Surface Current Density Research Articles

Generalized magnetostatic target field method for shielded magnetic field coils in a separable coordinate system.

A theoretical method is described to analytically calculate a pair of surface current densities, which produce a desired static magnetic field in one region of the space and zero magnetic field in another. The analysis is based on the known relationship between a surface current density and a stream function, the equivalence of stream functions and surface magnetic dipole density, and the scalar potential representation of the associated magnetic field in free space. From these relations, we formulate the magnetostatic problem, which is often treated as a vector field problem, as a scalar field problem in which a two-dimensional scalar field (stream function) is related to a three-dimensional one (magnetic scalar potential) via the differentiation of the electrostatic Green's function 1/|r-rs|. It is shown that, in a coordinate system in which a separated form of the Green's function exists (separable coordinate system), there exists a simple relationship between a harmonic component of a stream function and a harmonic component of the magnetic scalar potential. The method is applied to calculate idealized surface current patterns for actively shielded, linear gradient field coils in the Cartesian, cylindrical, and spherical coordinates.

Calculus of Variations Applied to Boundary Condition of Gangbuster Metasurface

In this letter, the calculus of variations is applied to boundary condition of the gangbuster metasurface based on assumed current distribution. In the theory, the radiated field from the periodic gangbuster metasurface can be deposed into a series of Floquet's modes, which results in an integral equation about the surface current density. Further, due to smaller periodicity than the operation wavelength, the zero-order reflection coefficient can be derived through its surface current distribution. Especially, the reflection coefficient is variably stable for the induced current distribution. In this case, an approximate sine current distribution is provided, yielding a high-accuracy expression of the reflection coefficient. Finally, the simulated results of the periodic metallic cut-lines support the proposed theory, regardless of the geometrical size and incidence angle. The theory provides a simple and accurate approach for the average boundary condition of the metasurface, greatly avoiding the difficulty of obtaining an accurate induced current of the metasurface under the incident field.

Microwave polarization conversion and reflection loss mechanism of complementary-modeled Rossler-based chaotic metamaterial

The complementary-modeled Rossler chaotic metamaterial (CRCM) with FR-4 dielectric layer is proposed to design metamaterial absorber with multi-resonance peaks. Under “master-slave” boundary condition in high-frequency structure simulator (HFSS) software, the electric field between adjacent boundaries presents phase difference which can simulate an infinite array. The research results show that the CRCM demonstrates multi-resonant peaks from 4 GHz to 10 GHz, and the area of metal patterned-layer can obviously regulate the resonant peaks. The CRCM presents a linear polarization conversion peak around 5.80 GHz, its polarization conversion ratio (PCR) is near 100%. The PCR is also larger than 80% from 5.56 GHz to 5.95 GHz. Through the surface current density distribution and the comparison between the CRCM and complementary-modeled double ring metamaterial (CDRM), the main factors generating polarization conversion are the asymmetry of metal pattern layer and magnetic resonance caused by reverse current. The CRCM also has two strong absorption peaks located at 6.31 and 9.37 GHz, respectively. Dielectric loss and ohmic loss are the main microwave loss mechanisms proved by volume and surface power loss density distribution. The resonant frequencies derived from [Formula: see text] resonant circuit are well consistent with the simulation data and measurement results.

Synthesis of Modulated Dielectric Metasurfaces for Precise Antenna Beamforming

This paper presents an end-to-end design method for the synthesis of dielectric metasurfaces with modulated thickness that are able to realize desired radiation patterns in the far field with high precision. The method relies on integral equations and the method of moments to calculate the induced surface and volumetric current densities throughout the metasurface upon a given incident illumination. By avoiding homogenization of the dielectric layer and calculating directly the scattered fields through the method of moments, the near-field and far-field response of the metasurface can be accurately predicted and optimized. In particular, a design example of a modulated dielectric metasurface, fed by a single embedded line source, is presented for the realization of a Chebyshev array pattern with $\ensuremath{-}20$-$\mathrm{dB}$ sidelobe level. Moreover, an externally fed dielectric metasurface performing beam splitting of a normally incident plane wave is designed, three-dimensionally printed and measured, showing two reflected beams at $\ifmmode\pm\else\textpm\fi{}{30}^{\ensuremath{\circ}}$, high suppression of specular reflections ($>14\phantom{\rule{0.2em}{0ex}}\mathrm{dB}$), and satisfactory agreement with the simulated and desired radiation patterns. The proposed design method for beamforming with dielectric metasurfaces can find application in higher frequencies where the use of copper may be problematic due to higher Ohmic losses and fabrication challenges.

On the ignition kernel formation and propagation: an experimental and modeling approach

The next generation of advanced combustion devices is being developed to operate under ultra-high-pressure conditions. However, under such extreme conditions, flame tends to become unstable and measurement of fundamental properties such as the laminar flame speed becomes challenging. One potential method to resolve this issue is measuring the ignition-affected region during spherically expanding flame experiments. The flame in this region is more resistant to perturbations and remains smooth due to the high stretch rates (i.e. small radii). Stable flame propagation allows for improved flame measurement, however, the experimentally observed kernel propagation is a function of both inflammation and ignition plasma. Therefore, the goal of the present study is to better understand the plasma formation and propagation during the ignition process, which would allow for reliable laminar flame speed measurements. To accomplish this goal, thermal plasma operating at high pressures is studied with emphasis on the spark energy effects on the formation of the ignition kernel. The thermal effect of the plasma is experimentally observed using a high-speed Schlieren imaging system. The energy dissipated within the plasma is measured with the use of voltage and current probes with a measurement of plasma sheath voltage drop as an input to numerical modeling. The measured kernel propagation rate is used to assess the accuracy of the model. The experiments and modeling are conducted in dry air at 1, 3, and 5 atm as well as in CH4-N2 mixtures at 1 atm, and kernel radius, temperature, and mass are reported. The voltage-drop (as a non-thermal loss) is measured to be approximately 330 5 V (dry air at 1 atm) for glow plasma with a large dependency on pressure, gas composition, electrode surface quality, electrode geometry, electrode shape, and current density. The same loss within the arc plasma is measured to be 15 5 V, however the arc phase loss which agrees with arc propagation is significantly higher (∼45 V) which suggest additional unaccounted for phenomena occurring during the arc phase. With these losses, the modeling results are shown to predict the final kernel radius within 10%–20% of the observed kernel size. The difference found between the modeling and experimental results is determined to be a result of assuming that the primary loss mechanism (voltage drop across sheath formation) remains constant for the duration of glow discharge. The discrepancy for arc discharge is discussed with several potential sources, however, additional studies are required to better understand how the arc formation affects the kernel propagation.

Design and Assessment of Bio-Inspired Antennas for Mobile Communication Systems

RF front-end system in the mobile communication system consists of an antenna, filter, and amplifier section. Now a day, there is a need to reduce the size of this RF front-end system. Here the challenge is the reduction in the size of the RF front end without degrading the performance. One way to reduce the size is by reducing the size or area of the antenna. This work proposes and simulates three Bio-inspired microstrip (BIMS) antenna designs. They are flower, Butterfly, and leaf shapes presented based on the perturbation method, Gielis super formula, and modified polar transformation models, respectively. These BIMS antennas were printed on fiberglass laminate (FR4) as substrate with a dielectric constant of εr = 4.4 and a loss tangent of 0.02. The simulation results cover parameters of the antenna, such as reflection coefficients (S11), surface current density (Jsurf), and radiation patterns. They offer a maximum gain of 14 dBi, 8 dBi, and 4dBi, respectively, and their results are compared with other works. These antennas are less in size, so they occupy less area compared to conventional rectangular or circular patch antenna, which radiates in L and S bands at different frequency ranges.

Switchable broadband/narrowband absorber based on a hybrid metasurface of graphene and metal structures.

This paper proposes a switchable broadband/narrowband absorber based on a hybrid metasurface comprising graphene and metal in the millimeter-wave regime. The designed absorber achieves broadband absorption when the surface resistivity of graphene Rs = 450 Ω/◻ and narrowband absorption when Rs = 1300 Ω/◻ and 2000 Ω/◻. The physical mechanism behind the graphene absorber is explored by analyzing the distributions of power loss, electric field, and surface current densities. An equivalent circuit model (ECM) based on transmission-line theory is derived to theoretically investigate the performance of the absorber, with ECM results in good agreement with simulation results. Furthermore, we fabricate a prototype and evaluate its reflectivity by applying various biasing voltages. The results obtained from the experiment are also consistent with those obtained from the simulation. When the external bias voltage is changed from +1.4 V to -3.2 V, the proposed absorber has an average reflectivity ranging from -5 dB to -33 dB. The proposed absorber has potential applications in radar cross-section (RCS) reduction, antenna design, electromagnetic interference (EMI) shielding, and EM camouflage techniques.

Electropolishing Stainless Steel Optimization Using Surface Quality, Dimensional Accuracy, and Electrical Consumption Criteria

Electropolishing (EP) processes require high electrical consumption that must be optimized to minimize production costs without sacrificing the objectives of surface quality and dimensional accuracy. The aim of the present paper was to analyze the effects of the interelectrode gap, initial surface roughness, electrolyte temperature, current density, and EP time on aspects of the EP process applied to AISI 316L stainless steel, which have not been examined in the literature, such as polishing rate, final surface roughness, dimensional accuracy, and electrical consumption cost. In addition, the paper aimed to obtain optimum individual and multi-objective considering criteria of surface quality, dimensional accuracy, and electrical consumption cost. The results showed that the electrode gap was not significant on the surface finish or current density, and the EP time was the parameter having the greatest effect on all criteria analyzed, with a temperature of 35 °C showing the best electrolyte performance. The initial surface texture with the lowest roughness Ra10 (0.5 ≤ Ra ≤ 0.8 μm) obtained the best results with a maximum polishing rate of ~90% and minimum final roughness (Ra) of ~0.035 μm. The response surface methodology showed the EP parameter effects and the optimum individual objective. The desirability function obtained the best global multi-objective optimum, while the overlapping contour plot provided optimum individual and simultaneous per polishing range.

Ultrathin Broadband Dual‐Ring Metamaterial Absorber Based on Chip Resistance

Herein, an ideal metamaterial absorber with broadband, ultrathin, and wide incidence angle is proposed. The absorption unit of the proposed metamaterial absorber consists of two double rings. And, eight chip resistors are loaded between them to increase the absorption bandwidth. It is showed in the simulation results that the structure absorbs more than 90% in the range of 8.6–17.4 GHz at vertical incidence. The total thickness of the absorber is 2.4 mm (0.069 λL), where λL is the lowest‐absorption frequency, smaller than the absorber structure of the same type of bandwidth. To understand the broadband absorption performance of this absorber, the effects of design parameters such as substrate thickness and resistive resistance are investigated. In addition, herein, to investigate the absorption mechanism of this absorber, the normalized impedance, electric field distribution, and surface current density are demonstrated. Finally, the absorber is fabricated and measured at vertical incidence, and the experimental results are in good agreement with the simulation results.

Inverse Source Solutions With Huygens’ Surface Conforming Distributed Directive Spherical Harmonics Expansions

Time-harmonic inverse source solutions are commonly working with electric and magnetic surface current densities defined and discretized on appropriately chosen Huygens’ surfaces. An efficient meshless alternative are spherical harmonics expansions of low-order distributed along the chosen Huygens’ surface, which still possess pretty good spatial localization properties. Similar to expansions with electric and magnetic surface current densities, distributed expansions with Cartesian spherical harmonics (SHCs) or standard vector spherical harmonics (SHVs) are redundant when they are placed on Huygens’ surfaces. This redundancy is reduced by allowing only spherical harmonics, which can be excited by surface current density distributions in a specific plane, and by forming directive spherical harmonics. This results in a considerable reduction of the necessary number of unknowns for representing the sources and improved conditioning of the discretized integral equations. Inspired by the Huygens’ radiator concept, appropriate directive harmonics on the basis of SHCs and SHVs are derived, implemented, and compared in terms of their performances. The validity of the presented techniques is confirmed via inverse source solutions for synthetic and real measurement data.

Modeling of a Rotary Actuator Using Elliptical Coordinates and Differential Flux Tubes

Analytical models are useful in the design of electromagnetic devices. In this article, a model is developed for a rotary actuator whose stator curvature is elliptically shaped to have a reluctance torque that restores the rotor to the maximum torque per ampere position. The total torque is decomposed into the coil torque and a reluctance torque. The rotor is a permanent magnet represented by equivalent Amperian currents. The stator geometry is simplified to an ellipse having surface current densities at the interpolar regions that are equivalent to the stator currents. Then, the field solution within the ellipse is obtained using Laplace’s equation in elliptical coordinates so that the coil torque can be obtained by the Lorentz force. The reluctance torque is derived by the energy method and an approach referred to here as differential flux tubes, which is similar to the use of conventional flux tubes in magnetic equivalent circuits. A rotating reference frame on the rotor is also adopted to simplify the mathematics. The finite element method (FEM) is also used in the field analysis and development of the proposed model. Finally, the actuator is prototyped, and experimental results are employed to evaluate the results obtained from the analytical model and FEM.

On electromagnetic impacts on the water absorption of vegetable seeds in the sown soil layer

One of the most important tasks for the agro-industrial complex of the Russian Federation is to develop methods for increasing crop seed viability. The way seeds absorb water determines the most important physicochemical processes that ensure their germination and further development of seedlings. There has been studied the impact of the magnetic field, direct and alternating current on the water absorption of cucumber and tomato seeds in the soil layer at a depth of 0.02 m. The surface current density was 0.0022 mA/cm 2, while the magnetic field induction was 3.1 mT. Within 5 hours with an interval of one hour, the seeds were removed and weighed. Direct current (negative/positive) has the greatest impact on the rate of water absorption of cucumber seeds, provided that the positive electrode is in the soil, while the negative one is on the soil surface (20.2% increase). The impact ranks second (12.7% increase), alternating current ranks third (10.1% increase). When using alternating current, the water absorption of tomato seeds increases by 80% higher, while using magnetic impact it increases by 50% than with no impact at all. There have been noted negative rates of water absorption. The results of the work can be used to develop the methods for controlling the rates of water absorption of vegetable seeds with the help of external electrophysical effects.

A new insight on the mechanisms of corrosion deactivation of a typical Ti/IrO2 + RuO2 +TiO2 coating in the presence of Ta2O5 in chlor-alkali medium

Mixed metal oxide (MMO) anodes are commonly used in chlor-alkaline industry. They have a longer lifetime than conventional graphite anodes due to the presence of valuable and expensive metal oxides such as iridium and ruthenium. However, they can suffer from pitting corrosion. This makes them to lose their stability, which necessitates the application of stabilizers to delay this process as one of the most accepted preventive measures. Hence, this study to aims to increase the life of MMO anodes, by altering corrosion mechanisms from localized to uniform corrosion. To achieve this objective, electrodes of different nominal compositions were prepared by adding 2 and 5 wt% of tantalum oxide into the base coating composition (Ti/(38IrO2-36RuO2-(26-X)TiO2-XTa2O5)). Accelerated lifetime and electrochemical impedance tests were employed in order to evaluate the corrosion pathways at different time intervals. Furthermore, morphological properties and composition of the anode were addressed via scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. In addition, cyclic voltammetry test was performed to investigate electrochemical properties. It was understood that the addition of tantalum oxide leads to increment in active surface area and current density of the anode reaction. More importantly, tantalum oxide was found to be an effective inhibitor of the pitting corrosion while altering the dominant corrosion pathway from pitting to uniform dissolution in ternary coatings. However, it resulted in the service life of the anode to be reduced in the accelerated life test.

NiO/Ni Heterojunction on N-Doped Hollow Carbon Sphere with Balanced Dielectric Loss for Efficient Microwave Absorption.

Hollow carbon spheres are potential candidates for lightweight microwave absorbers. However, the skin effect of pure carbon-based materials frequently induces a terrible impedance mismatching issue. Herein, small-sized NiO/Ni particles with heterojunctions on the N-doped hollow carbon spheres (NHCS@NiO/Ni) are constructed using SiO2 as a sacrificing template. The fabricated NHCS@NiO/Ni displayed excellent microwave absorbability with a minimum reflection loss of -44.04dB with the matching thickness of 2mm and a wider efficient absorption bandwidth of 4.38GHz with the thickness of 1.7mm, superior to most previously reported hollow absorbers. Experimental results demonstrated that the excellent microwave absorption property of the NHCS@NiO/Ni are attributed to balanced dielectric loss and optimized impedance matching characteristic due to the presence of NiO/Ni heterojunctions. Theoretical calculations suggested that the redistribution of charge at the interfaces and formation of dipoles induced by N dopants and defectsareresponsible for the enhanced conduction and polarization losses of NHCS@NiO/Ni. The simulations for the surface current and power loss densities reveal that the NHCS@NiO/Nihas-applicable attenuation ability toward microwave under the practical application scenario. This work paves an efficient way for the reasonable design of small-sized particles with well-defined heterojunctions on hollow nanostructures for high-efficiency microwave absorption.

Efficient Radiation Pattern Estimation of Slot Array Antennas Covered With Frequency Selective Surfaces Using Deterministic Ray Tracing

In this paper, we propose a novel algorithm to compute the radiation pattern of a slot array antenna covered with frequency selective surfaces (FSS) based on ray tracing technique. We observed that the proposed algorithm could greatly reduce computational resources while yielding accurate numerical solution, compared with cases taking standard full-wave and conventional high-frequency approaches (summarized in Table I). The underlying principle is to combine the image method and physical optics technique. More specifically, the proposed algorithm (i) employs a boundary box that encloses the slot array antenna with FSS to correct phase errors and then (ii) calculates equivalent surface currents flowing on the boundary box. The surface of the boundary box is discretized by regular grids (or boundary meshes) and a ray path reaching each square cell in the boundary meshes is determined based on the image method. After collecting all the rays hitting the boundary meshes, equivalent surface current densities can be computed for the resulting radiation pattern. The proposed algorithm is suited best for dealing with electrically large structures much more efficiently and can advance the existing design process.

Analytically Regularized Evaluation of the Coupling of Planar Concentric Conducting Rings

In this paper, an accurate and efficient method for the analysis of coupled perfectly conducting annular rings is presented. The problem is first formulated as a couple of Integral Equation (IEs) in the Vector Hankel Transform (VHT) domain, considered as unknowns in the cylindrical harmonics of the unknown surface current density. As a second step, Galerkin’s method is applied with suitable expansion functions. The selected functions have two main properties: they reconstruct the expected physical behavior of the nth cylindrical harmonic at the edges of the annular rings, and their VHT transform is analytical and can be expressed in closed-form. Consequently, the method is effective and the problem is regularized, as testified by the truncation error. Comparisons with the commercial software CST Microwave Studio have been carried out and are presented to validate the method.

Construction of the differential surface admittance operator with an extended Fokas method for electromagnetic scattering at polygonal objects with arbitrary material parameters

This article presents a novel method to accurately simulate electromagnetic scattering at homogeneous polygonal cylinders with arbitrary material properties. A single source equivalence approach is invoked, allowing to substitute the background medium for the inner material of the scatterer, provided an equivalent surface current density is introduced. We construct the pertinent differential surface admittance operator by means of the Fokas method, establishing a map between the known Dirichlet boundary values and their unknown Neumann counterparts. However, to allow for lossy materials, we extend the Fokas method to complex wavenumbers. The novel formalism, employing pulse-shaped local basis functions, natively supports combined magnetic and dielectric contrast, accurately captures the skin effect, and is conveniently integrated in traditional boundary integral equation formulations. The correctness and versatility of our technique are verified for various examples by means of analytical validation and through comparison with a Poggio-Miller-Chan-Harrington-Wu-Tsai approach, a volume integral equation method and a commercial solver.

Effects of Closed-Loop Devices on Omnidirectional Beam Patterns Radiated from WAVE Monopole Antennas

This study investigates the influence of closed-loop devices on omnidirectional beam patterns radiated from a Wireless Access for Vehicle Environment (WAVE) monopole antenna for facilitating communication stability in Vehicle-to-Vehicle and Vehicle-to-Everything technology. Single, dual, and quadruple closed-loop devices were introduced into the monopole antenna, and their surface current density and radiation beam patterns were analyzed by using the high-frequency structure simulator (HFSS) and computer simulation technology (CST) programs. As the closed-loop devices reflected the signal radiated from the antenna, the distribution of the surface current was concentrated around the monopole due to the creation of a closed-loop surface current path, which increased the gain value. The average gain was considerably increased by introducing closed-loop devices. The proposed antenna has an average gain of 1.57 dBi and a peak gain of 6.29 dBi at the operating frequency. Furthermore, omnidirectional beam patterns with a beam width of 359° were obtained by introducing four closed-loop devices into the monopole antenna, which eliminated nearly all null points in the frequency range of 5.85–5.925 GHz.

Nanoparticle Shape Optimization for Tamm-Plasmon-Polariton-Based Organic Solar Cells in the Visible Spectral Range

The effect of the shape of the nanoparticles and the polarization of incident light on the surface current density and the efficiency of an organic solar cell based on the Tamm plasmon polariton is investigated. In the cases of both elongated and flattened nanoparticles, it is shown that the efficiency of such a solar cell is increased when the electric field vector is parallel to the largest axis of the spheroid.

Electric current paths in a Si:P delta-doped device imaged by nitrogen-vacancy diamond magnetic microscopy

The recently-developed ability to control phosphorous-doping of silicon at an atomic level using scanning tunneling microscopy, a technique known as atomic precision advanced manufacturing (APAM), has allowed us to tailor electronic devices with atomic precision, and thus has emerged as a way to explore new possibilities in Si electronics. In these applications, critical questions include where current flow is actually occurring in or near APAM structures as well as whether leakage currents are present. In general, detection and mapping of current flow in APAM structures are valuable diagnostic tools to obtain reliable devices in digital-enhanced applications. In this paper, we used nitrogen-vacancy (NV) centers in diamond for wide-field magnetic imaging (with a few-mm field of view and micron-scale resolution) of magnetic fields from surface currents flowing in an APAM test device made of a P delta-doped layer on a Si substrate, a standard APAM witness material. We integrated a diamond having a surface NV ensemble with the device (patterned in two parallel mm-sized ribbons), then mapped the magnetic field from the DC current injected in the APAM device in a home-built NV wide-field microscope. The 2D magnetic field maps were used to reconstruct the surface current densities, allowing us to obtain information on current paths, device failures such as choke points where current flow is impeded, and current leakages outside the APAM-defined P-doped regions. Analysis on the current density reconstructed map showed a projected sensitivity of ∼0.03 A m−1, corresponding to a smallest-detectable current in the 200 μm wide APAM ribbon of ∼6 μA. These results demonstrate the failure analysis capability of NV wide-field magnetometry for APAM materials, opening the possibility to investigate other cutting-edge microelectronic devices.