A novel design of a temple shaped printed slot antenna for circular polarization applications is presented in this paper. The slot, half trapezoidal and half semi-circular in shape, is excited by a 50 Ω CPW feed terminated with a tuning stub. Modifications of the initial design for improving return loss and circular polarization characteristics are proposed and discussed. The antenna is very compact (40 mm x 35 mm) in size and simple to design. The final version of the antenna offers an experimentally measured impedance bandwidth of 108% i.e., from 2.75 GHz to 9.25 GHz. The 3-dB axial ratio bandwidth achieved is 51.6% i.e., from 4.6 GHz to 7.8 GHz. The antenna is further characterized by a peak gain of about 5 dB and a relatively stable radiation pattern in the useful band.
This paper presents a Monte-Carlo multidomainpseudospectral time-domain (MPSTD) algorithmdeveloped for the analysis of scattering from a three dimensional (3D)objectburied below arandom rough surface separating two half spaces. In the development, special attention is paid to the 3Dcomputation domain decomposition and subdomain mapping involving the random rough surfaceas well as the subdomain patching along the rough surface. The Mote-Carlo MPSTD algorithm is then employed to determine the scattering of 3D objects of various shapes and electromagnetic properties; embedded in the lower half space with different permittivity and the roughness of the random rough surface may vary.Sample numerical results are presented, validated, and analyzed.Through the analysis, it is observed that the roughness of the random rough surface and the electromagnetic properties of the lower half space can significantly affect the scattered signature of the buried object.
Propagation of Radio Frequency (RF) waves in indoor corridors is very complex and diverse as the propagation effects in the indoor scenarios are those that change over fractions of wavelength. Therefore, understanding of RF propagation characteristics is vital for the design of air interface and estimation of propagation losses is very much needed especially for wireless networks such as randomly deplorable Wireless Sensor Communications. In this research work, short-range, near floor/ground RF propagation path loss measurements at low antenna heights of 2 cm and 50 cm from the floor were made in typical narrow and wide straight indoor corridors at 915/2400 MHz in a modern multi-storied building utilizing RF equipment. Comparisons between measured and simulated path loss values were made utilizing Matlab simulations of Ray-tracing technique, free space and ITU-R models. Mean path loss exponent values were deduced from the measured data. The research work reported in this paper is predominately geared towards characterizing radio link for Wireless Sensor Communications/Networks in typical indoor corridor environments.
Four ultra-wideband (UWB) antennas are proposed: one referenced antenna without notch and three novel antennas with one, two and three notched-bands, respectively. The UWB referenced antenna consists of a beveled rectangular metal patch, a 50 Ω microstrip line and a defective ground plane. Then, by utilizing one, two and three electromagnetic bandgap (EBG) structures on the UWB antenna, respectively, the antennas present one, two and three notched-band responses. The frequency domain characteristics including VSWR, transfer coefficient S21, radiation patterns and Group delay are investigated. It is found that the EBG design approach is a good candidate for frequency rejection at the desired frequencies, owing to high performance of notch design and the notched-band bandwidth controlling abilities. Meanwhile, these abilities also enable less useful frequencies false rejected. The design examples exhibit good band-rejected characteristics in the WiMAX/WLAN interference bands (3.4, 5.2 and 5.8-GHz bands). Moreover, good time-domain characteristics of the antennas are checked based on group delay, waveform response, correlation factor and pulse width stretch ratio (SR). Therefore, the antennas are good candidates for portable UWB devices.
We propose in this paper the design, realization and experimental characterization of a low-profile metamaterial ``bent'' monopole antenna with a total height of 0.027 λ0 and a fractional bandwidth of 24.4% around 1.3 GHz. The metamaterial structure is a dual-layer mushroom-like electromagnetic band gap (DL-EBG) conceived and optimized to improve the antenna's operating bandwidth. Moreover, a ``Sabre-Type'' antenna composed by two identical ``bent'' monopole metamaterial antennas placed on both sides of a composite thin slab material has been simulated and realized. The ``sabre" antenna provides a vertically polarization and omnidirectional radiation patterns in the elevation plane while its radiation patterns are almost directional in the azimuth plane. A maximum gain of 8.7 dB is obtained by measurement at 1.45 GHz. A remarkable agreement is obtained between the measured and the simulated results.
This paper presents an efficient imaging algorithm for Terrain Observation by Progressive Scans (TOPS) mode SAR raw data focusing. First, the use of sub-aperture is adopted to overcome the aliased Doppler spectra due to progress azimuth beam scanning. Afterwards, range compression and range cell migration correction (RCMC) are individually implemented in each azimuth block with its individual Doppler centroid. After azimuth sub-aperture signal recombination, a new Doppler centroid varying rate is introduced to avoid the reconstructed Doppler spectra wrapping. Moreover, azimuth varying beam center time is removed by azimuth frequency scaling before the final azimuth spectrum analysis (SPECAN) step. Finally, the conventional Fourier transform (FT) is replaced by the scaled Fourier transform (SCFT) step to obtain the uniform azimuth space sampling interval. Since the proposed imaging algorithm is without any interpolations and azimuth data extension, it is highly efficient. Simulation results on point targets validate the proposed algorithm.
In this article, an optimized E-shaped patch antenna for Bluetooth (2.4-2.484 GHz) and UWB (3.1-10.6 GHz) applications with WLAN (5.15-5.825 GHz) band-notched characteristics is proposed. The dimensions of the E-shaped antenna structure in addition to the position of the slotted C-shape in the ground plane are optimized using recent optimization techniques such as Modified Particle Swarm Optimization (MPSO), Bacterial Swarm Optimization (BSO), and Central Force Optimization (CFO). The optimization algorithms were implemented using MATLAB-software and linked to the CST Microwave Studio to simulate the antenna. Next, the effects of the Laptop structure on the antenna radiation characteristics are considered. Finally, the antenna structures are simulated by the finite difference time domain method (FDTD) to validate the results. The measured results exhibit good agreement with the simulation from CST and the Finite Difference Time Domain (FDTD) program written with matlab.
We consider three different definitions of magnetic dipole moment for electrically neutral compact bunches of charged particles and show that, in general, they are not equivalent to each other with respect to their relativistic transformation. In particular, we prove that the "configurational" definition of magnetic dipole moment mc = 1/2∫v(r × j)dV (in the common designations) and its definition through generated electromagnetic field ("source" definition ms) or experienced force ("force" definition mf) lead to different relativistic transformations of mc and ms (mf). The results obtained shed light on the available disagreements with respect to relativistic transformation of a magnetic dipole moment, and they can be used in covariant formulation of classical electrodynamics in material media.
The aim of this paper is to propose and evaluate a semi-empirical propagation modeling for radiating cable used in indoor environments. This propagation modeling takes into consideration propagation mechanisms such as reflections, penetration loss and cable termination that result from a particular environment, as well as specific cable paths that actual propagation models for radiating cable systems have not considered. The proposed modeling is carried out using three different propagation models and has been experimentally validated by sets of measurements performed in a university building in the frequency range from 900 MHz to 2.5 GHz. A careful selection of the data sets validates the robustness of the proposed model. The results show a mean of the error less than 1 dB while the standard deviation is between 2.2 dB and 4.6 dB in all cases. To the best of our knowledge, this is the first time such a robust modeling for radiating cable operating between 900 MHz to 2.5 GHz has been presented.
The problem of characterizing random sources from near-field measurements and of devising the random field sampling procedure is tackled by a stochastic approach. The presented technique is an extension of that introduced in [A. Capozzoli, et al., Field sampling and field reconstruction: a new perspective, Radio Sci., vol. 45, 2010] and successfully adopted to experimentally characterize deterministic (CW and multi-frequency) radiators and fields. Under the assumption that the source is wide sense stationary, quasi-monochromatic and incoherent, its intensity is reconstructed by time-domain field measurements aimed at extracting information from the mutual coherence of the acquired near-field. The linear relation between the field coherence and the source intensity is inverted by using the Singular Value Decomposition (SVD) approach, properly representing the source intensity distribution by exploiting the a priori information (e.g., its size and shape) on the radiator. The sampling of the radiated random field is devised by a singular value optimization procedure of the relevant finite dimensional linear operator. Experimental results using a slotted reverberation chamber as incoherent source assess the performance of the approach.
We theoretically investigate the possibility of using a metamaterial structure as a spacer, named as metaspacer, which can be integrated with other materials in microfabrication. We show that such metaspacers can provide new optical behaviors that are not possible through conventional spacers. In particular, we investigate negative index metaspacers embedded in fishnet metamaterial structures and compare them with conventional fishnet metamaterial structures. We show that the negative index metaspacer based fishnet structure exhibits intriguing inverted optical response. We also observe that the dependence of the resonance frequency on the geometric parameters is reversed. We conclude with practicality of these metaspacers.
The analysis of scattering of objects buried below a random rough surface is of practical interest. In reality, the random rough surface may be of an extensive periodic structure. To deal with this more realistic situation, this paper presents a Monte-Carlo MPSTD numerical technique developed for investigating the scattering of a cylinder buried below a random periodic rough surface. The computation model is formulated in two steps. In the first step, only the random rough surface is considered and the periodic boundary condition (PBC) is enforced at the two ends of a period of the rough surface. Then, in the second step, a cylinder is placed below the random rough surface and the interaction between the buried cylinder and the rough surface is taken into account. In each of the two steps, the fields are computed employing the MPSTD algorithm developed in the authors' previous work. Sample numerical results are presented and validated.
This paper deals with the prediction of magnetic field distribution and electromagnetic performances of parallel double excitation and spoke-type permanent magnet (PM) motors using simplified (SM) and exact (EM) analytical models. The simplified analytical model corresponds to a simplified geometry of the studied machines where the rotor and stator tooth-tips and the shape of polar pieces are not taken into account. A 2D analytical solution of magnetic field distribution is established. It involves solution of Laplace's and Poisson's equations in stator and rotor slots, airgap, buried permanent magnets into rotor slots and non magnetic region under magnets. A comparison between the results issued from the simplified model with those from exact model (EM) (which represents a more realistic geometry with stator and rotor tooth-tips and the shape of polar pieces) is done to show the accuracy of the simplified geometry on magnetic field distribution and electromagnetic performances (cogging torque, electromagnetic torque, flux linkage, back-EMF, self and mutual inductances). The analytical results are verified with those issued from finite element method (FEM).
In this work we investigate the effect of broadband antireflection of a medium by a layer of embedded nano-cavities arranged near the surface. It is shown that this structure is versatile and allows near 100% transmittance in a wide spectral range practically for any dielectric material. The approximate model of nano-structured layer is suggested that allows to determine the parameters of the system necessary for achieving antireflection of any a priori given media without complicated numerical calculations. The transmission spectrum of a medium modified by such a structure is entirely defined by a radius and a depth of bedding of the nano-porous layer.
A simple and effective double-thresholding strategy based on energy estimation is proposed to choose the optimal boundary between the signal subspace and noise subspace in TR-MUSIC algorithm for microwave imaging of extended targets. Simulations and imaging results are given to demonstrate its strong noise rejection and super-resolution capability. In the new method, the shape details of extended targets can be obtained from single frequency or multi-frequency scattering data.
With an increase in the number of high speed applications, researchers have been concentrating on permanent magnet bearings due to their suitability. This paper presents a mathematical model of a permanent magnet bearing made of ring magnets with radial polarizations. Coulombian model and vector approach are used to estimate the force, moment and stiffness. A MATLAB code is developed for evaluating the envisaged parameters for three degrees (translational) of freedom of the rotor. The proposed model is validated with the available literature. Comparison of force and stiffness results of the presented model with that reported in the literature and also with the results of 3D finite element analysis shows good agreement. Then, it is extended to analyse stacked ring magnets with alternate radial polarizations. Finally, the cross coupled stiffness values in addition to the principal stiffness values are presented for the elementary structure and also for stacked structure with three ring permanent magnets with alternate radial polarizations.
Fresnel coefficients for three-layered uniaxially anisotropic media with arbitrarily oriented optic axes have been obtained using half-space reflection and transmission coefficients. The optic axes of the anisotropic media are assumed to be tilted at different angles ((Ψi, χi), i = 1,2). This gives arbitrary orientation for anisotropic medium in the stratified configuration. The half space coefficients are derived at the boundary surfaces of two different media including isotropic-anisotropic, anisotropic-anisotropic, anisotropic-isotropic interfaces with the application of boundary conditions. The interface between two media for the three-layered media leads to four different cases of wave propagation, which are analyzed in detail. The results are compared with the existing results in the limiting cases analytically. The results presented in this paper can be used to establish dyadic Green's functions, which can be used to calculate radiation and scattering from the stratified structure.
The launching of high-frequency electromagnetic waves into fusion plasmas is an effective method for plasma heating and noninductive current drive. In addition, the reflection of electromagnetic waves on the plasma cutoffs is utilized in electron density diagnostic measurements. The scope of this article is to comment on the standard approximations made in the simulation of electron-cyclotron wave propagation and absorption in tokamak plasmas, in connection to the established modeling tools and the underlying physics, as well as to illustrate the limits of their validity, especially regarding the applicability to ITER-related studies and beyond. The identification of possible gaps in the current state-of-the-art and the implication of new requirements for theory and modeling are also discussed.
Current shielding effectiveness (SE) of electromagnetic shielding (EMS) fabric is tested in the plane state, the testing results are difficult to describe the shielding effect of a garment in a curve surface state after manufactured by the fabric. To solve this problem, this study proposes a new SE computation model of the EMS fabric based on a SE vector. The model can calculate a theoretical SE value of the EMS fabric in the curve surface state. A number of factors which determine the SE of the fabric with a curve surface are analyzed according to the principle of the reflection and transmission of the electromagnetic wave. This study also gives a new argument that the curve fabric can be divided into many micro-planes and the fabric SE is considered as a vector. And then a computation model of the SE of the curve fabric is constructed. The detail of computation is deduced, and an application example is given. Results of experiments and analyses show that the method is scientific and correct, and the error between the computation SE value and the testing SE value of the local garment is less than 3%. The model provides a new way to calculate the SE of the EMS fabric with symmetric curved surface.
A novel implementation of aggressive space mapping (ASM) for the automatic layout synthesis of planar metamaterial structures is outlined in this article. Specifically, we employ a model-trust region optimisation approach to significantly reduce the computational burden associated with the direct optimisation of high-fidelity models. A Visual Basic for application (VBA) link to a commercial full-wave electromagnetic (EM) solver is created, to ensure that the automated Matlab-based platform has complete control of the design and analysis of the entire ASM process. The validity and efficiency of our approach is demonstrated with examples of complementary split-ring resonator (CSRR)-loaded transmission lines, comparing both modified and unmodified version of the quasi-Newton iteration within the ASM framework.