the well-known Sommerfeld integrals. Using an optimized parallelization scheme, huge computation acceleration is obtained. Applications of such a work are very broad, especially for the modeling of stratified light emitting devices, or as a building block for the calculation of optical scattering by complex shape structures, when using methods as discrete dipole approximation (DDA) or method of moments (MoM) for example.
This paper presents the results of Boundary Element Method (BEM) numerical procedures of voltages distribution between transmission lines in order to investigate the theoretical corona discharges. The algorithm of the voltage distributions are coded in Mathematica studying size of the system under controlling Neumann and Dirichlet boundary conditions. Conducting experimental work at a high voltage (HV) is potentially very dangerous. Therefore, simulation is a vital research approach, and computer modeling offers significant advantages to estimate optimal calculation over established system to prevent dangerous voltage and not to exceed the corona voltage. In this paper, the BEM results are verified with Finite Element Methods (FEM) which is coded in Mathematica too.
In this paper, the performance of conventional Uniplanar Compact Photonic Band Gap (UC-PBG) structures is investigated under different bending extents. The structure under study is operated as an Artificial Magnetic Conductor (AMC) in which performance is mainly characterized by its resonant frequency and bandwidth. Modelling and numerical analysis have been carried out using CST Microwave Studio simulation software which is based on Finite Integration Technique (FIT). Results show that different bending extents affect the AMC's performance which is specified by a shift to higher resonant frequencies and bandwidth degradation when the degree of bending is increased. Furthermore, we point out some important simulation tips to avoid inaccurate and/or invalid results. This type of study is important to evaluate the performance of such structures for conformal applications. To the best of the authors' knowledge, such type of systematic study is being reported for the first time.
In this paper, we use the Bloch theorem and transfer matrix method to calculate the dispersion relation of a ternary 1D photonic crystal with left-handed materials. Then, we obtain the total omnidirectional reflection band gaps of this structure. We demonstrate that the omnidirectional reflected frequency bands are enlarged in comparison with ordinary materials with positive index of refraction.
We propose a metamaterial coplanar stop-band filter made of multi-turn rectangular spiral particles. Numerical and experimental results show the feasibility of devices with dimensions more than 10 times smaller than those in the literature and with good performances.
Magnetic refrigeration is an innovative, revolutionary, efficient and environmentally friendly cooling technology which is on the threshold of commercialization. The essential components of magnetic refrigeration system are the magnetic field generator and the magnetocaloric material. The two main goals of this paper are to design and to optimize a permanent magnet magnetic refrigeration machine for power cooling generation, where an initial configuration is studied and based on this study two other configurations are presented. Both electromagnetic and thermal studies are explored. The electromagnetic design part has been accomplished by using the finite elements method and the thermal design part has been achieved using the finite difference method. 57
This paper is a theoretical investigation and analysis of the focal region fields of a hyperbolic focusing lens embedded in chiral medium. Chiral-dielectric and dielectric-chiral interfaces are studied and the behavior of waves after passing through these interfaces are discussed. Geometric optics (GO) is used initially. However, it fails around the focal region because it gives non-realistic singularity in this region. So, Maslov's method is used in the caustic region and the field analysis is made. The effect of chirality variation on the amplitude of the fields around the focal region is given and discussed.
A new radar cross section (RCS) prediction technique based on beam tracing is presented. The incident plane wave is modeled as a set of trigonal ray tubes, and each ray tube is traced and recursively subdivided as its reflection aspect. The calculation time of the proposed method is independent of target size. The proposed method provides accurate solutions and is efficient for RCS analysis of electrically large targets.
DeDesign procedure for a modified Composite Right/Left Handed (CRLH) unit cell is represented. The ferroelectric interdigital capacitor (IDC) is used as a tuned capacitor, and spiral inductor is utilized to implement inductors. A modified CRLH unit cell is attained by moving the shunt inductor of conventional unit cell to both ends with doubled values. In this manner, only one bias network would be required for each unit cell. The parameters of the designed unit cell are obtained so that the Bloch impedance to be equal to 50Ω and the Bloch propagation constant to have one zero at the operational frequency. The operational frequency is chosen equal to 11.45 GHz, which is in the Ku-band and in middle of the up-link satellite communications. To design the modified unit cell, initially, the unit cell without a shunt capacitor is constructed. This would result in Π-model structure for which the element dimensions are varied to reach the desired values. Next, the shunt capacitor is added to the model and its length is varied until the balanced condition is achieved.
In this paper, transmission properties of stacked split ring resonators metasurfaces in free space and under normal incidence are investigated experimentally and numerically. Emphasis is put on studying the interaction between adjacent SRRs metasurfaces. The thorough analysis of the electromagnetic fields shows that both magnetic and electric coupling can occur between adjacents metasurfaces for vertical and horizontal polarization. In addition, we found that all propagating bands within our spectral window (up to 20 GHz) support right-handed behaviour. Both simulation and experiment results in the microwave regime are in good agreement.
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