Guided-Mode Resonance (GMR) effects in transparent periodic gratings possess a number of remarkable phenomena. GMRs exhibit strong features in the optical spectrum, i.e. dips, peaks, cusps, and may attain extremely high Q-factors. In some cases resonant reflection with the efficiency equal to unity can be observed. We demonstrate that the introduction of small losses in the structure can drastically modify its optical response by causing strong absorption resonances. Unity reflection in loss-free structures can be almost completely converted into unity absorption peaks as soon as very small losses are introduced. Even thin absorbing films in the structure (or in its vicinity) can lead to such strong resonant absorption effects. The resonances may exhibit a negligible spectral shift, but a significant variation in the magnitude when losses are slightly altered, which is highly attractive for sensor and switch applications. Absorption peaks experience a resonant behavior with respect to both frequency and material losses. We show that the width of the absorption peaks decreases and approaches the width of the reflection peaks, as losses decrease. Thus, high-Q resonances can be observed. The absorption resonances also possess strong angular dependence; they may split and significantly increase in magnitude for a slightly inclined incidence. We elucidate the resonant reflection/absorption effects theoretically and provide numerical examples.
A new balanced dual-band bandpass filter with strong commonmode rejection is presented in this paper. Common-mode rejection is provided by a section of a periodic microstrip differential line that behaves as a low-pass filter under common-mode operation. In contrast, the differential line exhibits very good all-pass behavior under differential mode operation. This structure is combined with a differential dual-band bandpass filter based on embedded resonators. Simulations and experiments confirm that the combined structure has good common-mode rejection within the passbands of the dual-band differential filter.
A new circuit and technique to extend bandwidth performance while preserving improvement on efficiency performance over the one attainable by conventional distributed amplifier (DA) is presented. The theoretical analysis is described in detail, and a test vehicle is realized to demonstrate the effectiveness of the proposed method. Output power of ~29 dBm, gain of 10 dB, covering a bandwidth from 100 to 800 MHz, PAE of 20-45% is experimentally demonstrated. The result is compared with measured result of conventional DA, a significant improvement of bandwidth and efficiency are achieved.
This paper presents a multilevel Model Order Reduction technique for a 3-D electromagnetic Finite Element Method analysis. The reduction process is carried out in a hierarchical way and involves several steps which are repeated at each level. This approach brings about versatility and allows one to efficiently analyze complex electromagnetic structures. In the proposed multilevel reduction the entire computational domain is covered with macro-elements which are subsequently nested, in such a way that size of the problem which has to be reduced at each level is relatively small. In order to increase the speed of the reduction at each level, the electric field at the macro-elements' boundaries is projected onto the subspace spanned by Legendre polynomials and trigonometric functions. The results of the numerical experiments confirm the validity and efficiency of the presented approach.
This paper deals with the problem of constant false alarm rate (CFAR) target detection in high-resolution ground synthetic aperture radar (SAR) images based on KK distribution. For the parameter estimation of KK distribution, the semi-experiential algorithm is analyzed firstly. Then a new estimation algorithm based on the particle swarm optimization (PSO) is proposed, which takes the discrepancies between the histogram of the clutter data and probability density function (PDF) of KK distribution at some selected points as the cost function to search for the optimal parameter values using PSO algorithm. The performance of the two algorithms is compared using Monte-Carlo simulation using the simulated data sets generated under different conditions; and the estimation results validate the better performance of the new algorithm. Then the KK distribution, which is proposed for spiky sea clutter originally, is applied to model the real ground SAR clutter data. The goodness-of-fit test clearly show that the KK distribution is able to model the ground SAR clutter much better than some common used model, such as standard K-distribution and Gamma, etc. On this basis, a global CFAR target detection algorithm is presented. The detection threshold is calculated numerically through the cumulative density function (CDF) of KK distribution. Comparing the amplitude of every SAR image pixel with this threshold, the potential targets in ground SAR images can be located effectively. Then target clustering is implemented to eliminate the false alarm and obtain more accurate target regions. The detection results of the proposed algorithm in a typical ground SAR image show that it has better performance than the detector based on G0 distribution.
To analyze and to handle the radio frequency immunity of microcontrollers requires understanding the origins of the complex frequency response of the immunity. This paper assumes that the frequency response of the immunity can be characterized with a set of fingerprint features in the immunity curves. Positions and shapes of those fingerprint features are determined by certain components in the disturbance propagation network. In order to prove that assumption, a series of models are created and simulated. The roles of various model components on the immunity are analyzed by comparing the simulation results from different model structures. The fingerprint features on the immunity curves are identified. The paper shows how to treat a wide-range immunity curve with separated features. It also shows the responsible model components for those separated features. With the awareness of those features and their origins, researchers can concentrate on extracting the models of the most important components in the disturbance propagation network when modeling the immunity of the complex integrated circuits like microcontrollers.
This paper presents a novel artificial neural network (ANN) model estimating vehicle-level radiated magnetic emissions of an electric car as a function of the corresponding driving pattern. Real world electromagnetic interference (EMI) experiments have been realized in a semi-anechoic chamber using Renault Twizy. Time-domain electromagnetic interference (TDEMI) measurement techniques have been employed to record the radiated disturbances in the 150 kHz-30 MHz range. Interesting emissions have been found in the range 150 kHz-3.8 MHz approximately. The instantaneous vehicle speed and acceleration have been chosen to represent the vehicle operational modes. A comparative study of the prediction performance between different static and dynamic neural networks has been done. Results showed that a Multilayer Perceptron (MLP) model trained with extreme learning machines (ELM) has achieved the best prediction results. The proposed model has been used to estimate the radiated magnetic field levels of an urban trip carried out with a Think City electric car.
We analyze the performance of finite-difference time-domain (FDTD) method implementations for 2D and 3D problems. Implementations in Fortran, C and C++ (with Blitz++ library) languages and performance tests on several hardware setups (AMD, Intel i5, Intel Xeon) are considered. The performance of implementations using traditional FDTD algorithm for the largest size of test problem is limited by the bandwidth of computer random-accessed memory (RAM). Our implementations are compared with a commercial simulation software package Lumerical FDTD Solutions and an open source project Meep.
The paper deals with the propagation of electromagnetic waves through twisted clad dielectric optical fibers. The structure of these fibers is analogous to travelling wave tubes used in microwave devices, and the usefulness would be in the areas of optical sensing. This is because the twists in fiber would be affected due to the imposed stress and/or strain, leaving thereby the possibility to alter the propagation characteristics. A rigorous analytical investigation has been carried out with the emphasis on the energy flux density patterns due to the different propagating modes in the fiber. The dispersion relations of the system are deduced and the energy flux densities are evaluated under different pitch angles of twist. The effect due to conducting helix pitch on the electromagnetic wave propagation is emphasized.
A compact multilayer substrate integrated waveguide (SIW) dual-mode filter with multiple transmission zeros for high-selectivity application is presented. By introducing mixed coupling between source and load, the proposed filter could have four transmission zeros which can be controlled flexibly. Owing to the multilayer structure, the proposed filter occupies similar area in comparison with conventional dual-cavity dual mode SIW filters, but exhibits better frequency selectivity. An experimental filter with a center frequency of 10 GHz is designed using low temperature co-fired ceramic (LTCC) technology to validate the proposed structure, and measured results agree well with simulated ones.
The Polar Format Algorithm (PFA) is suitable for spotlight synthetic aperture radar (SAR) image focusing either in monostatic or bistatic cases. The classic linear-trajectory PFA complete data correction in wavenumber domain, converting data from the polar format to the rectangular format. However, the two-dimension processing (either using interpolation or chirp-z transform) introduces heavy computational load, which limits its real-time applications. This study presents a conical-trajectory PFA for bistatic SAR, in which the transmitter and receiver are designed to fly on conical surfaces, to simplify image formation procedures via eliminating the necessity of range processing. Moreover, the conical-trajectory PFA provides a space-invariant range resolution to simplify the SAR image comprehension. A spotlight forward-looking bistatic missile guidance application was simulated for the algorithm validation and performance analysis.
A satellite-borne frequency selective surface (FSS) for atmospheric sensing application is presented. This brand new type of band-pass filter has an operating frequency at 183 GHz, which is a typical frequency on H2O absorption line. Comprising an ultra-thin gilding layer and a SiO2 substrate layer, this complex periodic component exhibits an extremely low insertion loss (< 0.22 dB) and high isolation (> 20 dB) between closely spaced frequency channels of 45° incident wave. Periodic Method of Moment (PMM) approach is applied to determine the initial geo-metrical parameters of FSS unit cell, and the optimization approach based on the Genetic Algorithm (GA) enables us to obtain the requisite spectral response and transmission characteristics for both TE and TM polarization. The experimental results show that the proposed PMM-GA technique is effective for analyzing space-borne FSS at millimeter wave range.
This paper illustrates an explicit multiresolution time-domain (MRTD) scheme based on Daubechies' scaling functions with a spherical grid for time-domain Maxwell's equations. The stability and dispersion property of the scheme are investigated and it is shown that larger cells decrease the numerical phase error, which makes it significantly lower than FDTD for low and medium discretizations. Moreover, this technique is applied to the modeling of an air-filled spherical resonator, and numerical results demonstrate the effectiveness of the proposed algorithm.
A hybrid tuning method for microwave filters is presented in this paper. This novel tuning technique is based on the combination of the Cauchy method and aggressive space mapping (ASM) technique. Cauchy method is applied to determine the characteristic polynomials of the filter's response, then the parameters (coupling matrix) of the low-pass prototype is extracted from the characteristic polynomials. The aggressive space mapping is used to optimized the fine model to guarantee that each step of a tuning is always in the right direction. The validity is verified by two examples. One deals with the four-resonator cross-coupled filter and the other one is an direct coupled six-resonator filter.
A cylindrical microstrip array antenna with 5 pairs of coupled slotted strip framed patches is analyzed. The patches are proximity-fed by a cylindrical microstrip line. In order to extract the reflection coefficient from the standing wave pattern on the microstrip line, its length is about 5 wavelengths. To the best of the authors' knowledge proximity-fed cylindrical arrays have not been analyzed before using a rigorous MOM model that takes into account all electromagnetic couplings between patches and feeding line. The paper consists of three parts. The first part describes a plane wave excitation of the cylindrical microstrip structure. It introduces some innovating theoretical developments, like the improvement of the asymptote for the spectral Green's function and the explicit surface wave contribution. The second part calculates the radar cross section of the cylindrical microstrip structure with single and coupled slotted strip framed patches. The resonant frequencies, and the amplitude and phase of the current distribution are analysed. The third part describes a design for a proximity-fed array of 5 coupled slotted strip framed patches. It gives the reflection coefficient, current distribution on the patches, and radiation pattern. A very low level of cross polarization (< -40 dB) is achieved. It is shown that the resonant frequencies of the cylindrical array and its planar analogue lie very close to each other. This is due to the common nature of the low frequency slot resonance for the slotted strip framed patch.
Radio frequency (RF) dielectric heating was tested to control Cryptolestes ferrungineus S. in the bulk wheat samples (ca.152 g, dia. = 50 mm, ht.= 100 mm) at the MCs (%, w. b.) of 12, 15, and 18 using a pilotscale RF heater (1.5 kW, 27.12MHz) in the batch mode. When the temperature of the hottest spot (geometric center) of the sample, TH was at 80°C, all the adult insects were found dead at the cold spots, near bottom-wall, at 50.7°C to 56.0°C depending up on the wheat MCs. The temperatures of the insect-slurries higher than that of the bulk wheat by 0.8°C to 15.1°C indicated the selective heating of the insects. The mortalities of adult insects were almost constant within the quarantine period, QP1 (5 wk). The elapsed time during QP1 had a significant effect only on the insects' mortalities with the wheat at 12% MC. The wheat MC had only marginal significance on the absolute mortalities of insects. The larvae were completely destroyed at temperatures between 55°C and 60°C. The complete mortality of all life stages (eggs, larvae, pupae, and adults) of the insect was achieved at TH = 80°C without any emergence of the insects during QP2 (8 wk). The RF treatment enhanced the germination of the wheat kernels at 12% MC while it was decreased by 2% to 33% depending up on the wheat MC, and the treatment temperature. Temperature had no significant effect on the falling numbers, and the yields of flour, bran, and shorts, and the peak-bandwidth and the MC of the wheat, and the flour protein values. The means of the mixing-development-time deferred from the controls mostly for the wheat at 15% MC and TH = 70°C, and 18% MC and TH = 70°C and 80°C. The mean-peak-height and the color values varied between 4% and 16%, and 3% and 6% off the controls depending up on the temperatures. The uniform temperature of 60°C should be enough to control all life stages of the insect completely with a little or no changes in the important product quaities and germination of the wheat at MCs safe for the storage. Future research mainly focused on better estimation of the insect-to-grain electric field intensities is essential.
The knowledge of amplitude and location of sliding scattering centers is necessary for low detectable streamlined targets in many applications, such as precise estimation of shape or velocity of targets, and also target tracking and recognition. Based on the thorough analysis of scattering characteristics, the scattering center features of streamlined targets are presented which demonstrate the dependence of location and amplitude on the target orientation relative to the radar. Then based on these features, an accurate scattering center model for streamlined targets is proposed. The parameters of this model is estimated by genetic algorithm, and then the given model with estimated parameters is validated by full wave numerical method allowing precise backscattered data computation.
In this paper, applications of the discrete Green's function (DGF) in the three-dimensional (3-D) finite-difference time-domain (FDTD) method are presented. The FDTD method on disjoint domains was developed employing DGF to couple the subdomains as well as to compute the electromagnetic field outside these subdomains. Hence, source and scatterer are simulated in separate subdomains and updating of vacuum cells, being of little interest from a user point of view, can be avoided. In the developed method, the field radiated by a single subdomain is computed as a convolution of DGF with equivalent current sources measured over two displaced Huygens surfaces. Therefore, the computed electromagnetic field is compatible with the FDTD grid and can be applied as an incident wave in a coupled total-field/scattered-field (TFSF) subdomain. In the developed method, the DGF waveforms are truncated using the Hann's window and windowing parameters assuring accuracy of computations are pointed out. The error of the field computations varies between -90 dB and -40 dB depending on the DGF length and excitation waveform. However, if the DGF length is equal to the number of iterations in a simulation, the presented DGF applications return the same results as the direct FDTD method.
Due to the increased use of indoor wireless networks and the concern about human exposure to radio-frequency sources, exposure awareness has increased during recent years. However, current-day network planners rarely take into account electricfield strengths when designing networks. Therefore in this paper, a heuristic indoor network planner for exposure calculation and optimization of wireless networks is developed, jointly optimizing coverage and exposure, for homogeneous or heterogeneous networks. The implemented exposure models are validated by simulations and measurements. As a first novel optimization feature, networks are designed that do not exceed a user-defined electric-field strength value in the building. The influence of the maximally allowed field strength, based on norms in different countries, and the assumed minimal separation between the access point and the human are investigated for a typical office building. As a second feature, a novel heuristic exposure minimization algorithm is presented and applied to a wireless homogeneous WiFi and a heterogeneous WiFi-LTE femtocell network, using a new metric that is simple but accurate. Field strength reductions of a factor 3 to 6 compared to traditional network deployments are achieved and a more homogeneous distribution of the observed field values on the building floor is obtained. Also, the influence of the throughput requirement on the field strength distribution on the building floor is assessed. Moreover, it is shown that exposure minimization is more effective for high than for low throughput requirements and that high field values are more reduced than low field values.
Based on the Propagation-Inside-Layer Expansion (PILE) and the Forward-Backward method (FBM), the composite scattering from the target below a dielectric rough soil surface using the extended PILE (EPILE) combined with the Forward-Backward method (FBM) is studied. The accuracy and efficiency of the EPILE+FBM for this specific type of composite scattering is researched by comparing with the method of moments (MOM), the influences of the target size, target depth, target horizontal distance, the rms height, the correlation length, the incident angle and the soil moisture content, etc, to the bistatic scattering coefficient (BSC) are also investigated.
The hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) is a powerful method for calculating scattering by inhomogeneous objects. However, the conventional FE-BI-MLFMA often suffers from iterative convergence problems. A non-overlapping domain decomposition method (DDM) is applied to FE-BI-MLFMA to speed up the iterative convergence. Furthermore, a preconditioner based on absorbing boundary condition and symmetric successive over relaxation (ABC-SSOR) is constructed to further accelerate convergence of the DDM-FE-BI-MLFMA. Numerical experiments demonstrate the efficiency of the proposed preconditioned DDM-FE-BI-MLFMA.
A novel multi-state RF MEMS switch for microstrip antenna applications is presented. The proposed switch exhibits seven different states of operation, has a very simple DC biasing mechanism and can be integrated with antenna structure. Based on these properties, this switch may find its usage in multifunction reconfigurable antennas. To exhibit this application, it is employed in the reconfiguration mechanism of a U-slotted antenna. In different states of the switch, the antenna resonates at different frequencies. All the standard frequency bands of the wireless communication services with some additional frequency bands is covered with this reconfigurable U-slotted antenna. Moreover, the proposed antenna structure is a cost-effective solution since it comprises a commonly used FR4 substrate. The switch is integrated with antenna structure on the same substrate. A prototype of the designed antenna was fabricated and tested for performance verification of the proposed switch and antenna.
The range profile (RP) of an automobile is derived by compressing the wideband radar signal, and it can be utilized for the classification and thus contribute to lane change and collision avoidance. However, the limited radar bandwidth due to the cost and the system complexity impedes the successful classification. This paper proposes an efficient method to construct an efficient feature vector of the automobile RP through combined use of the central moment, the information on the maximum-minimum and the peak information. Simulation results using the five automobile models composed of point scatterers and a simple nearest neighbor classifier prove that the proposed method improves the classification result, especially in the multi-aspect classification.
This paper proposes a coupling model of the Quasi-Continuous High Magnetic Field (QCHMF) systems that incorporates the electrical, thermal and mechanical dynamics of the magnet system and the power supply system. The design of QCHMF systems is formulated as a five-objective optimization problem and a scoring system based on preference of the designer is adopted to classify the Pareto points of the optimization problem. An optimized mono-coil 50 T/100 ms QCHMF system is designed with a 67.5 MW rectifier of the Wuhan National High Magnetic Field Center (WHMFC), which is taken as an example to verify the proposed model and optimization method. Detailed simulation models of the optimized QCHMF system are built in Matlab and Comsol and the results agree well with the designed technical specifications. The proposed model and optimization method are generic which can be applied to other QCHMF systems with minor modifications.
When using ultra-wide band (UWB) radar to detect targets in various conditions, identifying whether the target buried under building debris or in bad visibility conditions is a human or an animal is crucial. This paper presents the application of the wavelet entropy (WE) method to distinguish between humans and animal targets through brick wall and in free space at a certain distance. In the study, WE, WE change, and WE of the related range points were estimated for the echo signals from five humans and five dogs. Our findings indicate that the entropy or degree of disorder in the energy distribution of the human target was much lower than that of the dog, and the waveform of the human's entropy was smoother than that of the dog. In addition, the body micro motions of humans are much more ordered than those of dogs. WE can be employed as a quantitative measure for recognizing invisible targets and may be a useful tool in the UWB radar's practical applications.
This paper analyzes the azimuth spectrum folding problem which arises from the dependence of the Doppler centroid on range frequency in squinted spotlight synthetic aperture radar (SAR). Based on the analysis, a novel approach for squinted spotlight SAR is proposed in this paper. In this approach, an azimuth preprocessing step including a deramping operation and an operation of azimuth spectrum replicating and filtering is introduced to eliminate spectrum folding problem. Then, a modified Range Migration Algorithm (RMA) is adopted to process the preprocessed data. This approach extends the focusing capacity of traditional two-step processing approach from broadside spotlight SAR to squinted case. Moreover, this approach is e±cient due to a limited azimuth data extension to resolve the spectrum aliasing problem. Experimental results on simulated raw data validate the proposed approach.
A novel compact microstrip-fed planar monopole antenna with quad-notched bands is presented. The proposed antenna is based on one rectangular-stepped-patch. To achieve the higher resonance over the 12 GHz, one lateral L-shaped structure is embedded in the ground. By inserting four U-shaped slots in the radiation patch, quad band-notched properties in the WiMAX (3.3-3.6 GHz), INSAT(4.5-4.8 GHz), lower WLAN (5.15-5.35 GHz) and higher WLAN (5.725-5.825 GHz) are obtained. Experimental results indicate that the designed UWB antenna can obtain broadband matched impedance values, good frequency selectivity over the notched bands, relatively flat group delay and nearly omni-directional transmission characteristics across the UWB frequencies. More importantly, the quad-notched bands can be reconfigurable by shorting the corresponding U-shaped slots.
In this paper, a novel power divider integrated with substrate integrated waveguide (SIW) and defected ground structures (DGS) techniques is proposed to provide both power dividing and filtering functions. The SIW technique holds advantages of low profile, low-lost, mass-production, easy fabrication and fully integration with planar circuits. By integrating with defected ground structures (DGS) technique, the size and cost of system can be effectively reduced as the proposed power divider has a function of filtering which leads to reduction of one filter. In order to verify the design approach, the proposed power divider with equal power divisions at the center frequency of 8.625 GHz is fabricated and measured. The measured results demonstrate that the insertion loss is less than 1.2 dB and the input return loss less than 16 dB across the bandwidth of 1.4 GHz (FBW is 16%). Moreover, the imbalances of the amplitude and phase are less than 0.3 dB and 0.5 degree, respectively.
We systematically study the Cherenkov optical emission by a nonrelativistic modulated source crossing 3D dispersive metamaterial. It is found that the interference of the field produced by the modulated source with the periodic plasmonic-polariton excitations in a metamaterial leads to the specific interaction in the frequency range where the dispersive refractive index of a metamaterial is negative and the reversed Cherenkov emission is generated. Such resonance considerably modifies the spatial structure of the Cherenkov field. In our study parameters of a metamaterial and modulated source are fixed while the frequency spectrum of the plasmonic excitations is formed due to the fields interplay in the frequency domain.
A novel inductively loaded monopole for current and future ultra-wide-band (UWB) applications is presented. The antenna is compact and of small size (16 mm×20 mm×0.8 mm), and offer a very simple geometry suitable for low cost fabrication and straightforward printed circuit board integration. More specifically, the impedance matching of the classic printed loop loaded monopole is improved by employment of the tapered microstrip feed line between K-connector and the printed monopole. By using this technique, impedance bandwidth (S11 < -10 dB) from 3.03 GHz to over 40 GHz is obtained. Measured and simulated return losses curves are provided along with radiation patterns and gain, as a function of frequency. Compared to the recently reported UWB antennas, the presented antenna have smallest size, widest bandwidth, and simple configuration to realize the application in current and future UWB communication systems. Furthermore, a symmetric radiation patterns and satisfactory gain make the presented antenna a suitable candidate for practical UWB applications.
Due to the increasing number of applications in engineering design and optimization, more and more atention has been paid to full-wave simulations based on computational electromagnetics. In particular, the finite-element method (FEM) is well suited for problems involving inhomogeneous and arbitrary shaped objects. Unfortunately, solving large-scale electromagnetic problems with FEM may be time consuming. A numerical scheme, called the dual-primal finite element tearing and interconnecting method (FETI-DPEM2), distinguishes itself through the partioning on the computation domain into non-overlapping subdomains where incomplete solutions of the electrical field are evaluated independently. Next, all the subdomains are ``glued'' together using a modified Robintype transmission condition along each common internal interface, apart from the corner points where a simple Neumann-type boundary condition is imposed. We propose an extension of the FETI-DPEM2 method where we impose a Robin type boundary conditions at each interface point, even at the corner points. We have implemented this Extended FETI-DPEM2 method in a bidimensional configuration while computing the field scattered by a set of heterogeneous, eventually anistropic, scatterers. The results presented here will assert the efficiency of the proposed method with respect to the classical FETI-DPEM2 method, whatever the mesh partition is arbitrary defined.
In this paper, a novel circular-hexagonal fractal antenna is investigated for super wide band applications. The proposed antenna is made of iterations of a hexagonal slot inside a circular metallic patch with a transmission line. A partial ground plane and asymmetrical patch toward the substrate are used for designing the antenna to achieve a super wide bandwidth ranging from 2.18 GHz to 44.5 GHz with bandwidth ratio 20.4 : 1. The impedance bandwidth and gain of the proposed antenna are improved than the recently reported antennas which make it appropriate for many wireless communications systems such as ISM, Wi-Fi, GPS, Bluetooth, WLAN and UWB. Details of the proposed antenna design are presented and discussed.
In this paper, some optimal programs have been proposed through the analyses of transient grounding resistance (TGR) to reduce the grounding resistance using the finite-difference time-domain method. First, the TGR of various electrode types, lengths and sectional programs is studied, and it is found that a flat bar is the most financially efficient conductor to be used as grounding electrode. Enlarging grounding electrode length can reduce grounding resistance when it is shorter than the effective length, but the reduction effect declines as the length increases. Additionally, a series of small electrodes would lead to a much lower resistance than a single large one. Second, it is demonstrated that locally improving the soil near the grounding system is an efficient way of reducing the grounding resistance. Improving a limited area soil surrounding the lifting line would reduce the peak resistance significantly, while local enlarging electrodes surrounded soil conductivity can reduce the grounding system steady resistance obviously.
Electromagnetic interference (EMI) of the power supply system in electric vehicles will seriously affect the safety of the vehicle and passengers' health. So a model of power supply system is presented to analyze its conducted EMI in the paper. This model shows the effects of paralleled interleaving DC/DC converter, which contains the new circular current EMI characteristics. Also, a novel power battery model is established considering both the energy dynamic processes and the high frequency features. Firstly, the power electronics devices are studied as the most important part of the DC/DC converter. Then, the equivalent model of the paralleled interleaving DC/DC converter is set up to express the interference source features. Also, the power battery, which is the main energy storage equipment in electric vehicles, is modeled as EMI propagation paths. Furthermore, loads of the power supply system, such as lead acid battery and low voltage devices, are investigated to evaluate their immunity. Finally, the system model is established. The system EMI is analyzed to get their generating causes, time domain and frequency domain characteristics based on both simulations and experiments.
The utility of slotted waveguide antennas would be maximized if the bandwidth of the radiating elements matched that available in the waveguide. This was achieved using a spiral shaped slot cut through the broad-wall of a rectangular waveguide. The predicted total efficiency and peak realized gain were relatively uniform across the entire bandwidth. The current distribution around the slot was predicted to be similar to that around a conventional, center fed, slot spiral antenna, indicating similarity of radiation mechanisms. Finally, the antenna patterns for spiral shaped slots in waveguides manufactured from copper and carbon fibre reinforced polymer (CFRP) were shown to be similar to that predicted.
Tape-helix transmission lines and helical coils have important applications in communication technology, signal measurement, pulse delay, pulse forming and antenna technology. In this paper, a set of fully dispersive propagation theory based on matrix method is firstly introduced to explain the propagation characteristics of travelling electromagnetic waves in multiple stages of helical Blumlein transmission lines with finite lengths. The different stages of helical transmission lines are filled with different propagation dielectrics, and the effects of dispersion and dielectrics on the propagation matrix and S-parameter matrix of the travelling waves are analyzed in detail. Relations of the exciting current waves in the series-connected helical Blumlein transmission lines are studied, and the dispersive transmission coefficients and reflection coefficients of electromagnetic waves at different dielectric ports are also initially analyzed. As an innovation, the proposed fully dispersive propagation theory which was demonstrated by simulation and experiments can substitute the non-propagating tape-helix dispersion theory and the non-dispersive telegraphers' equation to analyze the helical transmission lines.
An analytical method based on combination of Fourier transform and Taylor's series expansion is presented for analyzing interaction of electromagnetic cylindrical waves with inhomogeneous planar media. In the proposed method, constitutive parameters and Fourier transformed electric and magnetic fields of the inhomogeneous layer are expressed using Taylor's series expansion. Then, the unknown coefficients of the fields are obtained based on Maxwell's equations and boundary conditions. The validity of the method is verified by considering some special types of inhomogeneous media and comparing the obtained results by this method with those of other reported methods. The results show that when Fourier transform is combined with Taylor's series expansion, a powerful and quick approach is provided for solving such problems.
In this paper, we propose a new antenna structure that can be adjusted for narrow band as well as UWB applications. The proposed antenna is of very simple geometry and easy to manufacture. It is monopole type antenna and made of copper. We present antennas with the same geometrical concept and different dimensions. Antenna designed for narrow band operation exhibits 3.7% bandwidth at 800 MHz frequency (S11 < -10 dB). Two UWB antenna designs exhibit 77% bandwidth (from 2 to 4.5 GHz) and 54% bandwidth (from 2.6 to 4.5 GHz) and are of smaller size compared to the dielectric resonator antennas (DRA). Furthermore, it can be easily shown that using the proposed geometry broad family of antennas (for operation in various frequency bands) can be designed.
We present numerical time-domain modeling and validation framework for impulse-driven near-field thermoacoustics imaging. It has been recently demonstrated that this new imaging approach comprises a viable alternative for high performance and low-cost imaging using the thermoacoustic phenomenon. Placement of the imaged object in a close vicinity (near field) of an antenna elements along with generation of ultrashort (nanosecond) duration high-voltage excitation impulses further provide high imaging resolution and ensure that sufficient level of electromagnetic energy reaches the object under investigation. In order to analyze the measured results and also provide a design and optimization framework, this work presents a full-wave computational electromagnetic framework which couples the near-field electromagnetic field to the acoustic signal generation. The numerical method comprises a finite integral time domain method (FITD) based on the industry standard CST 2010 software package. The results can be further utilized for normalization and quantification of the generated images.
According to literature, a significant and up to date research direction to increase the performance level of automatic target recognition (ATR) systems is focused on the use of information coming from an appropriate set of EM sensors and high-quality decision fusion techniques, respectively. Consequently, in this paper a genetic optimized version of Sugeno's fuzzy integral is discussed. In addition, using a real database belonging to the high-resolution radar (HRR) imagery, the superiority of the proposed decision fusion technique related to its standard version and other well-known decision fusion methods is also demonstrated.
Broadband beamforming has been an important issue on antenna array processing due to many practical demands on communication, radar, or sonar applications. Although several effects deteriorating array performance have been addressed for narrowband beamforming, few of them are considered for the broadband scenario. Besides, the definition of output signal-to-interference plus noise ratio (SINR) and the way to simulate broadband signal sources are usually vague, which further obstructs the development of broadband beamforming. In this paper, the performance of discrete Fourier transform (DFT) beamformers operating in block processing and sliding window modes are investigated when the correlation matrices are known or estimated by finite data samples. The output SINR of DFT beamformers is well-defined, and the generation of broadband signals is clearly introduced. Simulation results with respect to the signal bandwidth, the number of frequency bins, and the number of data samples are presented for illustration and comparison.
There is an impetuous need for easy-to-build electrical machines with high specific thrust for various applications. The paper deals with a new modular variable reluctance tubular machine. It is a transverse flux machine without permanent magnets. Its construction is detailed and the novelty of the proposed structure is emphasized. A sample machine is analyzed by analytical and numerical means. The results of the analyses are validated by testing a laboratory model of the motor.
In this paper, a dual-fed circularly polarized antenna design with high isolation is presented for radio frequency identification(RFID) reader. The proposed antenna is excited by two fed ports connected with a circular split-ring microstrip line underneath the ground plane. A radial aperture in the ground plane provides coupling between the split-ring microstrip and radiating patch. For multiple RFID band requirements, the dimension of the aperture can be modified to obtain high isolation on different RFID Band. Finally, an antenna prototype for China RFID Band(920-925 MHz) is fabricated. The measured results agree well wit13h simulation, and show 10-dB matching bandwidth of 18%(820-1000 MHz), 3-dB axial ratio(AR) bandwidth of 11%(854-960 MHz), and 25-dB isolation bandwidth of 11 MHz(917-928 MHz).
A novel twin-diamond-shaped antenna is presented for wideband circularly polarized (CP) radiation. By introducing a twin-diamond-shaped patch and a gap-coupled feed structure, a left-handed circularly polarized (LHCP) antenna in bore-sight direction is obtained. The gap-coupled feed structure consists of a horizontal microstrip arm of approximately 0.285λ0 at the centre frequency and two small diamonds, which greatly contributes to wideband characteristics. The experimental bandwidths of 10-dB return loss and 3-dB axial ratio (AR) for the antenna prototype are about 20% and 9.2%, respectively. The measured gain is more than 6.8 dBi over the entire bandwidth.
In this work, results are given for controlling waves arbitrarily inside a new type of spatially variant lattice. To demonstrate the concept, an unguided beam was made to flow around a 90° bend without diffracting or scattering. Control of the field was achieved by spatially varying the orientation of the unit cells throughout a self-collimating photonic crystal, but in a manner that almost completely eliminated deformations to the size and shape of the unit cells. The device was all-dielectric, monolithic, and made from an ordinary dielectric with low relative permittivity (εr = 2.45). It was manufactured by fused deposition modeling, a form of 3D printing, and its performance confirmed experimentally at around 15 GHz.
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