This paper deals with the modeling of parallelepipedic magnets of various polarization directions. For this purpose, we use the coulombian model of a magnet for calculating the magnetic potential in all points in space. Then, we determine the three components of the magnetic field created by a parallepiped magnet of various polarization direction. These three components and the scalar magnetic potential are also expressed in terms of fully analytical terms. It is to be noted that the formulas determined in this paper are more general that the ones established in the literature and can be used for optimization purposes. Moreover, our study is carried out without using any simplifying assumptions. Consequently, these expressions are accurate whatever the magnet dimensions. This analytical formulation is suitable for the design of unconventional magnetic couplings, electric machines and wigglers.

In this paper, reducing Specific Absorption Rate (SAR) with ferrite sheet attachment is investigated. The finite-difference time-domain method with Lossy-Drude model is adopted in this study. The methodology of SAR reduction is addressed and then the effects of attaching location, distance, size and material properties of ferrite sheet on the SAR reduction are investigated. Computational results show that the SAR averaging over 10 gm was better than that for 1 gm and SAR reduction of 57.75% is achieved for SAR 10 gm. These results show the way to choose a ferrite sheet with the maximum SAR reducing effect for phone model.

Time modulated linear antenna arrays consisting of printed dipoles above a ground plane are simulated using the finite-difference time-domain (FDTD) method. The FDTD method brings great convenience to the investigation of the time domain responses of the time modulated arrays. In conjunction with the near-to-far field transformation in time domain, the far-field transient response can be computed to explain the physical essence of different time sequences. By employing the discrete Fourier Transform (DFT) and the frequency domain near-to-far field transformation, the radiation patterns at the frequencies of interest are obtained and are compared with the measured results. Simulation results show that the FDTD method is an effective and accurate approach for the full-wave simulation of time modulated antenna arrays.

A broadband inverted E-H shaped microstrip patch antenna is proposed and experimentally investigated. The antenna employs novel E-H shaped patch with L-probe feed technique. Prototype of the proposed antenna has been fabricated and measured for electromagnetic analysis including the impedance bandwidth, radiation pattern, and antenna gain. The designed antenna has a dimension of 80 mm by 50 mm, leading to broad bandwidths covering 1.76 GHz to 2.38 GHz. Stable radiation patterns across the operating bandwidth are observed. In addition, a parametric study is conducted to facilitate the design and optimization process.

We are developing an analytical model for the design of the folded waveguide traveling wave tube (FWTWT). This analytical model provides the physical view for rapid design optimization of the FWTWT. The design and analysis of the FWTWT using the spatial harmonics method of the TE₁₀ mode of the EM wave are presented. An X-band FWTWT is used to verify this method. The normalized dispersion and beam line equations are used to simplify the design process so that the FWTWT can be designed to operate at any desired frequency. The small signal gain of an FWTWT is calculated by using Madey's theorem. The results of this analysis are compared with the numerical single particle simulation carried out using MATLAB. The results are in excellent agreement. The Madey's theorem can be used to provide a potential indication of the gain magnitude of the FWTWT.

In this paper we propose a sparse antenna array with nine elements for the integrated system of communication and direction finding. The main idea is that the sparse antenna array, whose element spacing is relatively larger than half wavelength, are divided into six two-element subarrays to transmit multi-beam. According to the spatial correlation characteristics of multi-beam, a packet exciting method employing multi-carrier Orthogonal Frequency Division Multiplexing (OFDM) signal is designed to modulate the directional information into the signal space of subcarriers. In this way, a receiver with a single antenna can accomplish communication and direction-finding function by demodulation received signal. For the direction finding algorithm of the sparse antenna array, an approximate algorithm is designed to resolve the ambiguity problem based on the Chinese remainder theorem. Simulation results show that the proposed sparse antenna array can be applied to the integrated application of communication and direction finding.

The di®raction of a plane electromagnetic wave by an ideal metallic sphere (Mie's theory) is investigated by a new method. The method represents the charge disturbances (polarization) by a displacement field in the positions of the mobile charges (electrons) and uses the equation of motion for the polarization together with the electromagnetic potentials. We employ a special set of orthogonal functions, which are combinations of spherical Bessel functions and vector spherical harmonics. This way, we obtain coupled integral equations for the displacement field, which we solve. In the non-retarded limit (Coulomb interaction) we get the branch of "spherical" (surface) plasmons at frequencies ω = ω_psqrt(l/(2(l/ + 1)), where ω_p is the (bulk) plasma frequency and l = 1, 2,.... When retardation is included, for an incident plane wave, we compute the field inside and outside the sphere (the scattered field), the corresponding energy stored by these fields, Poynting vector and scattering cross-section. The results agree with the so-called theory of "effective medium permittivity", although we do not start the calculations with the dielectric function. In turn, we recover in our results the well-known dielectric function of metals. We have checked the continuity of the tangential components of the electric field and continuity of the normal component of the electric displacement at the sphere surface, as well as the conservation of the energy flow and re-derived the "optical theorem". In the limit of small radii (in comparison with the electromagnetic wavelength) the sphere exhibits a series of resonant absorptions at frequencies close to the plasmon frequencies given above. For large radii these resonances disappear.

We propose an optimization methodology suitable for the design of various antenna structures. This methodology includes a rapidly-converging iterative scheme. In each iteration stage, the algorithm generates a parameterized Cauchy model using the available results from previous iterations. Optimization is then applied to this Cauchy model to obtain better design parameters that are also used in enhancing the accuracy of the model. This cycle continues until the specifications are met. In addition, this on-the-fly technique produces an analytical model of the behavior of the antenna structure. Sensitivity and tolerance analyses can thus be efficiently carried out without the need for further costly electromagnetic simulations.

This paper deals with the potential of ultra-wideband (UWB) microwave imaging for the detection and localization of breast cancer in its early stages. A method is proposed for locating tumors which is based on the signal time-of-flight backscattered by the tumor. Time-of-flight is detected using a wavelet transform algorithm. The feasibility of the method has been investigated by means of simulated results using Finite-Difference Time-Domain (FDTD) and experimental results with a UWB radar and a phantom.

A series of curved microstrip antennae with defected ground structure for multiband are proposed，which are more smaller, conveniently conformal, wider radiation beam and suitable for WLAN terminal for different environment. The relation between the main geometry parameters and the antennas' characters are studied with the cavity model method and EM simulation, and the optimum size antenna is achieved later. If keeping the other parameters but increasing the curving angle α, the return loss is almost good at f=2.45 GHz, but poor at f=5.25 GHz and 5.8 GHz. After slight tuning the key parameters, these curved antennae all can work at f=2.45 GHz, 5.25 GHz and 5.8 GHz, and their patterns in the plane that is vertical to the curve axes become more wider or even omni-directional with the curving angle α increasing, which are verified by experiment, their measured gain are 2 dB--6.3 dB.

The Linear Frequency Modulation (LFM) waveform is the most commonly and extensively used signal in practical radar system. However a compressed LFM signal at the receiver will produce the first sidelobe at a level of -13 dB to the peak of the main lobe. A weighting function is needed to apply in order to reduce the sidelobes. However, the penalty of mismatch loss is clearly evident. It may reduce output SNR, typically by 1 to 2 dB. Every single dB of additional SNR can have great effects in reducing false alarm rates in target detection applications. In an effort to achieve low autocorrelation sidelobe level without applying weighting function, Non-Linear Frequency Modulation (NLFM) signal has been investigated. This paper describes the sidelobe reduction techniques using simple two-stage FM waveform, modified two-stage FM waveform and tri-stage FM waveform. Simulation results of the proposed NLFM signal are presented. Sidelobe reduction of more than -19 dB can be achieved by this design without any weighting technique applied.

The edge-based finite element method is used for the solution of scattering problems. The factorized sparse inverse preconditioner is considered for the conjugate gradient iterative solution of the large sparse linear systems generated from the finite element method. The efficiency of the proposed preconditioner is illustrated on a set of model problems in the final of the paper. The results suggest that the sparse inverse preconditioner is very efficient for the solution of large-scale electromagnetic scattering problems.

A simple half oval patch antenna is proposed for the active breast cancer imaging over a wide bandwidth. The antenna consists of a half oval and a trapezium, with a total length 15.1 mm and is fed by a coaxial cable. The antenna performance is simulated and measured as immersed in a dielectric matching medium. Measurement and simulation results show that it can obtain a return loss less than -10 dB from 2.7 to 5 GHz. The scattered field detection capability is also studied by simulations of two opposite placed antennas and a full antenna array on a cubic chamber.

In this paper, a wideband planar dipole antenna is proposed. Compared to conventional dipole antennas, this antenna has wideband impedance matching, simple structure and compact size. From EM simulations, dimensions of antennas are chosen for better performance. For verification, this newly proposed structure is fabricated and measured. It is shown that return loss of the antenna between 2.5 GHz and 8.0 GHz is better than -10 dB.

This paper presents the analysis and design of a two-probe excited circular ring antenna. The analysis is conducted by using induced emf method and transmission line model. The design process is to choose a suitable radius of the ring for a single probe antenna. Then, the suitable probe length and ring length are determined for the two-probe antenna. Finally, isolation between the two probes is enhanced by insertion of an inductor coil between the probes. The operational characteristics of the prototype antenna at the frequency of 5.2 GHz are measured and compared with calculation results. It is evident that these results are in good agreement. The antenna achieved isolation in excess of 20 dB and VSWR less than 2:1 over the desired bandwidth and a bidirectional radiation pattern with 4 dBi gain. This antenna is suitable for Multiple-Input Multiple-Output (MIMO) system covering a long and narrow environment.

We studied the practical limitations of a linearly transformed invisibility cloak due to the loss and discretization. We found that in order for the cloaking applications to be practically useful, for example, to reduce the scattering by two orders, the maximum loss tangent allowed in the cloak needs to be of or within the order of 0.01, which also limits the radius of a concealed object to be roughly within one wavelength. For a large cloak, if its size is increased by one order, the maximum allowed loss tangent needs to be reduced by one order accordingly. For discretization, we studied both lossless and lossy cases and found that a little loss will expedite the convergence of scattering with increase of the number of layers. Insufficient layers may increase the scattering and thus make the object more visible instead of invisible.

In this paper, a novel electromagnetic bandgap structure (EBGs) is proposed, which is similar to the mushroom-like EBG. By introducing double reverse split rings (RSR) into the square patch, the size of EBG cell is reduced by 30%, and the bandgap achieves bandwidth about 65%. A fractal microstrip antenna is implemented using the EBGs as a ground plane, and the measured results show that the reduction in the surface wave level is remarkable. Compared with the reference antenna at 5 GHz, an approximately 8 dB improvement of the return loss is achieved, and the back lobe is reduced by 10 dB in E plane and 8.73 dB in H plane at the resonant frequency, respectively. The front-back ratios of the antenna have significantly increased from 4.9 GHz to 5.2 GHz.

In this paper, a novel technique for electronic beam steering in time modulated linear array (TMLA) is proposed. The beam steering technique is realized at the first sideband by controlling the switch-on time sequences of each element in the TMLA without using phase shifters. The differential evolution (DE) algorithm is employed to improve the gain and suppress the sidelobe levels (SLLs) at both the center frequency and the first sideband, simultaneously. An S-band 8-element double-layered printed dipole linear array was used to verify the technique experimentally. Measured results are compared with numerical data, and good agreement is reported. Moreover, some simulation results on the binary phase shift keying (BPSK) modulated signals arriving from different directions received by the proposed approach are presented, which validates the application of the proposed beam steering technique.

Tracking a target is a fundamental and crucial problem in wireless sensor networks. It is well known that non-line-of-sight (NLOS) propagation will significantly degrade the tracking accuracy if its effects are ignored. In this paper, a line-of-sight (LOS) identification approach for range-based tracking systems is developed to discard the NLOS measurements. Based on Lp-norm LOS identification strategy, a novel target tracking method is devised with the use of cost-reference particle filter, which does not require the knowledge of the measurement noise distribution. Computer simulations are included to verify the effectiveness of the proposed approach under different noise distributions.

The capacitance of the circular parallel plate capacitor is calculated by expanding the solution to the Love integral equation into a Fourier cosine series. Previously, this kind of expansion has been carried out numerically, resulting in accuracy problems at small plate separations. We show that this bottleneck can be alleviated, by calculating all expansion integrals analytically in terms of the Sine and Cosine integrals. Hence, we can, in the approximation of the kernel, use considerably larger matrices, resulting in improved numerical accuracy for the capacitance. In order to improve the accuracy at the smallest separations, we develop a heuristic extrapolation scheme that takes into account the convergence properties of the algorithm. Our results are compared with other numerical results from the literature and with the Kirchhoff result. Error estimates are presented, from which we conclude that our results is a substantial improvement compared with earlier numerical results.