In this paper, the finite-difference frequency-domain (FDFD) method, boundary integral equation (BIE) method and sub-entire-domain (SED) basis functions are combined to analyze scatterings from finite periodic dielectric gratings. The wavelet method is used to reduce the number of inner product operations in calculating the mutual-impedance elements between the SED basis functions. In the numerical examples, the RCS curves obtained by the method in this paper are in good agreement with those obtained by the classical full-domain FDFD method, but the computational times are largely reduced and no large matrix equation needs to be stored and solved in the former.

In this paper, we consider a novel class of Krylov projection methods computed from the Lanczos biconjugate A-Orthonormalization procedure for the solution of dense complex non-Hermitian linear systems arising from the Method of Moments discretization of Maxwell's equations. We report on experiments on a set of model problems representative of realistic radar-cross section calculations to show their competitiveness with other popular Krylov solvers, especially when memory is a concern. The results presented in this study will contribute to assess the potential of iterative Krylov methods for solving electromagnetic scattering problems from large structures enriching the database of this technology.

The effect of magnetic bias on dielectric spectra of composite sheets filled with Fe or Co-based microwires is studied experimentally and via simulation. The permittivity is measured using a free-space technique within the frequency band from 6 to 12 GHz. The bias is applied either parallel or perpendicular to the microwave electric field; the bias strength varies from 0 to 2.5 kOe. The composites with Fe-based wires reveal a single region of bias dependent permittivity under bias about 800-1000 Oe. The composites with Co-based wires reveal two such regions: the high-field region is close to that of composites with Fe wires, and the low-field region corresponds to the coercive field of Co wires (2-3 Oe). The high-field effect is related to the dependence of ferromagnetic resonance (FMR) parameters on bias; the low-field effect is related to the rearrangement of the domain structure of Co-based wires. The interference of magnetoimpedance and dipole resonance is analyzed, revealing the effects off wire length, diameter, parameters of magnetic resonance and composite structure. The results are considered in view of application to the problem of controlled microwave attenuation. Simulation shows that the narrower is the FMR spectrum and the higher is the admissible loss of a sheet in a transparent state, the wider is the dynamic range of attenuation control. The attenuation range of a lattice of continuous wires is smaller than that of a screen with identical wire sections, where the magnetoimpedance effect is amplified resonantly. At 15 GHz frequency the strength of the bias switching opaque sheet with Fe-based wires to the transparent state is about 2000 Oe. For 3 dB admissible loss, the range of attenuation control about 10 dB is feasible in a composite with aligned wire sections. If the aligned sections are distributed regularly, the loss in a transparent state is about 1 dB lower.

We propose some fascinating results regarding dark soliton pulse propagation within the nonlinear micro and nano waveguides. The system consists of nonlinear micro and nanoring resonators whereby the dark soliton is input into the system and travels within the waveguide. A continuous dark soliton pulse is sliced into smaller pulses by the nonlinear effect which is known as chaos. The nonlinear behaviors such as chaos, bistability and bifurcation are analyzed and discussed. The broad area of applications such as dark-bright soliton conversion and power amplification, binary code generation by the dark-bright soliton pair, dark soliton trapping and millimeter wave generation are proposed and discussed. The biggest advantage is that, where security is the most important consideration, power amplification can be used to perform the long distance link.

The interplay effects of matrix formulations with microwave on drug release were investigated using an agglomerate system. Chitosan spheroids were formulated with stearic acid and/or sodium chloride by extrusion-spheronization technique, and chlorpheniramine maleate as water-soluble model drug. The spheroids were treated by microwave at 80 W for 5 to 40 min. The profiles of drug dissolution, drug content, drug-polymer interaction, polymer-polymer interaction, sodium leaching, matrix morphology and integrity were determined. Unlike chitosan matrix prepared by ionotropic gelation method, the retardation of drug release from chitosan spheroids by microwave required a more complex formulation containing both stearic acid and sodium chloride unless a high stearic acid fraction was used. These spheroids demonstrated a high resistance to disintegration during dissolution owing to salt-induced bridging by sodium chloride. In response to microwave, sodium chloride aided stearic acid spread and effected domain interaction via C=O moiety over a matrix with reduced specific surface area thereby reducing drug dissolution. The drug release of spheroids can be retarded by microwave through promoting the layering of hydrophobic stearic acid in a matrix structure sustained by sodium chloride.

Specific rain attenuation is discussed from the viewpoint of numerical solution for scattering and absorption of electromagnetic waves related to dielectric spheres. Special attention is paid to the quantitative evaluations considering the change of temperature and the existence of multiple scattering effect. The analysis is based on the set of Stratton's vector spherical wave functions and its addition theorem, which lead to the simultaneous linear equations for the expansion coefficients with adaptively selected truncation numbers. Computed extinction cross sections lead directly to the specific rain attenuation, where the Weibull raindrop distribution model is used. It is discussed how the dependence of the permittivity of water on temperature and frequency affects the attenuation property. Furthermore, the effect of multiple scattering is evaluated in terms of the root mean square of attenuation deviation from the simple superposition of single scattering (Mie's) coefficients. Contrary to general belief, this deviation is the highest at around the boundary between microwave and millimeter wave bands.

A theoretical study and a simulation method are proposed for superparamagnetic current sensors implementing a uniformly wound toroidal core topology. So as to be easy to implement, this sensor topology can be made flexible thanks to the use of a core made up of a superparamagnetic powder embedded in a flexible plastic matrix. The measurement of DC and AC currents is possible provided that a sinusoidal magnetic field excitation is applied to the superparamagnetic transducer. An analytical model is proposed for computing the sensor output signal and we demonstrate that when the detection of the component at the second order harmonic of the excitation frequency is used, the measurement is independent of the conductor position in a given current range. For simulating the dynamic response of the sensor, we propose to combine the analytical model, or a finite elements model, with a time-discretization method. Furthermore, simulations are carried out considering a ring shaped sensor and the real magnetization characteristics of a superparamagnetic material. Simulations are provided over the [-10 kA 10 kA] range and for various amplitudes of the excitation signal. The results obtained with the analytical model, which is computationally efficient, are within 4% to 12.7% from the numerical results.

The observed phenomena in actual electromagnetic environment are inevitably contaminated by the background noise of arbitrary distribution type. Therefore, in order to evaluate the electromagnetic environment, it is necessary to establish some signal processing methods to remove the undesirable effects of the background noise. In this paper, we propose a noise cancellation method for estimating a specific signal with the existence of background noise of non-Gaussian distribution. By applying the well-known least mean squared method for the moment statistics with several orders, a practical method for estimating the specific signal is derived. The effectiveness of the proposed theoretical method is experimentally confirmed by applying it to an estimation problem in actual magnetic field environment.

In this paper, the coupled mode theory is used to analyze apodized fiber Bragg gratings (FBGs). Since the profile of gratings varies with the propagation distance, the coupled mode equations (CMEs) of apodized FBGs are solved by the fourth-order Runge-Kutta method (RKM) and piecewise-uniform approach (PUA). We present two discretization techniques of PUA to analyze the apodization profile of gratings. A uniform profile FBG can be expressed as a system of first-order ordinary differential equations with constant coefficients. The eigenvalue and eigenvector technique as well as the transfer matrix method is applied to analyze apodized FBGs by using PUAs. The transmission and reflection efficiencies calculated by two PUAs are compared with those computed by RKM. The results show that the order of the local truncation error of RKM is h^-4, while both PUAs have the same order of the local truncation error of h^-2. We find that RKM, capable of providing fast-convergent and accurate numerical results, is a preferred method in solving apodized FBG problems.

The Goos-Hanchen (GH) shift of the reflected waves from nonlinear nanocomposites of interleaved nonspherical metal and dielectric particles are investigated both theoretically and numerically. First, based on spectral representation theory and effective medium approximation, we derive the field-dependent effective permittivity of the nonlinear composites. Then the stationary phase method is adopted to study the GH shifts from nonlinear composites. It is found that for a given volume fraction, there exist two critical polarization factors L_c1 and L_c2, and bistable GH shifts appear only when L < L_c1 or L < L_c2. Moreover, both giant negative and positive GH shifts accompanied with large reflectivity are found, hence they can be easily observed in experiments. The reversal of the GH shift may be controlled by adjusting both the incident angle and the applied field. Numerical simulations for Gaussian-type incident beam are performed, and good agreement between simulated data and theoretical ones is found especially for large waist width.

This paper describes an augmented generalized impedance boundary condition (AGIBC) formulation for accurate and efficient modeling of conductive media. It is a surface integral equation method, so that it uses a smaller number of unknowns. The underlying GIBC provides a rigorous way to account for the skin effect. Combining with the novel augmentation technique, the AGIBC formulation works stably in the low-frequency regime. No looptree search is required. The formulation also allows for its easy incorporation of fast algorithms to enable the solving of large problems with many unknowns. Numerical examples are presented to validate the formulation.

In this paper, the solution of two-dimensional inverse scattering problems is addressed by probing the unknown scenarios with TE and TM waves. To better exploit the information content of the scattered data the multi-zooming approach is used. The results of experiments with single as well as multiple scatterers are reported and discussed also in comparison with single-polarization inversions.

In this paper, several kinds of photonic crystal fibers (PCFs) have been proposed and characterized. Two types of PCF structures have been proposed, air holes in silica or silica rods in air in a triangular lattice around the core. It has been shown that by reshaping the cladding holes, varying the diameters of the holes in one or two rows around the core or changing the refractive index of the holes, different types of specialty fibers, such as dispersion shifted fibers (DSFs), non-zero dispersion shifted fibers (NZ-DSFs), dispersion flattened fibers (DFFs), dispersion compensating fibers (DCFs), and polarization maintaining fibers (PMFs), can be designed. The PCF core is silica to support the propagation of lightwave by total internal reflection (TIR) in the third telecommunication window. The chromatic dispersion, confinement loss and modal birefringence of the proposed specialty fibers have been numerically derived.

In conventional statistical STAP algorithms, the existence of interference target in training samples will lead to signal cancellation, resulting in the output SCR falling and the moving target detection performance degrading. The nonhomogeneity detector is an effective way to restrain the outlier, which can improve the covariance matrix estimation by detecting the samples containing outliers and rejecting them, and improve the STAP performance. A new interference target detection algorithm is proposed in this paper, the outlier detection is realized by using the samples' data phase information. Compared with traditional method, the improved algorithm is more sensitive to interfering target with different azimuth and intensity. Simulation results demonstrate the validity of this improved method.

Designing antennas in the presence of electrically large and complex structures such as cars or aircrafts has become an important issue for next generation communication systems. Based on the principle of equivalence, the hybridization approach integrating FIT-UTD techniques has shown its superiority in terms of its computing efficiency. In such approach, discrete samplings of continuous electric or magnetic field components resulted from low frequency (LF) sub-domain are required to be converted to the excitation current sources for the high frequency (HF) sub-domain. Thus, the overall accuracy of the calculation results will strongly depend on the similarities between the sampled and original field distributions with both the magnitude and phase involved. In this paper, convergence study of electric and magnetic current sampling is performed. Impact of the different sampling profiles on the overall accuracy is also investigated through numerical examples. Results reveal that convergence of the far-field radiation patterns are closely related to the sampling profiles.

In this work, ideally hard struts with different cross sections are analyzed. Firstly, the characterization of the invisibility of a given object in terms of an equivalent blockage width is discussed. Then, the effect of the incidence angle on struts for reducing electromagnetic blockage using the same ideally hard cylinders is analyzed. It is shown that the variation of incidence angle in azimuth is very sensitive in terms of blockage for both polarizations. Finally, design charts for ideally hard struts which reduce blockage simultaneously for TE and TM cases are presented. This can be used to define some performance goals for final realized struts.

The novel characteristics of power propagation of guided modes in the chiral nihility fiber have been investigated theoretically. The formulas of electromagnetic fields in the core and cladding for guided modes are presented in detail. The dispersion equations, energy flux and power of guided modes are derived. The numerical results are given and discussed. Some exotic features of power propagation have been found in the chiral nihility fiber.

In this paper, rainfall effect on the VHF radio-wave propagation in a tropical forest is further studied in details. Theoretical study and experimental investigations are performed with the help of a four-layered model for forested environment. It is found that the lateral wave traveling along the air-canopy interface, the direct waves, and the ground reflected waves are the main modes for VHF radio-wave propagation in forest. The rainfall can affect these propagating waves to different extents. Especially, due to the increase in the dielectric permittivity of the wet canopy layer by rain water, the time of arrival of the direct wave traveling through the canopy layer can be delayed significantly. Finally, the dielectric permittivity for the wet canopy layer under different rain events is evaluated empirically.

An analytical model of an effective permittivity of a composite taking into account statistically distributed orientations of inclusions in the form of prolate spheroids will be presented. In particular, this paper considers the normal Gaussian distribution for either zenith angle, or azimuth angle, or for both angles describing the orientation of inclusions. The model is an extension of the Maxwell Garnett (MG) mixing rule for multiphase mixtures. The resulting complex permittivity is a tensor in the general case. The formulation presented shows that the parameters of the distribution law for orientation of inclusions affect the frequency characteristics of the composites, and that it is possible to engineer the desirable frequency characteristics, if the distribution law is controlled.

In this paper, three approaches for the synthesis of the optimal compromise between sum and difference patterns for sub-arrayed linear and planar arrays are presented. The synthesis problem is formulated as the definition of the sub-array configuration and the corresponding sub-array weights to minimize the maximum level of the sidelobes of the compromise difference pattern. In the first approach, the definition of the unknowns is carried out simultaneously according to a global optimization schema. Differently, the other two approaches are based on a hybrid optimization procedures, exploiting the convexity of the problem with respect to the sub-array weights. In the numerical validation, representative results are shown to assess the effectiveness of the proposed approaches. Comparisons with previously published results are reported and discussed, as well.

This paper presents an Extended Exact Transfer Function (EETF) algorithm for Bistatic Synthetic Aperture Radar (BiSAR) imaging of a Translational Invariant (TI) case. This algorithm adopts directly the 2D transfer function of monostatic SAR (MoSAR), instead of deriving a new one, by converting the BiSAR into an equivalent MoSAR. A new azimuth phase compensation function is constructed through exploiting this equivalency. Geometry distortion correction for BiSAR imaging result is considered in the proposed algorithm. In addition, the applying condition of the algorithm is also discussed. One desirable property of the proposed algorithm is that the computing flow and efficiency are the same as ETF algorithm for MoSAR. The effectiveness is validated by point target simulations with Tandem and forward-looking configuration.

This paper discusses the design and development of a FPGA-based chirp generator for high resolution Unmanned Aerial Vehicle (UAV) Synthetic Aperture Radar. The desired bandwidth of the chirp signal is 100 MHz (combination of I and Q channels) with a chirp rate of 5 MHz/μs. Two algorithms based on the Memory-based architecture and the Direct Digital Synthesizer (DDS) architecture are presented. The measurement results indicate that the DDS chirp generator is a preferred choice for high-resolution SAR application.

Biological effects due to whole-body radio-frequency exposure may be induced by core temperature elevation. According to the international safety guidelines/standards for human protection, the whole-body averaged specific absorption rate (WBA-SAR) is used as a metric. In order to understand the relationship between WBA-SAR and core temperature elevation, a theoretical solution or a closed formula for estimating core temperature elevation is essential. In the present study, we derived a formula for simply estimating core temperature elevation in humans and animals due to whole-body radio-frequency exposure. The core temperature elevation estimated with the formula is found to be in reasonable agreement with the computational results of finite-difference time-domain computation incorporated in anatomically-based models. Based on the formula, the WBA-SAR is found to be a good metric for estimating core temperature elevation. The main factors influencing the core temperature elevation are the perspiration rate and the body surface area-to-weight ratio.

A study of electromagnetic wave propagation in dense plasmas when the wave frequency is below the cut-off frequency is presented. A three-layer symmetric structure consisting of dense plasma nested between two boundary layers is studied analytically and numerically. The permittivity of the dense plasma is negative, while the permittivity of each boundary layer is greater than 1. It is shown that total transmission of an electromagnetic wave can be achieved if an adequate incidence angle, dielectric permittivity of the boundary layers and corresponding boundary layer widths are chosen. It is found that plasma transparency is due to resonance between the evanescent waves in the dense plasma region and the standing waves in the boundary layers. Resonance conditions are derived analytically and the relationship between the corresponding parameters of the problem are studied numerically.

In this paper, electromagnetic scattering of a plane wave by large inhomogeneous arbitrarily shaped bi-anisotropic objects is solved by Adaptive Integral Method (AIM). Based on Maxwell equations and constitutive relationship for general bi-anisotropic media and using Volume Integral Equations (VIE), the electromagnetic fields are derived as functions of equivalent volume sources. Then the integral equations are discretized using Method of Moments (MoM). Because of the dense matrix property, MoM cannot be used to solve electromagnetic scattering by large objects. Therefore, AIM is adopted to reduce the memory requirement and speed up the solution process. Comparison between AIM and MoM with respect to CPU time and memory requirement is done to show the efficiency of AIM in solving electromagnetic scattering by large objects. Numerical results are obtained for some canonical cases and compared with Mie theory, in which excellent agreement is observed. some new numerical results are also presented for the more general bi-anisotropic material media.

Ultra Wideband (UWB) radar is a promising emerging technology for breast cancer detection based on the dielectric contrast between normal and tumour tissues at microwave frequencies. One of the most important considerations in developing a UWB imaging system is the configuration of the antenna array. Two specfic configurations are currently under investigation, planar and cylindrical. The planar configuration involves placing a conformal array of antennas on the naturally attened breast with the patient lying in the supine position. Conversely, the circular configuration involves the patient lying in the prone position, with the breast surrounded by a circular array of antennas. In order to effectively test the two antenna configurations, two 2D Finite-Difference Time-Domain (FDTD) models of the breast are created, and are used to simulate backscattered signals generated when the breast is illuminated by UWB pulses. The backscattered signals recorded from each antenna configuration are passed through a UWB beamformer and images of the backscattered energy are created. The performance of each imaging approach is evaluated by both quantitative methods and visual inspection, for a number of test conditions. System performance as a function of number of antennas, variation in tissue properties, and tumour location are examined.

The Radio Frequency Identification (RFID) applications are growing rapidly, especially in the UHF frequency band that is being used in inventory management. Passive UHF tags are preferred for these applications. In this paper, RFID reader-to-reader interference is analyzed. A model to estimate the minimum distance between readers to achieve a desired probability of detection in real multipath environments is derived and compared to the ideal case (AWGN channel). Diversity techniques to combat multipath and interference effects are proposed and studied.

Flat left-handed metamaterial (LHM) lens can generate appropriate focusing spot in biological tissue as required in microwave tumor hyperthermia treatment. By using single flat LHM lens to concentrate microwave in a mass of tissue covered by water bolus, microwave hyperthermia scheme is proposed for superficial tumor hyperthermia. The power distribution in tissue is simulated by finite-difference time-domain method, and the thermal pattern is calculated by solving the bio-heat transfer equation. It is demonstrated that, by using a flat LHM lens of thickness of 4 cm to concentrate microwave of 2.45 GHz, a temperature above 42^oC can be achieved and maintained in one hour in a tissue region of about 1.0 cm in width and 1.2 cm in depth in tissue with the source amplitude of 43.40 V/cm, which is suitable for superficial tumor hyperthermia. By adjusting the position of microwave source, the heating zone in tissue can be adjusted in both the lateral and depth direction in tissue. The effects of fat layer and water bolus on the performance of hyperthermia are investigated as well.

This paper deals with the experimental validation of an effective near-field-far-field transformation technique with helicoidal scanning particularly suitable for electrically long antennas, whose validity has been numerically assessed in a previous authors' paper. Such a technique relies on the results relevant to the nonredundant sampling representations of the electromagnetic fields and makes use of an optimal sampling interpolation algorithm, which allows the reconstruction of the near-field data needed by the near-field-far-field transformation with cylindrical scan. The use of a prolate ellipsoid instead of a sphere to model an elongated antenna allows one to consider measurement cylinders with a diameter smaller than the antenna height, thus reducing the error related to the truncation of the scanning zone. Moreover, a significant reduction of the needed near-field data is also obtained. The comparison of the far-field patterns reconstructed from the acquired helicoidal measurements with those obtained from the data directly measured on the classical cylindrical grid assesses the effectiveness of the near-field-far-field transformation using this innovative scanning technique. At last, its validity is further confirmed by the very good agreement with the direct far-field measurements.

A numerical method is developed to calculate/simulate the separation of non-metallic inclusions from an aluminum melt by using a strong magnetic field (e.g., 10 Tesla) with high gradient generated via a superconducting magnet. The cases with and without imposed DC current on liquid aluminum in a cylindrical channel are discussed and compared. The migrating velocities of the non-metallic inclusions in an aluminum melt are calculated through force analysis and Navier-Stokes equations. In addition, the trajectories and removal efficiencies of the inclusions are evaluated. It is found that particle trajectories are influenced by the imposed flow rate and inclusion particle size. In addition, the removal efficiency is improved significantly, especially for small inclusions, e.g., <10 μm, by an imposed DC current on liquid aluminum in the high gradient area of a magnetic field.

Although classical imaging is limited by the Rayleigh criterion, it has been demonstrated that subwavelength imaging of two point-like scatterers can be achieved with probing sensors arrays, even if the scatterers are located in the far field of the sensors. However, the role of noise is crucial to determine the resolution limit. This paper proposes a quantitative study of the influence of noise on the subwavelength resolution obtained with the DORT-MUSIC method. The DORT method, French acronym for decomposition of the time reversal operator, consists in studying the invariants of the time reversal operator. The method is combined here with the estimator MUSIC (MUltiple SIgnal Classification) to detect and image two close metallic wires. The microwaves measurements are performed between 2.6 GHz and 4 GHz. Two wires of λ/100 diameters separated by λ/6 are imaged and separated experimentally. To interpret this result in terms of noise level, the analytical expression of the eigenvectors of the time reversal operator perturbed by the noise is established. We then deduce the noise level above which the subwavelength resolution fails. Numerical simulations and experimental results validate the theoretical developments.

In this paper, one of the subspace signal processing methods, namely time reversal multiple signal classification (TR-MUSIC), is firstly employed for electromagnetic subsurface detection where the multilayered dyadic Green's function is used. Therewith, one obtains the improved location and superresolution imaging for underground detecting application. The imaging pseudo-spectrum is accordingly defined for both the echo-mode and transmit-mode TR-MUSIC methods, by analyzing the obtained multistatic response matrix. Based on the theoretical formula, we carry out the numerical simulation using the half-space dyadic Green's function in noisy scenario. The results show that the MUSIC imaging algorithm achieves the enhanced resolution and the transmit-mode method gives more robust output when performance comparison of the four methods is made, therefore indicate the TR-MUSIC could be a good candidate for subsurface detection.

Using ultra-wide band (UWB) microwave pulse for breast cancer detection has been greatly investigated recently since it does not impose the patient to any harmful radiation and the implementation is relatively cheaper than other methods such as MRI or X-ray. An issue in UWB imaging of breast cancer is the strong backscatter from the breast skin which is in orders of magnitude larger than the pulse backscattered from the tumor and should be eliminated before processing the signal for the tumor detection and imaging. At present no existing method can effectively remove this artifact without introducing corruption to the tumor signature. In this paper, a novel method to eliminate this artifact is proposed which employs a frequency domain model to isolate and remove skin related information from the signal. This method is compared with the existing methods of the skin artifact removal in different scenarios. The results show that the new method can overcome the shortcomings of the previous methods and improve the detection of the tumor in the sense of the tumor to clutter response ratio.

In this work, a far field imaging model based on the array structure of positive- and negative-refractive-index media and modulation subwavelength-gratings is firstly presented and is named as the multilayer far field superlens (MLFSL). This new lens is capable of producing optical images by enhancing evanescent waves to the far field. The principle of MLFSL is discussed in detail, and the necessary and sufficient condition for designing MLFSL is obtained. Simultaneously, off-axis illumination technology is introduced to MLFSL system to further improve super-resolution, and the transfer matrix which contains the incidence angles is obtained. The results demonstrate that, compared with other far field superlens, the subwavelength resolution of MLFSL has been enhanced. Such remarkable imaging capability of MLFSL promises new potential for nanoscale imaging and lithography.

Electromagnetic field will scatter when incident on boundaries separating media with different constitutive parameters. This paper demonstrates the use of a differential operator on recorded scattered waves to reveal the shape of the boundary. The method is noninvasive and is composed of three phases. First, the area of interest is illuminated and the resulting scattered electromagnetic fields are recorded. In the 2nd phase, the captured data is numerically reverse simulated in time to reconstruct the field distribution in the region of interest. Finally, the differential imaging operator is applied on the reconstructed wave field, creating an image delineating the boundary where scattered fields originated. This technique does not require the knowledge of location of the boundaries nor the nature of the discontinuity in the constitutive parameters. The proposed imaging system is scalable, whereby modification of the source signal, recorder sampling, and numerical model allows imaging objects of smaller dimensions and creation of sharper and more accurate images.

On the basis of analyzing the principle of multicarrier DS-CDMA, we propose a novel multiband complex wavelet based multicarrier DS-CDMA system in this paper by using the optimized multiband complex wavelet as multicarrier basis function. The system bit error rate (BER) performance is investigated over Nakagami-m Rayleigh fading channel. Without any cyclic prefix (CP), the proposed system can avoid the decrease of spectrum efficiency and data rate of conventional multicarrier DS-CDMA with CP. Meanwhile, the space diversity combining (SDC) technique based on multi-antenna receiver is employed to improve the system performance further. By the mathematical derivation, the BER analysis of the system with or without SDC is given in detail. Theoretical analysis and simulation results show that the proposed multicarrier system outperforms the conventional multicarrier DS-CDMA system and real wavelet packet based multicarrier DS-CDMA system due to the superior properties of the optimized multiband complex wavelet. Especially, the application of SDC technique can effectively improve the system ability against spatial fading and interferences, and thus the superior performance is obtained.

Gaussian process (GP) regression is proposed as a structured supervised learning alternative to neural networks for the modeling of CPW-fed slot antenna input characteristics. A Gaussian process is a stochastic process and entails the generalization of the Gaussian probability distribution to functions. Standard GP regression is applied to modeling S₁₁ against frequency of a CPW-fed secondresonant slot dipole, while an approximate method for large datasets is applied to an ultrawideband (UWB) slot with U-shaped tuning stub --- a challenging problem given the highly non-linear underlying function that maps tunable geometry variables and frequency to S₁₁/input impedance. Predictions using large test data sets yielded results of an accuracy comparable to the target moment-method-based full-wave simulations, with normalized root mean squared errors of 0.50% for the slot dipole, and below 1.8% for the UWB antenna. The GP methodology has various inherent benefits, including the need to learn only a handful of (hyper) parameters, and training errors that are effectively zero for noise-free observations. GP regression would be eminently suitable for integration in antenna design algorithms as a fast substitute for computationally intensive full-wave analyses.

A low profile double-layer polarizer structure is presented for planar patch antennas to obtain circular polarization in 3.5 GHz WiMAX band (3.4-3.6 GHz≈5.7% bandwidth). Each polarizer layer is composed of 45º tilted metallic strips on a printed circuit. A bandwidth widening is obtained due to a significant reduction of the distance between polarizer and patches. The associated effects from the interaction of the two structures have been studied. A 2x2 array prototype has been implemented and measured, with a 8% average bandwidth in reflection and dual linear/circular polarization.

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.

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.