In this paper, some design criteria for a Tubular Linear Induction Motor (TLIM) as a fast actuator are considered. The in fluence of geometrical and physical parameters on the operating conditions of a TLIM are investigated by means a quasi-analytic model. The model is based on the application of the Fourier Transform both in space and in time. The Fourier transform in space is introduced to take into account the finite length of the stator windings in the axial direction. The transient electrical response of the motor at standstill following the insertion of a three-phase system of voltage generators is performed by the Fourier transform in the time.
In this paper, we report experimentally and numerically on coupling effects of dielectric metamaterial dimer (metadimer) which composed of two identical ceramic cubes with high permittivity. The distance dependence of Mie resonance for metadimer is investigated under various polarizations of external wave. By changing the configurations and alignment of dimer resonator, it is revealed that magnetic and electric resonances of metadimer exhibits a red/blue shift, resulting from longitudinal or transverse coupling effects of dipoles. Besides, quasi bound states between tightly stacked dielectric cubes are also been pointed out for electric Mie resonance, which is responsible for an unexpected frequency shift with a reverse variation.
ISAR imaging of maritime targets has greater success than other ISAR applications due to the constant oscillatory motions induced by waves and wind. However, relative target motions are usually unknown, difficult focusing, image interpretation and target classification. Using interferometry to obtain the height information makes possible to obtain a 3-D reconstruction of a target, aiding image focusing, image interpretation and target classification. However, the information and utility of the ISAR image and the interferometric information depends highly on geometry and targets dynamics. In this paper we will study the influence of movement dynamics in interferometric ISAR imaging using a realistic extended moving target simulation, a general geometry and complex dynamics models.
The analysis of an antenna mutual coupling is a significant issue for designing the wireless communication system especially includes an array mutual coupling problem. The accurate analysis of the mutual coupling between antennas is needed. Accordingly, several methods for the mutual impedance calculation of dipoles have been studied in cases of coplanar-skew and nonplanar-skew. This paper proposes an exact and simple method for analyzing the mutual impedance between two arbitrarily located and slanted dipoles using the modified induced EMF method; their expressions and the exact analytic solution. The proposed formula and their closed-form solutions are verified by numerical solution using HFSS and give good agreement.
In this paper an explicit finite-difference scheme is developed in staggered grids for solving the Maxwell's equations in time domain. We are aimed to preserve the discrete zero-divergence condition in the electrical and magnetic fields and conserve the inherent laws in non-dispersive simple media all the time using the explicit second-order accurate symplectic partitioned Runge-Kutta temporal scheme for the time derivative terms. The spatial derivative terms in the semi-discretized Faraday's and Ampere's equations are then approximated to get an accurate numerical dispersion relation equation that governs the numerical angular frequency and the wavenumbers for the Maxwell's equations defined in two space dimensions. To achieve the goal of getting the best dispersive characteristics in the chosen grid stencil, a fourth-order accurate space centered scheme with the ability of minimizing the difference between the exact and numerical dispersion relation equations is proposed. Our emphasis is placed on the accurate modeling of EM waves in the dispersive media of the Debye, Lorentz and Drude types. Through the computational exercises, the proposed dual-preserving Maxwell's equation solver is computationally demonstrated to be efficient for use to predict the long-term accurate wave solutions in a medium belonging either to a frequency independent or to a dependent type.
A new wideband dual-polarized patch antenna consisting of a magnetically-fed and an electrically-fed is presented in the paper. The two feeds are orthogonal to each other at the center of the ground plane and generate 0° and 90° polarization separately. Two pairs of L-shaped slots are etched in the radiating patch to improve the impedance bandwidth. By using a shorting pin connecting the radiating patch to the ground plane, the coupling between the two feeding ports can be reduced. With the help of circuit simulation and full wave simulation, the equivalent circuit model of the antenna is established. The simulated and measured results show that the impedance bandwidths for VSWR less than 2 of the proposed dual-polarized antenna with a profile of are 27.3% (3.29-4.33 GHz) and 19% (3.05-3.69 GHz) for 0° polarization and 90° polarization, respectively, with a height of 0.08 λ0 between radiating patch and ground plane. The measured coupling between the two ports is below -20 dB over the operating band. Moreover, the measured gain of the proposed antenna is about 7.9 dBi and 6.1 dBi for port 1 and port 2, respectively, over the operating band. Measured results of the fabricated antenna prototypes are in good agreement with the simulated results.
A study of UWB on-body communication system performance, with the WiMax off-body electromagnetic interference (EMI) existence, is presented. Firstly, a compact UWB antenna with good on-body performance is verified and chosen as our reference antenna. Using this realistic antenna, channel transfer function (CTF) of UWB on-body channel in an indoor room is investigated by measurements. Based on the measured data, the parameters of its pathloss model and its power delay profile (PDP) model are extracted respectively. Secondly, a new body channel communication system model, composed of the on-body and off-body dual-link channel, together with UWB and WiMax signal models are presented. Finally, UWB on-body communication performances under different WiMax off-body EMI levels are studied by simulation. Simulated results show that this on-body system performance is quite limited and easily affected by the off-body WiMax EMI. It is pointed out that the existing UWB on-body communication abilities should be greatly improved when WiMax off-body EMI signals are considered.
In this paper, a detached zero index metamaterial lens (ZIML) consisting of metal strips and modified split ring resonators (MSRRs) is proposed for antenna gain enhancement. The effective permittivity and permeability of the detached ZIML are designed to synchronously approach zero, which leads the ZIML to having an effective wave impedance matching with air and near-zero index simultaneously. As a result, neither does the detached ZIML need to be embedded in horns aperture nor depends on auxiliary reflectors in enhancing antenna gain, which is quite different from conventional ZIMLs. Moreover, the distance between antenna and the detached ZIML slightly affect the gain enhancement, which further confirms that the ZIML can be detached from antennas. Simulated results show that the effective refractive index of the detached ZIML is near zero in a broad frequency range where the effective relative wave impedance is close to 1. The detached ZIML is fabricated and tested by placing it in front of an H-plane horn antenna. One finds that evident gain enhancement is obtained from 8.9 GHz to 10.8 GHz and the greatest gain enhancement reaches up to 4.02 dB. In addition, the detached ZIML can also work well at other frequencies by adjusting its geometric parameters to scale, which is demonstrated by designing and simulating two detached ZIMLs with center frequencies of 2.4 GHz and 5.8 GHz, respectively.
Spaceborne synthetic aperture radar (SAR) plays more and more important role in Earth observation science, especially with ScanSAR mode which provides wide-swath coverage with moderate resolution. However, scalloping and inter-scan banding (ISB) are two major artifacts, which signicantly degrade the quality of ScanSAR images. In this paper, a novel technique for removal of scalloping and ISB in ScanSAR images is proposed. Scalloping and ISB artifacts are modeled by two-dimensional gain and oset parameters varying as function of both azimuth time and range position. The gain and oset parameters can be split into azimuth and range components. The variations of gain/oset with respect to azimuth and range positions would represent scalloping and ISB artifacts respectively. In the proposed technique, recursive and minimum mean square error (MMSE) estimates of azimuth gain/oset parameters are found out by using Kalman lter for each azimuth location in a subswath by considering corresponding range samples as observation vector. Subsequently, range gain/oset parameters causing ISB artifacts are estimated by using Kalman lter for each range positions by considering azimuth samples as observation vector. The MMSE estimates of gain/oset parameters are used to directly remove scalloping and ISB artifacts. The proposed scheme was applied on simulated as well as calibrated real ScanSAR images. The experimental results exhibited the potential of proposed technique to be used as post processing tool for enhancing ScanSAR image quality.
Three different techniques are applied for accurate constitutive parameters determination of isotropic split-ring resonator (SRR) and SRR with a cut wire (Composite) metamaterial (MM) slabs. The first two techniques use explicit analytical calibration-dependent and calibration-invariant expressions while the third technique is based on Lorentz and Drude dispersion models. We have tested these techniques from simulated scattering (S-) parameters of two classic SRR and Composite MM slabs with various level of losses and different calibration plane factors. From the comparison, we conclude that whereas the extracted complex permittivity of both slabs by the analytical techniques produces unphysical results at resonance regions, that by the dispersion model eliminates this shortcoming and retrieves physically accurate constitutive parameters over the whole analyzed frequency region. We argue that incorrect retrieval of complex permittivity by analytical methods comes from spatial dispersion effects due to the discreteness of conducting elements within MM slabs which largely vary simulated S-parameters in the resonance regions where the slabs are highly spatially dispersive.
The scattering of an arbitrarily oriented dipole field by a circular disk with surface impedance is investigated by using the method of Kobayashi Potential (KP method). The dual integral equations (DIE) are produced during formulation of the problem. The solution of the DIEs is constructed in terms of set of functions which satisfy the boundary conditions as well as required edge conditions. At this stage, we applied the discontinuous properties of Weber Schafheitlins integral and vector Hankel transform. After applying the projection, the resulting expressions are reduced to the matrix equations for the expansion coefficients. The matrix elements are given in terms of the infinite integrals. The far field patterns for the scattered wave are computed for different incident angles, disk sizes and surface impedances for ρ−, Φ− and z−directed dipole field excitation. To validate the results we have obtained the results based on the physical optics approximation and their comparison shows that they quite reasonably match.
Materials that exhibit negative refraction may have many novel applications. We seek to evaluate the possibility of soft-focusing of microwave signals using a medium with an indefinite (hyperbolic) anisotropic permittivity tensor. We fabricated a 147 mm thick and 220 mm wide Styrofoam sample with an embedded array of 12-gauge brass wires of 6.35 mm lattice spacing. Two single-loop antennas were used to approximately generate a transverse magnetic (TM) point source and the associated detector. Using an Agilent 8510C Vector Network Analyzer (VNA), the frequency spectrum was scanned between 7 and 9 GHz. Relative gain or loss measurements were taken at equal spatial steps behind the sample. A scanning robot was used for automatic scanning in the x, y, and z directions, in order to establish the focusing patterns. The signal amplitudes measured in the presence and absence of the sample were compared. The robot was controlled using LabVIEW1, which also collected the data from the VNA and passed it to MATLAB2 for processing. A soft focusing spot was observed when the antennas were placed in two different symmetric configurations with respect to the sample. These results suggest a method for focusing electromagnetic waves using negative refraction in indefinite (hyperbolic) anisotropic materials.
A Transverse Electromagnetic Mode (TEM) cell is one interesting alternative for studies of biological effects of radiofrequency radiation at reduced scale (in vitro studies). Controlled and well-characterized exposure conditions are essential for a concluding investigation: the biological sample has to be exposed to a uniform incident electromagnetic wave and the dose of absorbed radiation has to be precisely determined and correlated with the effect. Unfortunatelly, many times experimental dosimetry is either unavailable or unappliable, so that a pre-characterised and validated experimental set-up is mostly valuable. In this regard, the main objective of present work was to experimentally validate a computational model of an own-built TEM cell designed for bioelectromagnetic experiments in frequency range of 100MHz-1GHz. For validation, three significant parameters were investigated comparatively, by measurements and by computation: scattering parameters; incident electric field distribution; absorbed power in a set of liquid samples. By using the finite integration technique (FIT) method implemented by the commercial code CST Microwave Studio, and by using a vector network analyzer in the experimental approach, we validated the designed TEM cell and characterized it successfully. The second objective was a dosimetric study of four different liquid samples loaded in the cell. We used the absorption coefficient (AC) which may be assimilated to the specific absorption rate (SAR) of energy deposition in the whole sample volume. AC was shown to converge in experiment and simulation up to 800MHz for all samples. AC didn't depend directly upon sample's volume (even if, frequently, greater volumes showed higher absorption) but rather upon the internal field distribution in the sample, distribution that mostly depends on the frequency and on the dimensions of the liquid samples.
This paper investigates the spatial correlation characteristics of multiple antenna arrays deployed in wireless communication systems. First, we derive a general closed-form formula for the spatial correlation function (SCF) of a multiple antenna array with arbitrary array configuration under uniform signal angular energy distribution. Based on this formula, we then explore the characteristics of the SCF for several multiple antenna arrays with different array geometries. It is found that a multiple antenna array with a three-dimensional (3-D) array geometry can reduce the magnitude of its SCF and hence, improve the ergodic channel capacity (ECC) of wireless communication systems. Accordingly, we present a method to find the optimum 3-D antenna array geometry for maximizing the ECC of a wireless communication system. This method develops a novel objective function to incorporate with a particle swarm optimization (PSO) for solving the resulting optimization problem. Simulation results are provided for confirming the validity and the effectiveness of the proposed method.
We consider the performance analysis of natural frequency-based radar target recognition in the frequency domain. Based on the probability density function (PDF) of some quantity consisting of the projections of the frequency response onto the column spaces of the matrices constructed using the natural frequencies of the specific targets, we propose to analytically calculate the probability of the correct classification, where the PDF is obtained from the inverse Fourier transform of the characteristic function. The scheme is validated by comparing the performance using the analytic method with that using the Monte-Carlo simulation.
The purpose of this paper is to provide both qualitative and quantitative assessment of one of the methods for providing reliable transmission in the ZigBee system. After intensive research on the time delay spread in a variably loaded reverberation chamber, this facility was then used to measure the Packet Error Rate under multipath conditions ranging from an unloaded to an overloaded chamber case. In all measurements, the key parameter was the number of allowed packet repetitions (retries). Eventually, recommendations were given regarding the optimal use of retries and their impact on ZigBee performance under different multipath scenarios obtained in the reverberation chamber and related to particular propagation environments to which these conditions are typical.
A novel imaging technique based on a frequency scanning antenna array is presented. The method is conceived to provide angular information in range-based radar systems which do not allow mechanical or electronic beam steering. The beam steering is changed with the frequency, which requires a novel scattered field data processing scheme/algorithm to recover the SAR image. System features, advantages and limitations are discussed, presenting simulation and measurement results which show the system capabilities to resolve the range and angular position of the objects.
Due to growing importance of wireless access and the steeply growing data volumes being transported, the power consumption of wireless access networks will become an important issue in the coming years. This paper presents a model for this power consumption and investigates three base station types: macrocell, microcell, and femtocell base stations. Based on these models, the coverage effectiveness of the three base station types is compared and the influence of some power reducing techniques such as sleep modes and MIMO (Multiple Input Multiple Output) is evaluated.
This paper addresses the problem of designing statistical features for the extraction of building-up areas (BAs) from highresolution polarimetric synthetic aperture radar (PolSAR) imagery. The idea is to represent a building-up area by the distribution of its mid-level components, called intermediates, which are statistical patterns unsupervisedly learnt from PolSAR images. More precisely, by analyzing the structural properties and the polarimetric characteristics exhibited in various terrain types, we propose two kinds of midlevel features for small regions: the cluster based statistical feature (CSF) and the scattering mechanism based statistical feature (SMSF). In detail, for the CSF, the intermediates are the K-mean clusters with Wishart distance of the PolSAR images; for the SMSF, the intermediates are the scattering mechanism categories obtained by relying on a four-component decomposition with deorientation of the PolSAR images. In contrast with existing features for describing BAs, the proposed features, i.e., CSF and SMSF, capture more complex context information of BAs. We compare the proposed features with those based on the Gaussian Markov random field (GMRF) models, which have been proven to be suitable for BAs mapping. Experimental results on RADARSAT-2 datasets demonstrate the effectiveness of the proposed features.
In this work, a sub-millimeter wave frequency scanning 8 x 1 element antenna array is presented for its use in a terahertz imaging system operating in the 220-330 GHz frequency band. The antenna array is formed by eight open ended waveguides, a phase-shifting network implemented with WR-3 rectangular waveguides and a power divider. Dielectric rods are used to improve the radiation patterns at large beam-steering angles. Prototypes of antenna arrays with and without the dielectric rods have been manufactured and experimentally characterized. A beam-steering range greater than 40° has been obtained for a frequency sweep between 270 GHz and 330 GHz.
This paper proposes a novel nano-sinusoid particle to be employed in enhanced localized surface plasmon resonance (LSPR) bio-sensing devices. Numerical investigations are carried out to demonstrate advantages offered by the proposed nano-particle on LSPR enhancement over other nano-particles including noble nano-triangles and nano-diamonds. Although nano-triangles exhibit high concentration of the electric field near their tips, when illuminated with a light polarized along the tip axis, they present only one hot spot at the vertex along the polarization direction. To create a structure with two hot spots, which is desired in bio-sensing applications, two nano-triangles can be put back-to-back. Therefore, a nano-diamond particle is obtained which exhibits two hot spots and presents higher enhancements than nano-triangles for the same resonant wavelength. The main drawback of the nano-diamonds is the fluctuation in their physical size-plasmon spectrum relationships, due to a high level of singularity as the result for their four sharp tip points. The proposed nano-sinusoid overcomes this disadvantage while maintaining the benefits of having two hot spots and high enhancements.
We study the propagation of waves on infinite and finite size arrays made of subwavelength magnetoelectric resonators. We propose an analytical study where each magnetoelectric resonator is modelled simultaneously by an electric and a magnetic dipole. We show how near field coupling and wavenumber quantification due to the finite size of the structure induce a frequency splitting of the resonator fundamental mode. We theoretically demonstrate that despite a spatial period of the waves smaller than half wavelength (in vacuum), the structure can efficiently emits radiations. An analytic expression of the Q factor associated to the radiation losses is proposed. To correctly estimate this factor, we show that not only near but also far field interaction terms between the dipoles must to be considered.
In this work, a new method has been proposed for the finite-difference time-domain (FDTD) analysis of the transient grounding resistance (TGR) of large grounding systems. To calculate the TGR, a coarse grid has been occupied to model the earthing conductor, the CPML is chose to truncate the computational domain, and parallel implementation is involved to overcome the memory limit of the serial FDTD. With this model, the effect of the earthing conductor number and topology structure, the buried depth, and the ground permittivity and conductivity on the TGR is tested to find an optimized program to decrease the TGR of the lightning protection grounding systems.
We numerically studied the spectrum of Cherenkov optical radiation by a nonrelativistic anisotropic electron bunch crossing 3D dispersive metamaterial. A practically important case when such a medium is described by Drude model is investigated in details. In our theory only parameters of a metamaterial are fixed. The frequency spectrum of internal excitations is left to be defined as a result of the numerical simulation. It is found that a periodic field structure coupled to plasmonic excitations is arisen when the dispersive refractive index of a metamaterial becomes negative. In this case the reversed Cherenkov radiation is observed.
Electromagnetic (EM) eigen modes in a fishnet metamaterial (MM) slab have been comprehensively analyzed in an experimental configuration, based only on precise solutions of Maxwell equations. The EM eigen modes were directly detected from light-absorption peaks. Each mode was explicitly characterized by the dispersion diagram and EM field distributions. It was consequently found that the modes were classfied into either inner modes inside the slab or a mode at the interface with the surrounding media. The symmetric properties of the inner modes were clarified using group theory. The interface mode was found to come from surface plasmon polariton at flat metal/insulator interface. The present analysis procedure is generally applicable to MM slabs and enables to clarify the properties without models or assumptions, which have been usually used in MM studies.
The paper proposes a Composite Right/Left Handed double periodic transmission line structure with both inductance and capacitance loaded. The structure exhibits leaky wave radiation and hence can be considered for LWA applications. We have theoretically obtained dispersion characteristics using Singular perturbation method. Also, the radiation efficiency has been obtained for different modulation indices. A novel leaky wave radiation has been obtained below the left handed passband with narrow bandwidth. The proposed structure has been fabricated on FR4 substrate and measured. The simulated and measured results seem to be in good agreement.
Over the last few years, the active and growing interest in Radiofrequency Identification (RFID) technology has stimulated a conspicuous research activity involving design and realization of passive label-type UHF RFID tags customized for specific applications. In most of the literature, presented and discussed tags are prototyped by using either rough-and-ready procedures or photolithography techniques on rigid Printed Circuit Boards. However, for several reasons, such approaches are not the most recommended, in particular they are rather time-consuming and, moreover, they give rise to low quality devices in one case, and to cumbersome and rigid tags in the other. In this work, two alternative prototyping techniques suitable for cost-effective, time-saving and highperformance built-in-lab tags are introduced and discussed. The former is based on the joint use of flexible PCBs and solid ink printers. The latter makes use of a cutting plotter to precisely shape the tag antenna on thin copper sheets. Afterwards, a selection of tags, designed and manufactured by using both traditional and alternative techniques, is rigorously characterized from the electromagnetic point of view in terms of input impedance and whole tag sensitivity by means of appropriate measurement setups. Results are then compared, thus guiding the tag designer towards the most appropriate technique on the basis of specific needs.
In this paper, the experimental validation of a time domain reflectometry (TDR)-based method for pinpointing water leaks in underground metal pipes is presented. The method relies on sensing the local change in the dielectric characteristics of the medium surrounding the leak point. The experimental validation of the method was carried out through measurements performed on a pilot plant (experimental case P1) and through on-the-field measurements performed on two `already-installed pipes', i.e., already operating and connected to the water distribution system (experimental cases P2 and P3). For the pilot plant, different leak conditions were imposed and the corresponding TDR responses were acquired and analyzed. For the onthe-field measurements, TDR measurements were performed on pipes for which a leak-detection crew had preliminarily individuated the possible presence of leaks (through traditional leak-detection methods). Finally, in view of the practical implementation of the proposed TDR-based leak-detection system, a data-processing procedure (which gives an automatic evaluation of the position of the leak) is also presented.
Electromagnetic energy harvesting holds a promising future for energizing low power electronic devices in wireless communication circuits. This article presents an RF energy harvesting system that can harvest energy from the ambient surroundings at the downlink radio frequency range of GSM-900 band. The harvesting system is aimed to provide an alternative source of energy for energizing low power devices. The system design consists of three modules: a single wideband 377 Ω E-shaped patch antenna, a pi matching network and a 7-stage voltage doubler circuit. These three modules were fabricated on a single printed circuit board. The antenna and Pi matching network have been optimized through electromagnetic simulation software, Agilent ADS 2009 environment. The uniqueness of the system lies in the partial ground plane and the alignment of induced electric field for maximum current flow in the antenna that maximizes the captured RF energy. The design and simulation of the voltage doubler circuit were performed using Multisim software. All the three modules were integrated and fabricated on a double sided FR 4 printed circuit board. The DC voltage obtained from the harvester system in the field test at an approximate distance of 50 m from GSM cell tower was 2.9 V. This voltage was enough to power the STLM20 temperature sensor.
A matrix splitting domain decomposition method based on hybrid shell vector element-boundary integral (MSDD-SVE-BI) for three dimensional electromagnetic scattering from multiple conducting bodies coated by thin layer dielectric is proposed. In the framework of domain decomposition, the whole computational domains are divided into a lot of sub-SVE-domains and boundary element domains. For conducting body coated with thin-layer dielectric, the shell vector element is used instead of traditional tetrahedral elements to reduce the number of unknowns. Further, a block Gauss-Seidel type pre-conditioner is applied to attain fast matrix splitting formulation for the matrix connecting surface electric field and surface magnetic field. By this method, only sub-matrix inversion is required in the SVE-BI method, the computational time for connecting matrix can be reduced greatly. Several numerical examples prove the accuracy and efficiency of the present method.
A new metamaterial topology is proposed, based on dielectric coated spheres. The effect of the coating is an increased negative permittivity and permeability bandwidth compared with the non-coated spheres. The influence of the dimensional parameters is analyzed, and the relation of each of them with the bandwidth is studied. The theoretical results are confirmed by full wave simulations using CST. A combination of the new topology with wires is used to reach an NRI bandwidth of about 23%. To the knowledge of the authors, to date this is the highest bandwidth reported in literature.