Showing papers in "Progress in Electromagnetics Research-pier in 2015"
TL;DR: In this paper, the basic theory for treating the propagation of optical beams in turbulent atmosphere is described, and recent theoretical and experimental developments on propagation of a partially coherent beam in turbulent environment are reviewed.
Abstract: Partially coherent beam is preferred in many applications, such as free-space optical communications, remote sensing, active laser radar systems, etc., due to its resistance to the deleterious effects of atmospheric turbulence. In this paper, after presenting a historical overview on propagation of optical beams in turbulent atmosphere, we describe the basic theory for treating the propagation of optical beams in turbulent atmosphere and we mainly introduce recent theoretical and experimental developments on propagation of partially coherent beam in turbulent atmosphere. Recent progress on the interaction of a partially coherent beam with a semirough target in turbulent atmosphere and the corresponding inverse problem are also reviewed.
128 citations
TL;DR: The proposed THE AUTHORS + HBP-FNN method achieves nearly perfect detection pathological brains in MRI scanning.
Abstract: Background) We proposed a novel computer-aided diagnosis (CAD) system based on the hybridization of biogeography-based optimization (BBO) and particle swarm optimization (PSO), with the goal of detecting pathological brains in MRI scanning. (Method) The proposed method used wavelet entropy (WE) to extract features from MR brain images, followed by feed-forward neural network (FNN) with training method of a Hybridization of BBO and PSO (HBP), which combined the exploration ability of BBO and exploitation ability of PSO. (Results) The 10 repetition of k-fold cross validation result showed that the proposed HBP outperformed existing FNN training methods and that the proposed WE + HBP-FNN outperformed fourteen state-of-the-art CAD systems of MR brain classification in terms of classification accuracy. The proposed method achieved accuracy of 100%, 100%, and 99.49% over Dataset-66, Dataset-160, and Dataset-255, respectively. The offline learning cost 208.2510 s for Dataset-255, and merely 0.053s for online prediction. (Conclusion) The proposed WE + HBP-FNN method achieves nearly perfect detection pathological brains in MRI scanning.
109 citations
TL;DR: In this article, a frequency-diverse compressive metamaterial aperture imager is proposed, which consists of a parallel plate waveguide, in which an array of complementary, resonant metammaterial elements is patterned into one of the plates.
Abstract: The resolution of a frequency diverse compressive metamaterial aperture imager is investigated. The aperture consists of a parallel plate waveguide, in which an array of complementary, resonant metamaterial elements is patterned into one of the plates. Microwaves injected into the waveguide leak out through the resonant metamaterial elements, forming a spatially diverse waveform at the scene. As the frequency is scanned, the waveforms change, such that scene information can be encoded onto a set of frequency measurements. The compressive nature of the metamaterial imager enables image reconstruction from a significantly reduced number of measurements. We characterize the resolution of this complex aperture by studying the simulated point spread function (PSF) computed using different image reconstruction techniques. We compare the imaging performance of the system with that expected from synthetic aperture radar (SAR) limits.
99 citations
TL;DR: The Fast Irregular Antenna Field Transformation Algorithm (FIAFTA) as discussed by the authors is a spectral domain representation of irregular field transformations with propagating plane waves on the Ewald sphere.
Abstract: Electromagnetic field transformations are important for electromagnetic simulations and for measurements. Especially for field measurements, the influence of the measurement probe must be considered, and this can be achieved by working with weighted field transformations. This paper is a review paper on weighted field transformations, where new information on algorithmic properties and new results are also included. Starting from the spatial domain weighted radiation integral involving free space Green's functions, properties such as uniqueness and the meaning of the weighting function are discussed. Several spectral domain formulations of the weighted field transformation integrals are reviewed. The focus of the paper is on hierarchical multilevel representations of irregular field transformations with propagating plane waves on the Ewald sphere. The resulting Fast Irregular Antenna Field Transformation Algorithm (FIAFTA) is a versatile and efficient transformation technique for arbitrary antenna and scattering fields. The fields can be sampled at arbitrary irregular locations and with arbitrary measurement probes without compromising the accuracy and the efficiency of the algorithm. FIAFTA supports different equivalent sources representations of the radiation or scattering object: 1) equivalent surface current densities discretized on triangular meshes, 2) plane wave representations, 3) spherical harmonics representations. The current densities provide for excellent spatial localization and deliver most diagnostics information about the test object. A priori information about the test object can easily be incorporated, too. Using plane wave and spherical harmonics representations, the spatial localization is not as good as with spatial current densities, but still much better than in the case of conventional modal expansions. Both far-field based expansions lead to faster transformations than the equivalent currents and in particular the orthogonal spherical harmonics expansion is a very attractive and robust choice. All three expansions are well-suited for efficient echo suppression by spatial filtering. Various new field transformation and new computational performance results are shown in order to illustrate some capabilities of the algorithm.
90 citations
TL;DR: In this article, an extremely thin dielectric metasurface is used to reshape the wavefronts distorted by a scatterer in order to mimic the reflection pattern of a flat ground plane.
Abstract: We demonstrate a novel and simple geometrical approach to cloaking a scatterer on a ground plane. We use an extremely thin dielectric metasurface to reshape the wavefronts distorted by a scatterer in order to mimic the reflection pattern of a flat ground plane. To achieve such carpet cloaking, the reflection angle has to be equal to the incident angle everywhere on the scatterer. We use a graded metasurface and calculate the required phase gradient to achieve cloaking. Our metasurface locally provides additional phase to the wavefronts to compensate for the phase difference amongst light paths induced by the geometrical distortion. We design our metasurface in the microwave range using highly sub-wavelength dielectric resonators. We verify our design by full-wave time-domain simulations using micro-structured resonators and show that results match theory very well. This approach can be applied to hide any scatterer under a metasurface of class C 1 (first derivative continuous) on a ground plane not only in the microwave regime, but also at higher frequencies up to the visible.
75 citations
TL;DR: In this paper, it was shown that stored energy defined from the difference between the energy density and the far field energy equals the energy expressions proposed by Vandenbosch for many but not all cases.
Abstract: Decomposition of the electromagnetic energy into its stored and radiated parts is instrumental in the evaluation of antenna Q and the corresponding fundamental limitations on antennas. This decomposition is not unique and there are several proposals in the literature. Here, it is shown that stored energy defined from the difference between the energy density and the far field energy equals the energy expressions proposed by Vandenbosch for many but not all cases. This also explains the observed cases with negative stored energy and suggests a possible remedy to them. The results are compared with the classical explicit expressions for spherical regions where the results only differ by the electrical size ka that is interpreted as the far-field energy in the interior of the sphere.
61 citations
TL;DR: This work investigates an adaptive, parallel and scalable integral equation solver for very large-scale electromagnetic modeling and simulation and proposes an additive Schwarz domain decomposition method for the efficient and robust solution of linear systems resulting from discontinuous Galerkin discretizations.
Abstract: This work investigates an adaptive, parallel and scalable integral equation solver for very large-scale electromagnetic modeling and simulation. A complicated surface model is decomposed into a collection of components, all of which are discretized independently and concurrently using a discontinuous Galerkin boundary element method. An additive Schwarz domain decomposition method is proposed next for the efficient and robust solution of linear systems resulting from discontinuous Galerkin discretizations. The work leads to a rapidly-convergent integral equation solver that is scalable for large multi-scale objects. Furthermore, it serves as a basis for parallel and scalable computational algorithms to reduce the time complexity via advanced distributed computing systems. Numerical experiments are performed on large computer clusters to characterize the performance of the proposed method. Finally, the capability and benefits of the resulting algorithms are exploited and illustrated through different types of real-world applications on high performance computing systems.
32 citations
TL;DR: In this article, the authors developed the method of broadband Green's function with low-wavenumber extraction (BBGFL) for arbitrary shaped waveguide for broadband simulations of vias in printed circuit boards (PCB).
Abstract: In this paper we developed the method of broadband Green's function with low wavenumber extraction (BBGFL) for arbitrary shaped waveguide. The case of Neumann boundary condition is treated. The BBGFL has the advantage that when using it to solve boundary value problems in a waveguide, the boundary conditions have been satisfied already. The broadband Green's function is expressed in modal expansion of modes that are frequency independent. To accelerate the convergence of the Green's function, a low wavenumber extraction is performed. The singularity of the Green's function is also extracted by such low wavenumber extraction. Numerical results show that BBGLF and direct MoM are in good agreement. We next illustrate the application of BBGFL for broadband simulations of vias in printed circuit boards (PCB) by combining with the method of Foldy-Lax multiple scattering equation. The results show that BBGFL are in good agreement with MoM and HFSS. It is also shown that BBGFL is many times faster than direct MoM and HFSS. The computational efficiency in broadband simulations makes this technique useful for fast computer-aided design (CAD). The effects of waveguide or cavity structures are critical for the electrical performance of electronic devices and components in signal integrity (SI), power integrity (PI), electromagnetic interference (EMI), and electromagnetic compatibility (EMC). Harmful electromagnetic signal noises or interferences are often generated and amplified at the resonant frequencies of the waveguide or cavity structures. The issues deteriorate when the electronic devices or computer systems operate at higher frequency or faster speed. In printed circuited boards (PCBs), two adjacent power/ground planes form a waveguide/cavity structure. The propagating modes satisfy the PMC (Neumann boundary conditions) at the edges of PCB power/ground plane structures. The power/ground plane structures are the key root causes in SI/PI and EMI/EMC problems. Vias are used for vertical interconnects for multilayer PCBs. At frequencies near the resonant frequencies, the propagating electromagnetic waves excite resonant modes, that result in strong edge radiations. These cause EMI/EMC problems. The switching noises induced by voltage regulator module (VRM) generate voltage fluctuations and lead to PI problems. The high frequency power noise can also couple into signal vias and cause SI/PI coupling issues. Therefore, the modeling of PCB cavity with vias is critical in practical designs and applications of high speed PCBs and packages. Fast and accurate modeling technique is desired for broadband simulations in electronic design and application. The finiteness of the parallel power/ground planes make them waveguide/cavity structures. The power/ground planes are also of arbitrary shape. Commercial tools such as HFSS provide solutions for the analysis of the via-cavity coupling problem. The tools require large CPU and memory and are not suited for broadband analysis. The physical problem is that of TM modes in a cavity with PMC boundary conditions on the side walls. Various methods have been used for waveguide
32 citations
TL;DR: In this article, the authors apply the method of the Broadband Green's Functions with Low Wavenumber Extraction (BBGFL) to calculate band diagrams in periodic structures and apply the BBGFL to the surface integral equation and the Method of Moments gives a linear eigenvalue equation that gives the broadband solutions simultaneously for a given point in the first Brillouin zone.
Abstract: We apply the method of the Broadband Green's Functions with Low wavenumber extraction (BBGFL) to calculate band diagrams in periodic structures. We consider 2D impenetrable objects placed in a 2D periodic lattice. The low wavenumber extraction is applied to the 2D periodic Green's function for the lattice which is used to formulate the surface integral equation. The low wavenumber extraction accelerates the convergence of the Floquet modes expansion. Using the BBGFL to the surface integral equation and the Method of Moments gives a linear eigenvalue equation that gives the broadband (multi-band) solutions simultaneously for a given point in the first Brillouin zone. The method only requires the calculation of the periodic Green's function at a single low wavenumber. Numerical results are illustrated for the 2D hexagonal lattice to show the computational efficiency and accuracy of the method. Because of the acceleration of convergence, an eigenvalue problem with dimensions 49 plane wave Floquet modes are sufficient to give the multi-band solutions that are in excellent agreement with results of the Korringa Kohn Rostoker (KKR) method. The multiband solutions for the band problem and the complementary band problem are also discussed.
27 citations
TL;DR: A novel method which attempts to communicate at carrier frequency much higher than the plasma cutoff frequency to overcome the highly dynamic channel characteristics and enable adaptive transmission is proposed.
Abstract: The radio blackout problem stands as one long obstacle for hypersonic flight and planetary atmosphere reentry. Rather than previous physical mitigation methods aiming to reduce the plasma electron density, this paper proposes a novel method which attempts to communicate at carrier frequency much higher than the plasma cutoff frequency. To overcome the highly dynamic channel characteristics, the reflected wave is used online to estimate the instantaneous channel states and enable adaptive transmission. According to the predicted channel states, the plasma sheath induced phase shift and amplitude attenuation are compensated by baseband modulation and power adaptation, respectively. Numerical simulations are presented and discussed, in order to illustrate the effectiveness of the proposed method.
27 citations
TL;DR: In this paper, a planar dual-mode metamaterial (MTM) antenna using rectangular type complementary split ring resonator (CSRR) is proposed, which achieves simulated antenna gain of 2.60 dB with 70% radiation efficiency.
Abstract: In this paper a compact planar dual-mode metamaterial (MTM) antenna using rectangular type complementary split ring resonator (CSRR) is proposed. It is observed that an increase in series capacitance tends to decrease resonant frequency at which n = 1 mode is obtained in the proposed antenna. Zeroth order mode (ZOR) is obtained by means of rectangular type CSRR, tends to provide the miniaturized area. Dispersion relations are shown in order to characterize the metamaterial behavior by extracting the equivalent circuit parameters. The resonant frequency of the antenna is 2.14 GHz with input reflection coefficient up to −45 dB. The electrical size of the proposed MTM antenna is 0.321λ0 × 0.285λ0 × 0.011λ0. ZOR mode is observed at 1.15 GHz although the proposed antenna is operated at 2.14 GHz. Furthermore, it achieves simulated antenna gain of 2.60 dB with 70% radiation efficiency. In order to verify the simulation results of antenna, a prototype is fabricated and measured.
TL;DR: In this article, a circularly polarized (CP) high efficiency wide band reflectarray (RA) antenna is designed for Ka-band using cross bow-tie elements, which provides high gain, high aperture efficiency, wideband axial ratio (AR), in circularly polarized bowtie RA using multiple copies of unit cell to form 25 ∗ 25 antenna array.
Abstract: A Circularly Polarized (CP) high efficiency wide band Reflectarray (RA) antenna is designed for Ka-band using cross bow-tie elements. The reflected wave phase curve is obtained by anti-clockwise bow-tie rotation. The linear phase curve with complete 360 ◦ degree is obtained when left-hand circularly polarized (LHCP) is incident normally in unit cell environment. The proposed method provides high gain, high aperture efficiency, wideband axial ratio (AR), in circularly polarized bow-tie RA using multiple copies of unit cell to form 25 ∗ 25 antenna array. Before designing RA, the unitcell is analyzed, for oblique incidence to predict its bandwidth. The proposed antenna provided good performance in terms of Half Power Beam width (HPBW), Side Love Level (SLL), cross polarization, gain bandwidth and AR bandwidth. A 25 ∗ 25 bow-tie RA antenna provides the highest aperture efficiency of 57%, HPBW of 9.0 degrees, SLL −19 dB, cross polarization −27 dB. A 1-dB gain bandwidth of 32.5%, 3- dB gain bandwidth of 51.4% and 1.5-dB AR bandwidth of 32.9% while 3-dB AR bandwidth of 48.7% is achieved in simulation. These results are validated through fabricated cross bow-tie RA, and the measurements make good agreement with simulation results.
TL;DR: In this article, the authors applied the finite element method (FEM) to solve the EEG forward problem and solved the singularity due to punctual dipole sources and the numerical errors observed near the interface of different tissues.
Abstract: The finite-element method (FEM) is applied to solve the EEG forward problem. Two issues related to the implementation of this method are investigated. The first is the singularity due to the punctual dipole sources and the second is the numerical errors observed near the interface of different tissues. To deal with the singularity of the punctual dipole sources, three source modeling methods, namely, the direct, the subtraction and the Saint Venant's methods, are examined. To solve the problem of numerical instability near the interface of different tissues, a modification on the Saint Venant's method is introduced. The numerical results are compared with analytical solution in the case of the multilayer spherical head models. The advantages of the proposed method are highlighted.
TL;DR: In this article, a numerical solution of nonlinear ferromagnetic problems is formulated using the three-dimensional time-domain finite element method (TDFEM) combined with the inverse JilesAtherton (J-A) vector hysteresis model.
Abstract: In this work, a numerical solution of nonlinear ferromagnetic problems is formulated using the three-dimensional time-domain finite element method (TDFEM) combined with the inverse JilesAtherton (J-A) vector hysteresis model. After a brief introduction of the J-A constitutive model, the second-order nonlinear partial differential equation (PDE) is constructed through the magnetic vector potential in the time domain, which is then discretized by employing the Newmark-β scheme, and solved by applying the Newton-Raphson method. Different Newton-Raphson schemes are constructed and compared. The capability of the proposed methods is demonstrated by several numerical examples including the simulation of the physical demagnetization process, the prediction of the magnetic remanence in the ferromagnetic material, and the generation of higher-order harmonics.
TL;DR: In this article, a new circularly-polarized metasurfaced dipole antenna (MSDA) with wide axial-ratio (AR) beamwidth and radar cross section (RCS) reduction properties is proposed and studied.
Abstract: A new circularly-polarized metasurfaced dipole antenna (MSDA) with wide axial-ratio (AR) beamwidth and radar cross section (RCS) reduction properties is proposed and studied in this paper. This antenna is a quite simple half-wavelength linear dipole right above a metasurface which consists of 9 double-head arrow-shaped unit cells arranged in a 3×3 layout. By cautiously choosing the geometrical parameters of the metasurface and tuning the distance between the dipole and the metasurface, the whole structure turns out to be a circularly-polarized antenna with RCS reduction feature. Simulation results show that the MSDA in circular polarization achieves an operating bandwidth of 410MHz and a wide AR beamwidth of 123◦ and 90◦ in φ = 0◦ and φ = 90◦ planes respectively, together with a maximum RCS reduction of 10.4 dB in the whole operating band.
TL;DR: In this paper, a nonlinear electromagnetic inverse scattering problem on sparse investigation domains is solved using nonlinear Landweber iterations, where at each iteration a thresholding function is applied to enforce the sparseness-promoting L0/L1-norm constraint.
Abstract: A scheme for efficiently solving the nonlinear electromagnetic inverse scattering problem on sparse investigation domains is described. The proposed scheme reconstructs the (complex) dielectric permittivity of an investigation domain from fields measured away from the domain itself. Least-squares data misfit between the computed scattered fields, which are expressed as a nonlinear function of the permittivity, and the measured fields is constrained by the L0/L1-norm of the solution. The resulting minimization problem is solved using nonlinear Landweber iterations, where at each iteration a thresholding function is applied to enforce the sparseness-promoting L0/L1-norm constraint. The thresholded nonlinear Landweber iterations are applied to several two-dimensional problems, where the "measured" fields are synthetically generated or obtained from actual experiments. These numerical experiments demonstrate the accuracy, efficiency, and applicability of the proposed scheme in reconstructing sparse profiles with high permittivity values.
TL;DR: In this paper, the authors presented an extremely sub-wavelength negative index metamaterial structure operating at radio frequency, which consists of planar spiral and meandering wire structures separated by dielectric substrate.
Abstract: We present an extremely sub-wavelength negative index metamaterial structure operating at radio frequency. The unit cell of the metamaterial consists of planar spiral and meandering wire structures separated by dielectric substrate. The ratio of the free space wavelength to unit cell size in the propagation direction is record breaking 1733 around the resonance frequency. The proposed metamaterial also possesses the most extreme refractive index of −109 that has been recorded to date. Underlying magnetic and electric response originate from the spiral and meandering wire, respectively. We show that the meandering wire is the key element to improve the transparency of the negative index metamaterial.
TL;DR: In this article, the Discontinuous Galerkin Method (DGM) forward solver with a number of features that aim to benefit tomographic microwave imaging algorithms is presented.
Abstract: Novel microwave imaging systems require flexible forward solvers capable of incorporating arbitrary boundary conditions and inhomogeneous background constitutive parameters. In this work we focus on the implementation of a time-harmonic Discontinuous Galerkin Method (DGM) forward solver with a number of features that aim to benefit tomographic microwave imaging algorithms: locally varying high-order polynomial field expansions, locally varying high-order representations of the complex constitutive parameters, and exact radiating boundary conditions. The DGM formulated directly from Maxwell's curl equations facilitates including both electric and magnetic contrast functions, the latter being important when considering quantitative imaging with magnetic contrast agents. To improve forward solver performance we formulate the DGM for time-harmonic electric and magnetic vector wave equations driven by both electric and magnetic sources. Sufficient implementation details are provided to permit existing DGM codes based on nodal expansions of Maxwell's curl equations to be converted to the wave equation formulations. Results are shown to validate the DGM forward solver framework for transverse magnetic problems that might typically be found in tomographic imaging systems, illustrating how high-order expansions of the constitutive parameters can be used to improve forward solver performance.
TL;DR: In this article, an optical surface transformation (OST) method is proposed, which does not need to consider what kinds of coordinate transformation should be used when designing a novel device, but only need to choose the shapes of two end surfaces (namely, the input and output surfaces of the device), which are linked by an optic-null medium (ONM) that is a highly anisotropic homogeneous medium.
Abstract: An optical surface transformation (OST) method is proposed briefly in this short paper. Compared with Transformation Optics (TO), we do not need to consider what kinds of coordinate transformation should be used when designing a novel device, but only need to choose the shapes of two end surfaces (namely, the input and output surfaces of the device), which are linked by an optic-null medium (ONM) that is a highly anisotropic homogeneous medium. All devices designed by OST can be realized by some ONM. The design process of an optical device with some pre-designed function can be converted to the simple choice of the shape and size of the optical surfaces with the OST, which will become a simple and yet innovative way to design electromagnetic/optical devices.
TL;DR: In this article, the authors present an alternative method of calculation based on the force formula of Weber-Ritz and which does not involve, directly, the field entities E and B, nor the leakage flux from the solenoid or the vector potential.
Abstract: The deflection of charged particle beams by electric and/or magnetic fields is invariably based on the field centred approach associated with Maxwell-Lorentz and incorporated into the Lorentz force formula Here we present an alternative method of calculation based on the force formula of Weber-Ritz and which does not involve, directly, the field entities E and B In this study we evaluate the deflection of an electron beam by a long solenoid carrying direct current and positioned centrally across the beam The experiment has some bearing on the Aharonov-Bohm effect in that our calculations indicate that even for very long solenoids the classical force on the beam remains finite The standard interpretation of the effect is, however, in terms of quantum mechanics and vector potential Experimental measurements have been made of electron beam deflections by three solenoids, 025 m, 050 m and 075 m long; each solenoid is doubly wound with the same winding density (2600 turns per metre) and carrying the same current of 500 A dc Our results indicate that, within the limits of experimental error, both Weber-Ritz and Maxwell-Lorentz theories correlate with measurements for the longer solenoids However in the case of the shortest solenoid, the lack of uniformity of the magnetic field, leads to significant error in the calculation of beam deflection by the Lorentz force By contrast in a Weber-Ritz calculation a precise value of beam deflection is obtained by equating the impulse of the non uniform beam force to the vertical momentum change of the electron This is a fundamentally different approach which uses a statistical summation of forces on the beam in terms of relative velocities between moving electrons and involves a direct computation of the vertical force on the beam due to the circling solenoid current This method has distinct advantages in terms of economy; that is, it does not involve directly field entities E and B, nor the leakage flux from the solenoid or the vector potential
TL;DR: In this paper, numerical analysis of nonlinear ferromagnetic problems is presented using the three-dimensional time-domain flnite element method (TDFEM), where the second-order nonlinear partial difierential equation (PDE) combined with the inverse Jiles-Atherton (J-A) vector hysteresis model is solved in the time domain with the Newton- Raphson method.
Abstract: In this work, numerical analysis of nonlinear ferromagnetic problems is presented using the three-dimensional time-domain flnite element method (TDFEM). Formulated with the second- order nonlinear partial difierential equation (PDE) combined with the inverse Jiles-Atherton (J-A) vector hysteresis model, the nonlinear problems are solved in the time domain with the Newton- Raphson method. To solve the ordinary difierential equation (ODE) representing the magnetic hysteresis accurately and e-ciently, several ODE solvers are speciflcally designed and investigated. To improve the computational e-ciency of the Newton-Raphson method, the multi-dimensional secant methods, aka Broyden's methods, are incorporated in the nonlinear TDFEM solver. A nonuniform time-stepping scheme is also developed using the weighted residual approach to remove the requirement of a uniform time-step size during the simulation. The capability and the performance of the proposed methods are demonstrated by various numerical examples.
TL;DR: In this paper, a three-layer structure is designed and manufactured, which involves a resistive frequency selective surface (FSS) sandwiched between two layers of magnetic sheets, and the measurement results reveal that this structure exhibits −13 dB reflectivity in the frequency range of 7.9-18 GHz while the thickness is only 1.7 mm.
Abstract: To achieve broadband microwave absorption, a three-layer structure is designed and manufactured. It involves a resistive frequency selective surface (FSS) sandwiched between two layers of magnetic sheets. The measurement results reveal that this structure exhibits −13 dB reflectivity in the frequency range of 7.9-18 GHz while the thickness is only 1.7 mm. The reflectivity bandwidth at the level of −10 dB is 11.4 GHz which is much wider than that of magnetic sheets with non-resistive FSS or the magnetic sheets without FSS. The effect of resistive FSS on the performance of the multilayered absorber is discussed in detail. It is concluded that an embedded resistive double loops FSS can result in a secondary resonance peak which obviously broadens the reflectivity bandwidth of the magnetic sheets.
TL;DR: In this article, the authors demonstrate a device that is capable of generating an ultrashort (sub-nanosecond) high power microwave pulse by means of passive pulse compression in a compact reverberant cavity.
Abstract: In this paper, we demonstrate a device that is capable of generating an ultrashort (sub-nanosecond) high power microwave pulse by means of passive pulse compression in a compact reverberant cavity. The long duration input pulse into the cavity is created using time-reversal techniques, which allows the waveform to contain the inverse profile of the cavity phase distortion. When fed back into the cavity, the wave focusing at the output port results in a compressed ultrashort pulse with enhanced peak amplitude. We experimentally demonstrate a pulse compressor consisting of a 0.0074 m 3 cavity capable of generating a 130 picosecond pulse from an input waveform of 300 nanosecond duration with the peak gain of up to 19 dB.
TL;DR: In this paper, a non-rare-earth axial-field magnetic variable gear (MVG) was proposed for real-time changing the numbers of permanent magnet (PM) pole-pairs in the input and output rotors.
Abstract: This paper presents a new non-rare-earth axial-field magnetic variable gear (MVG). By real-time changing the numbers of permanent magnet (PM) pole-pairs in the input and output rotors, the gear ratio becomes controllable. The key is to propose a new stationary ring integrated with magnetizing windings in such a way that various PM pieces can be independently magnetized to form different pole-pair numbers. After introducing the unique features of the non-rare-earth PM material aluminum-nickel-cobalt (AlNiCo), the proposed topology and design principle are discussed. By using finite element analysis, the electromagnetic performances of the proposed MVG under different gear ratios are analyzed. In particular, the corresponding torque transmission capability is assessed, and the influence caused by the introduction of the magnetizing windings is discussed. Hence, the validity of the proposed MVG can be verified.
TL;DR: In this paper, the influence of collision frequency, anisotropy factor and angle of inclination of prolate irregularities of electron density fluctuations with respect to the geomagnetic field of lines on the broadening of the spatial power spectrum is analyzed.
Abstract: General dispersion equation is obtained at arbitrary inclination angles of the external magnetic field and wave vector of an incident EM wave. Statistical characteristics of the phase fluctuations of scattered high frequency EM waves in the collision magnetized plasma caused by electron density and external magnetic field fluctuations taking into account polarization coefficients for both ordinary and extraordinary waves are calculated analytically. The influence of collision frequency, anisotropy factor and angle of inclination of prolate irregularities of electron density fluctuations with respect to the geomagnetic field of lines on the broadening of the spatial power spectrum is analyzed. Phase portraits of the phase fluctuations caused by the geomagnetic field fluctuations are constructed at different spatial parameters characterizing magnetic field and electron density fluctuations. Numerical calculations are carried out for the ionospheric F -region parameters using experimental data.
TL;DR: This work presents an algorithm that exploits the sequential way in which the subdomains are usually placed for layered structures in packaging problems, and a reordering of interface and volume unknowns combined with a block LDU (Lower-Diagonal-Upper) decomposition allows improvements in terms of memory cost and time of execution, with respect to previous DGTD implementations.
Abstract: The discontinuous Galerkin's (DG) method is an efficient technique for packaging problems. It divides an original computational region into several subdomains, i.e., splits a large linear system into several smaller and balanced matrices. Once the spatial discretization is solved, an optimal time integration method is necessary. For explicit time stepping schemes, the smallest edge length in the entire discretized domain determines the maximal time step interval allowed by the stability criterion, thus they require a large number of time steps for packaging problems. Implicit time stepping schemes are unconditionally stable, thus domains with small structures can use a large time step interval. However, this approach requires inversion of matrices which are generally not positive definite as in explicit shemes for the first-order Maxwell's equations and thus becomes costly to solve for large problems. This work presents an algorithm that exploits the sequential way in which the subdomains are usually placed for layered structures in packaging problems. Specifically, a reordering of interface and volume unknowns combined with a block LDU (Lower-Diagonal-Upper) decomposition allows improvements in terms of memory cost and time of execution, with respect to previous DGTD implementations.
TL;DR: In this paper, the problem of electromagnetic waves radiation by an impedance vibrator located over finitedimensional perfectly conducting screen is solved using asymptotic expressions for the current in a horizontal impedance vibrators placed over an infinite plane, obtained by averaging method.
Abstract: A problem of electromagnetic waves radiation by an impedance vibrator located over finitedimensional perfectly conducting screen is solved. The vibrator may have surface impedance distributed over its length. The solution is derived using asymptotic expressions for the current in a horizontal impedance vibrator placed over an infinite plane, obtained by averaging method. The problem was solved provided that the diffracted fields from the edges of the screen have little effect on the vibrator current amplitude, i.e., if the screen dimensions are comparable to or larger than the wavelength. Full radiation fields in all observation space in the far zone were found by the uniform geometrical theory of diffraction. The vibrator dimensions, value and type of surface impedance, removing from the screen and screen sizes were used as parameters. The multivariable electrodynamic characteristics of the resonant impedance vibrators placed above an infinite plane and square screen were studied. Characteristics dependences upon the vibrator dimensions, value and type of the surface impedance, removing from the screen, and screen dimensions were obtained.
TL;DR: In this paper, a dual-band multiple-input-multiple-output (MIMO) antenna system for LTE 700/2300/2500, UMTS2100, GSM 1800/1900 mobile phone applications is presented.
Abstract: A dual-band multiple-input-multiple-output (MIMO) antenna system for LTE 700/2300/2500, UMTS2100, GSM 1800/1900 mobile phone applications is presented. The whole system consists of four identical 3-D IFAs (inverted F antenna) loaded with lumped inductors and folded on FR4 cuboids. Without any special designed decoupling structures, the measured isolation among antenna elements is higher than 13 dB. Return loss characteristics, correlation coefficient, gain and radiation performance are also presented.
TL;DR: In this paper, an advanced integral equation model is presented by giving its general framework of model developments, model expressions, and predictions of bistatic scattering for various surface parameters, including the transition function for the Fresnel reflection coefficient.
Abstract: This paper deals with the modeling of bistatic scattering from a randomly rough surface. An advanced integral equation model is presented by giving its general framework of model developments, model expressions, and predictions of bistatic scattering for various surface parameters. Extension work to improve the model accuracy is also reported in more detail. In particular, the transition function for the Fresnel reflection coefficient is in more general form. Model predictions are illustrated, demonstrated, and validated by extensive comparisons with numerical simulations. The updated advanced integral equation model remains a compact algebraic form for single scattering and substantially improves prediction accuracy in bistatic scattering that is drawing more emerging applications in earth remote sensing.