Surface Current Density Research Articles

An Effective Math Model for Eliminating Interior Resonance Problems of EM Scattering

It is well-known that if an E-field integral equation or an H-field integral equation is applied alone in analysis of EM scattering from a conducting body, the solution to the equation will be either nonunique or unstable at the vicinity of a certain interior frequency. An effective math model is presented here, providing an easy way to deal with this situation. At the interior resonant frequencies, the surface current density is divided into two parts: an induced surface current caused by the incident field and a resonance surface current associated with the interior resonance mode. In this paper, the presented model, based on electric field integral equation and orthogonal modal theory, is used here to filter out resonant mode; therefore, unique and stable solution will be obtained. The proposed method possesses the merits of clarity in concept and simplicity in computation. A good agreement is achieved between the calculated results and those obtained by other methods in both 2D and 3D EM scattering.

Differential conductance of an electrolytic cell in the presence of deposition of a coating material on the electrode

The influence of the deposition of a coating material on the electrode surface in an electrochemical cell on the current–voltage characteristics is investigated. The surface covering of particles is evaluated from the surface current density of the ions. The current–voltage characteristics for the cases when the surface deposition increases or reduces the surface resistance of the electrode are derived. The differential conductance, defined as the derivative of the current with respect to the applied voltage, is evaluated. The cases of small and large overpotential are considered. An extension of the model to a real situation in which the external potential applied to the cell is a step of a given amplitude is also considered.

Inhibition Effect of Guar Gum on the Corrosion Behaviour of Carbon Steel (K-55) in Fracturing Fluid

The inhibition effect of guar gum on carbon steel (K-55) in the simulated fracturing fluid under static conditions was studied. The electrochemical experimental results indicated that the carbon steel shows active dissolution behaviour in the absence and the presence of the inhibitor. However, guar gum, acting as mixed-type inhibitor, was swiftly able to promote the formation of a product layer onto the metal surface, lowering both cathodic and anodic current density. Electrochemical impedance spectroscopy (EIS) measurements were consistent with the polarisation curves, showing an improvement of the corrosion resistance of the carbon steel in the presence of the inhibitor. However, for long exposure times, the corrosion activity of the metal increases, as result of the breakdown of the corrosion product layer and initiation of localised corrosion spot. After both polarisation and EIS measurements, two different layers were observed. A thin, dark stable layer of magnetite and, for long holding times, a porous red layer, poorly adhered, of hematite. The hematite layer, due to its porous nature, was characterised by poor corrosion ability.

Effect of the Electrolyte Temperature and the Current Density on a Layer Microhardness Generated by the Anodic Aluminium Oxidation

The paper investigates the influence of the chemical composition and temperature of electrolyte, the oxidation time, voltage, and the current density on Vickers microhardness of aluminium oxide layers, at the same time. The layers were generated in the electrolytes with different concentrations of sulphuric and oxalic acids and surface current densities 1 A·dm−2, 3 A·dm−2, and 5 A·dm−2. The electrolyte temperature varied from −1.78°C to 45.78°C. The results have showed that while increasing the electrolyte temperature at the current density of 1 A·dm−2, the increase in the layer microhardness values is approximately by 66%. While simultaneously increasing the molar concentration of H2SO4in the electrolyte, the growth rate of the microhardness value decreases. At the current density of 3 A·dm−2, by increasing the electrolyte temperature, a reduction in the microhardness of the generated layer occurs with the anodic oxidation time less than 25 min. The electrolyte temperature is not significant with the changing values of the layer microhardness at voltages less than 10.5 V.

14-3-3τ Promotes Surface Expression of Cav2.2 (α1B) Ca2+ Channels

Surface expression of voltage-gated Ca(2+) (Cav) channels is important for their function in calcium homeostasis in the physiology of excitable cells, but whether or not and how the α1 pore-forming subunits of Cav channels are trafficked to plasma membrane in the absence of the known Cav auxiliary subunits, β and α2δ, remains mysterious. Here we showed that 14-3-3 proteins promoted functional surface expression of the Cav2.2 α1B channel in transfected tsA-201 cells in the absence of any known Cav auxiliary subunit. Both the surface to total ratio of the expressed α1B protein and the current density of voltage step-evoked Ba(2+) current were markedly suppressed by the coexpression of a 14-3-3 antagonist construct, pSCM138, but not its inactive control, pSCM174, as determined by immunofluorescence assay and whole cell voltage clamp recording, respectively. By contrast, coexpression with 14-3-3τ significantly enhanced the surface expression and current density of the Cav2.2 α1B channel. Importantly, we found that between the two previously identified 14-3-3 binding regions at the α1B C terminus, only the proximal region (amino acids 1706-1940), closer to the end of the last transmembrane domain, was retained by the endoplasmic reticulum and facilitated by 14-3-3 to traffic to plasma membrane. Additionally, we showed that the 14-3-3/Cav β subunit coregulated the surface expression of Cav2.2 channels in transfected tsA-201 cells and neurons. Altogether, our findings reveal a previously unidentified regulatory function of 14-3-3 proteins in promoting the surface expression of Cav2.2 α1B channels.

ELECTROMAGNETIC FIELD TRANSFORMATIONS FOR MEASUREMENTS AND SIMULATIONS (Invited Paper)

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.

Research on Electromagnetic Engineering and Technology with Application of EFIT Code in J-TEXT Tokamak

The Grad-Shafranov equation is solved by EFIT code in J-TEXT tokamak. In this paper, it applies EFIT code to analyze the evolution of some plasma parameters during the discharge of J-TXET tokamak. Through plasmas balance calculation, the pressure of plasmas, internal magnetic surface and plasma current density profile are given. It provides important reference data for the operation and control of the J-TXET tokamak discharge.

A study of cogging torque in permanent magnet synchronous machines with fractional slot windings

Results of an investigation of cogging torque in permanent magnet synchronous machines with fractional slot windings are given, and the nature of their origin is considered. This research is important because of the necessity to assess cogging torque at the stage of design of machines developed for areas of application in which there are rigid requirements for noise and vibration level. To simplify the solution, the design of an electrical machine with radial location of magnets is chosen as am object of research. A formula of cogging torque determined as the result of interaction between magnetic field harmonics and corresponding harmonics of the surface current density is developed. Conditions required for cogging torque are determined. Equations for calculating the number of air gap permeance harmonics and magnetomotive force harmonics contributing to the generation of this cogging torque are presented. This study shows that the cogging torque has two components. The first component is the result of interaction of permeance and magnetic field harmonics having the same number; the second component is caused by interaction between the permeance harmonics and mixed harmonics of the magnetic field induced by the stator slotting. An experimental investigation of cogging torque in a machine with 12 slots and 10 poles has been conducted. Fourier analysis of the experimental data verifies the analytical results of experimental data.

Modelos relativistas de discos de polvo magnetizados en un espaciotiempo conformestático axialmente simétrico

An infinite family of new solutions of the Einstein-Maxwell equations for axially symmetric conformastatic spacetimes is presented. This family of solutions describe thin dust disks made of material sources with a surface conduction current. The solutions are obtained by expressing the metric function and the magnetic potential in terms of an auxiliary function which satisfies the Laplace equation, a characteristic property of the conformastatic spacetimes. By introducing then a finite discontinuity on the first derivatives of the metric tensor, solutions with a delta function type singularity with support on the hypersurface z = 0 are obtained, describing so infinitesimally thin disks of infinite extension. Then, the surface energy-momentum and the surface current density of the disk are obtained by using the formalism of tensorial distributions and their physical content is analyzed. It was found that the energy density behaves well everywhere, that the energy-momentum tensor satisfies all the energy conditions and that, although the discs are of infinite extension, their total mass is finite. Furthermore, it is found that the curvature quadratic scalars and the electromagnetic invariants are regular everywhere, so that the spacetime is free of singularities. Finally, in order to illustrate the behavior of the family of thin disks, we consider the model for the first family member and graphically analyzes the behavior of the surface energy density and the surface current density. © 2014. Acad. Colomb. Cienc. Ex. Fis. Nat. All rights reserved.

Analytical finite element matrix elements and global matrix assembly for hierarchical 3-D vector basis functions within the hybrid finite element boundary integral method

Abstract. A hybrid higher-order finite element boundary integral (FE-BI) technique is discussed where the higher-order FE matrix elements are computed by a fully analytical procedure and where the gobal matrix assembly is organized by a self-identifying procedure of the local to global transformation. This assembly procedure applys to both, the FE part as well as the BI part of the algorithm. The geometry is meshed into three-dimensional tetrahedra as finite elements and nearly orthogonal hierarchical basis functions are employed. The boundary conditions are implemented in a strong sense such that the boundary values of the volume basis functions are directly utilized within the BI, either for the tangential electric and magnetic fields or for the asssociated equivalent surface current densities by applying a cross product with the unit surface normals. The self-identified method for the global matrix assembly automatically discerns the global order of the basis functions for generating the matrix elements. Higher order basis functions do need more unknowns for each single FE, however, fewer FEs are needed to achieve the same satisfiable accuracy. This improvement provides a lot more flexibility for meshing and allows the mesh size to raise up to λ/3. The performance of the implemented system is evaluated in terms of computation time, accuracy and memory occupation, where excellent results with respect to precision and computation times of large scale simulations are found.

Minimum-energy coils for transcranial magnetic stimulation: application to focal stimulation.

In transcranial magnetic stimulation (TMS), the stimulation-coil current is typically increased from 0 to over 5000A in less than 100μs. At the peak current, the energy stored in the magnetic field is over 300J. Thus, the average power during a pulse exceeds 3MW; the stimulator needs to be built from high-power electronics. The power requirements often limit the duration and frequency of repetitive TMS, for example, via coil heating. We introduce a method for finding the minimum-energy solution for a TMS coil with given focality constraints. This optimization is performed by using a spherically symmetric head model and by expressing the coil as a continuous surface current density, which is eventually discretized to form the coil windings. For the optimization, we defined TMS focality separately for the directions parallel and perpendicular to the field direction at the maximum of induced electric field. The computational model used for optimization was verified by manufacturing a prototype coil and measuring the electric field it induces in a spherically symmetric conductor. The optimized coil design requires significantly less power than existing TMS coil designs (a 73% reduction compared to an existing TMS coil with similar focality). The described method allows for more efficient, more focal TMS coils, which may reduce coil heating and the coil click.

Electromagnetic Scattering by a Perfectly Conducting Rectangular Plate Buried in a Lossy Half-Space

The aim of this paper is the accurate and efficient analysis of the electromagnetic scattering by an arbitrary oriented perfectly conducting rectangular plate entirely buried in a lossy half-space. The problem, formulated as an electric field integral equation (EFIE) in the spectral domain for the surface current density on the rectangular plate, is discretized by means of Galerkin's method with a set of orthonormal analytically Fourier transformable basis functions factorizing the behavior of the unknown at the edges. In this way, fast convergence is achieved even for scatterer size of some wavelengths. Unfortunately, this method leads to the numerical evaluation of infinite double integrals of oscillating and slowly decaying functions. To overcome this problem, a new analytical technique that allows to write such integrals as combinations of very quickly converging integrals is introduced.

Ultra-thin quadri-band metamaterial absorber based on spiral structure

We introduce a design of the metamaterial absorber (MA) consisting of spiral artificial inclusions printed on an ultra-thin dielectric layer backed by a metal plate. Both simulations and experiments show that the MA can achieve absorptions up to 96.49, 94.25, 98.94 and 92.04 % at 6.69, 8.70, 11.90 and 15.14 GHz, respectively. The surface current and power loss density of each absorption frequency were discussed to reveal the physical mechanism. Moreover, the proposed quadri-band MA possesses the advantages of being ultra-thin and polarization-insensitive and thus may find potential applications.

Point Matching Method를 이용한 접지된 유전체층 위의 저항띠 격자구조에 의한 TE 산란 해석

[Abstract] In this paper, the solutions of TE(transverse electric) scattering problems by a resistive strip grating over a grounded dielectric layer are analyzed by applying the PMM(point matching method) known as a numerical method of electromagnetic fileld. The boundary conditions are applied to obtain the unknown field coefficients and the resistive boundary condition is used for the relationship between the tangential magnetic field and the induced surface current density on the resistive strip. The induced surface current density of resistive strip is obtained by difference of the up and down of the magnetic field in two boundary areas of the resistive strip. The numerical results for reflected power of zeroth order mode analyzed by according as the resistivity, the width and spacing of resistive strip, the relative permittivity and thickness of dielectric layer, and incident angles. The numerical results shown in good agreement compared to those of the existing papers using FGMM(fourier galerkin moment method). Key word : TE scattering, Resistive boundary condition, Point matching method, Fourier Galerkin moment method.

Low-frequency and broadband metamaterial absorber based on lumped elements: design, characterization and experiment

In this paper, we propose and experimentally validate a low-frequency metamaterial absorber (MMA) based on lumped elements with broadband stronger absorptivity in the microwave regime. Compared with the electric resonator structure MMA, the composite MMA (CMMA) loaded with lumped elements has stronger absorptivity and nearly impedance-matched to the free space in a broadband frequency range. The simulated voltage in lumped elements and the absorbance under different substrate loss conditions indicate that incident electromagnetic wave energy is mainly transformed to electric energy in the absorption band with high efficiency and subsequently consumed by lumped resistors. Simulated surface current and power loss density distributions further clarify the mechanism underlying observed absorption. The CMMA also shows a polarization-insensitive and wide-angle strong absorption. Finally, we fabricate and measure the MMA and CMMA samples. The CMMA yields below −10 dB reflectance from 2.85 to 5.31 GHz in the experiment, and the relative bandwidth is about 60.3 %. This low-frequency microwave absorber has potential applications in many martial fields.

DC current induced second order optical nonlinearity in graphene.

We calculate the dc current induced second harmonic generation in doped graphene using the semiconductor Bloch equations under relaxation time approximations. We find that the maximum value of the effective second order susceptibility appears when the fundamental photon energy matches the chemical potential. For a surface current density 1.1 × 10(3) A/m and a relaxation time at optical frequencies of 13 fs, the effective second order susceptibility χeff(2);xxx can be as large as 10(-7)m/V for h̄ω = 0.2 eV or 10(-8) m/V for h̄ω = 0.53 eV.

Analytical Modeling of Graphene Ribbons as Optical Circuit Elements

We demonstrate that graphene ribbons can be modeled as circuit elements, which have dual capacitive-inductive nature. In the subwavelength regime, the surface current density on a single graphene ribbon subject to an incident p-polarized plane wave is derived analytically and then it is extended to coplanar arrays of graphene ribbons by applying perturbation theory. It is demonstrated that even isolated graphene ribbons have capacitive properties and the interaction between them in an array only changes the capacitance. Finally, we propose an accurate circuit model for the ribbon array by applying appropriate boundary conditions.

Study of X-ray radiation damage in the AGIPD sensor for the European XFEL

The European X-ray Free Electron Laser (XFEL), currently being constructed in Hamburg and planned to be operational in 2017 for users, will deliver 27,000 fully coherent, high brilliance X-ray pulses per second with duration less than 100 fs. The unique features of the X-ray beam pose major challenges for silicon detectors used at the European XFEL for imaging experiments, in particular a radiation tolerance of silicon sensors for doses up to 1 GGy for 3 years of operation at an operating voltage above 500 V.One of the detectors under development at the European XFEL is the Adaptive Gain Integrating Pixel Detector (AGIPD), which is a hybrid detector system with ASICs bump-bonded to p+n silicon pixel sensors. We have designed the silicon sensors for the AGIPD, which have been fabricated by SINTEF and delivered in the beginning of February 2013. To demonstrate the performance of the AGIPD sensor with regard to radiation hardness, mini-sensors with the same pixel and guard-ring designs as the AGIPD together with test structures have been irradiated at the beamline P11 of PETRA III with 8 keV and 12 keV monoenergetic X-rays to dose values up to 10 MGy. The radiation hardness of the AGIPD sensor has been proven and all electrical properties are within specification before and after irradiation. In addition, the oxide-charge density and surface-current density from test structures have been characterized as function of the X-ray dose and compared to previous measurements for test structures produced by four vendors.

ANALYSIS OF GREEN’S FUNCTION AND SURFACE CURRENT DENSITY FOR RECTANGULAR MICROSTRIP PATCH ANTENNA

In this paper, Green’s function and surface current density for planar structure has been calculated. The approach makes use of the popular and rigorously used spectral domain full wave analysis method in conjunction with method of moment as numerical analysis tool. In present approach, boundary conditions are applied at patch metallization, which leads to integral equation with the involvement of green’s function in spectral domain, which includes the effect of dielectric, conductor loss, surface wave modes and space wave radiation. By applying Galerkin’s moment method integral equation are transformed to linear set of equations. Entire domain basis function is used to improve the efficiency of the solution.

2개 유전체층 위의 완전도체띠 격자구조에 의한 TM 산란의 급속한 수렴 해

본 논문에서는 2개 유전체층 위의 완전도체띠 격자구조에 의한 TM (transverse magnetic)산란의 급속한 수렴 해에 대한 문제를 수치해석 방법인 FGMM (Fourier Galerkin moment method)를 이용하여 해석하였다. TM 산란에 대하여 유도되는 표면 전류밀도는 스트립 양 끝에서 매우 큰 값이 예측되므로, 이때 스트립에 유도되는 전류밀도는 적절한 모서리 경계조건을 만족하는 함수와 1종 Chebyshev 다항식의 곱의 급수로 전개하였다. 도체띠에 유도되는 전류밀도, 정규화된 반사전력 및 투과전력을 계산하였다. 제안된 함수를 사용한 수치결과는 기존의 지수함수를 사용했을 때 보다 빠르게 수렴도가 향상되었으며, 수치결과들은 기존 논문들의 결과들과 비교하여 거의 일치하였다. In this paper, the solutions of TM (transverse magnetic) scattering problems by perfectly conducting strip grating on two dielectric layers are analyzed by applying the FGMM (Fourier Galerkin moment method) as a numerical method. For the TM scattering problem, the induced surface current density is expected to the very high value at both edges of the strip, then the induced surface current density on the strip is expanded in a series of the multiplication of the functions of appropriate edge boundary condition and the Chebyshev polynomials of the first kind. The numerical results are obtained for the magnitude of induced current density, the normalized reflected power and transmitted power. The numerical results using proposed functions were improved the convergence faster than existing exponential functions, and the numerical results shown the good agreement compared to those of the existing papers.