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The electromagnetic interaction between a circular disk with finite conductivity and finite thickness and a coaxial circular loop of constant current is addressed here. The finite conductivity and thickness of the material disk lead to the adoption of suitable generalized boundary conditions, and the problem is thereby reduced to the solution of two sets of dual integral equations in the Hankel transform domain. Such equations are then solved by expanding the spectral unknowns in Neumann series of Bessel functions. An alternative formulation that is valid for purely conductive screens with no magnetic properties, which is computationally much faster, is proposed as well. The magnetic shielding effectiveness of the structure is studied in detail, pointing out its dependencies and possible critical situations. [ABSTRACT FROM AUTHOR]

In turn, this requires the ability to clear overhead line faults, either by means of circuit breakers tailored for HVDC applications, providing adequate breaking current ratings at line voltage [[2]], or by adopting converter topologies intrinsically able to interrupt DC fault currents [[3]], i.e., full-bridge or similar. In [[11]], a different DC breaker architecture based on the superconductive elements' double quench is modeled in the software PSCAD/EMTDC, and the fault current interruption is analyzed for two scenarios, i.e., "larger" and "lower" fault current values. Multiterminal DC (MTDC) systems fault analysis and protection is discussed in several papers, either from the perspective of the system or of its components (i.e., DC breakers) [[5]]. Lacking operational DC circuit breakers, DC cables are the only option for HVDC-VSC transmission, but in some cases, cables might be preferred to overhead lines due to their reduced environmental impact and the rather intricate authorization processes which discourage the realization of new overhead power lines. [Extracted from the article]

The magnetic shielding effectiveness of a single planar screen of infinite extent against a parallel current loop source is evaluated through an analytic closed-form expression which is valid for arbitrarily thick screens and for any source-observation distance. The only assumption in the formulation consists in considering small loops having a constant current. The resulting formula can be expressed in terms of only elementary functions and is believed to represent the most general closed-form expression for the magnetic shielding effectiveness of a planar screen in the presence of a parallel loop. Numerical results are provided to show the generality and the validity of the proposed formula. [ABSTRACT FROM AUTHOR]

The field penetration through a circular aperture in an infinite plane with a nonzero surface impedance excited by an axially symmetric source is analytically investigated. The problem is formulated in terms of an original dual-integral-equation approach and solved through the method of moments in the Hankel spectral domain. The proposed formulation is applied to the calculation of the axial magnetic field when the source is a current loop of finite radius coaxial with the aperture and it is shown that it is possible to separate the contributions of the aperture and of the nonzero impedance plate to the transmitted field. In the case of low frequencies and small apertures, closed-form expressions are also derived. Moreover, the approach is also applied to the case of a perfectly conducting plane giving rise to results that coincide with those recently presented in the literature. Finally, the accuracy of the proposed approach is validated through full-wave calculations. [ABSTRACT FROM AUTHOR]

Day-ahead PV production forecasting can be crucial not only for energy allocation in the day-ahead market, allowing the direct participation in markets of PV power plants and aggregated systems, but also for predictive maintenance. This means that if the correlation between environmental factors and PV degradation rates is known, these can be estimated for any location worldwide, even before PV systems are operational. The number of field data to analyze increases as PV systems become larger, making manual PV monitoring more and more challenging. In [[20]], the authors use long short-term (LSTM) neural networks on a multivariate set of input data: they use publicly available weather reports and measured PV power output. [Extracted from the article]

The shielding performance of a planar metamaterial wire-medium (WM) screen under plane-wave illumination is studied. The screen consists of a finite number of periodic layers of thin conducting cylinders embedded in a dielectric matrix; in the low-frequency limit and for waves with the electric field polarized along the wire direction, such a screen can be modeled as a homogeneous slab with a plasma-like dispersive permittivity. In particular, well below the plasma frequency, the effective relative permittivity is negative and very large in absolute value, giving rise to high values of the shielding effectiveness. A comparison with a conventional planar metal screen is reported, showing how the proposed structure can be designed to be advantageous in terms of low density and weight saving. In order to be effective against arbitrarily polarized waves, the original structure is modified, adding a second WM screen with wires orthogonally oriented with respect to the first one. Numerical results are provided that illustrate the validity of the homogenized model in predicting field levels both near to and far from the screen and show the shielding performance attainable with the proposed metamaterial screen in both single- and double-layer configurations at normal incidence. Index Terms--Artificial materials, electromagnetic screen, metamaterials, shielding effectiveness (SE), wire medium (WM).

The aim of this work is to design an innovative exposure system that enables accurate reproduction of various high-frequency exposure environments for the experiments. Attention is given to the solution of the general problem concerning the design of an antenna system, given a set of constraints on the field components profiles. Special reference is made to the replication of the field distribution due to radio base (RB) stations for mobile communications, but the procedure may be applied to other sources as well, without significant modifications. The sources adopted for this purpose are microstrip antennas. The field profiles obtained by means of the realized source system have been measured and compared favorably with the design specifications. The root means square (rms) value and the polarization and spatial variations are replicated. Index Terms--Biological effect, method of moments (MoM), microstrip antenna, radio base (RB) station.

This paper describes a versatile exposure system for the reproduction of static and extremely low-frequency (ELF) magnetic fields. The system can be used for in vitro and in vivo experiments. The exposure setup consists of six circular loops, each placed on the face of a cubical box and suitably fed. The paper shows, by means of a genetic-algorithm approach to optimize the degrees of freedom of the system, that such a configuration allows a given magnetic field to be reproduced, with great accuracy, in amplitude, phase, and polarization, on a specific surface of interest. The paper provides details of the design procedure and presents extensive numerical simulations that confirm the validity of the proposed design procedure. Index Terms--ELF magnetic fields, exposure systems, genetic algorithms, loop antennas, static magnetic fields.

A novel wavelet-based technique is presented for the extraction of two-port equivalents of common printed circuit board (PCB) discontinuities. The wavelet-transformed scattering parameters of the discontinuity can be included in a wavelet equivalent of TEM wave propagation paths along the PCB in order to obtain an overall equivalent of the whole structure under analysis. The wavelet representation minimizes the CPU time and computer storage requirements while maintaining excellent accuracy, thus, it proves to be a very useful modeling tool, especially in the design stage. Index Terms--Multiresolution analysis, printed circuits, wavelet transforms.

We present a method for the analysis of ferromagnetic shields under low-frequency excitation conditions and demonstrate its validity. The source types are arbitrarily oriented current loops or multiconductor lines. We account for hysteresis by means of the Jiles-Atherton model and solve the relevant equations in the time domain by adopting a finite-element time-domain procedure. Index Terms--Ferromagnetic materials, finite-element methods, hysteresis, magnetic shielding, power cables.

The analysis of shielding performance of planar shields against near field sources is carried out in the time domain to account for the nonlinear behavior of ferromagnetic materials used in low frequency applications. To this end, the Schelkunoff approach for shielding problems has been reformulated in the time domain introducing the transient wave impedances which relates transient electric and magnetic field components and appear in the integrodifferential boundary conditions. The final equation system is solved by means of a numerical procedure based on the Finite Element Method. The obtained results are compared with analytical and measured data in different configurations.

A new FE-based approach is proposed for the analysis of the EM field distribution inside enclosures with conducting walls which can be penetrable at some frequencies. Equivalent electric- (magnetic-) field source-distributions and equivalent wave impedances (admittances) are applied on the inner metallic edges of the structure, in analogy with the Thevenin (Norton) approach, in order to predict the effects of an incident TE- (TM-) polarized plane wave. Applications are carried out to assess the efficiency and accuracy of the method, considering different 2D-configurations.

In the low-frequency (LF) range ferromagnetic materials are often used to shield sensitive apparatus and systems from external electromagnetic (EM) fields; because of their nonlinear behavior a time domain analysis is required. The FE-TD method is applied to the plane wave shielding analysis of commonly-used planar shield configurations, improving the efficiency of standard algorithms. Normal and oblique incidence are considered.

Analytical solution of lossless field-excited multiconductor transmission lines is presented. The equivalent circuit of a multiconductor transmission line with distributed sources is reduced to a simple lumped parameter circuit with independent voltage sources at both the ends of the transmission line. The transient source waveforms are analytically estimated for exponential time dependence of the external field, as EMP, ESD, and lightning. The method is suitable for a direct implementation in computer-aided circuit analysis codes and enables a very fast analysis for any load condition. Some numerical results are presented for single conductor and multiconductor lines excited by an EMP plane-wave field.

A time-domain finite-element based algorithm is presented to evaluate the voltage and current wave propagation in lossy multiconductor lines. The integrodifferential equations take into account exactly the skin and proximity effects in the time domain. An automatic criterion for the choice of the optima time stepping is adopted in order to reduce the computer runtime. A valuable reduction of the number of time steps is achieved with no loss of accuracy with respect to a constant discretization.

The transmission of an electromagnetic field produced by a current loop of finite radius through a coaxial circular aperture in a perfectly conducting plate is evaluated through a rapidly convergent formulation in an exact form. By applying the equivalence principle, the problem is first formulated in the Hankel transform domain, obtaining a set of dual integral equations in which the equivalent surface magnetic current density defined on the aperture is not known. The set of dual integral equations is regularised in a second‐kind Fredholm integral equation by applying the Abel integral‐transform technique. The solution is achieved by expanding the unknown in a set of orthogonal basis functions that correctly reproduce the behaviour of the equivalent magnetic current at the edge of the aperture. Finally, under particular assumptions, a low‐frequency solution is extracted in a closed form. Numerical results are reported to validate the accuracy and efficiency of the proposed formulations. [ABSTRACT FROM AUTHOR]

In this article, the low-frequency magnetic shielding effectiveness of a planar screen with magnetic and conductive properties in a coplanar-loops configuration (as required in the IEEE Standard 299) is evaluated through a new closed-form formula under the thin-sheet and small-loop approximations. The formulation clearly shows the separate contribution of the permeability and the conductivity of the screen to the shielding performance. The results obtained with the proposed closed-form formulas are compared with the exact ones derived through numerical integrations to assess the relevant accuracy and limits of validity. [ABSTRACT FROM AUTHOR]

This article shows the advantages provided by implicit time stepping schemes for the study of multiconductor transmission lines. Implicit schemes allow for choosing time and space steps independently by attending only to resolution criteria, without the limitation imposed by the Courant–Friedrich–Levy stability condition. Hence, they behave favorably whenever a large time step would be preferable, for instance when a massive number of simulations is required for sensitivity analyses. We focus our attention on two common schemes in electromagnetics, Crank-Nicolson and Newmark-β methods, that are shown to have the same accuracy and to lead to the same solving-equation structure. We illustrate how to include frequency-dependent losses in the algorithms, and we show the influence of dispersion on fast transients. Results show that implicit formulations can be favorably compared with the classical explicit leap-frog scheme. [ABSTRACT FROM AUTHOR]

A recent analytical formulation for the low-frequency magnetic shielding effectiveness of a thin metal screen against a circular loop source is extended to the case of a screen exhibiting both magnetic and conductive properties. The presence of magnetic properties introduces a series impedance in the equivalent network of the structure, in addition to the shunt admittance associated with the screen conductivity. However, the fields scattered by the two elements do not interact and hence can be treated independently; furthermore, the series impedance gives rise to integrals akin to those stemming from the shunt admittance. A generalized analytical formulation for a combined magnetic and conductive screen is thus obtained, that is favorably compared with both classical approximate formulations and exact results. [ABSTRACT FROM AUTHOR]

The magnetic shielding effectiveness of a planar metallic screen of infinite extent against a circular loop field source is analytically evaluated in a new closed-form formula under the thin sheet and small-loop approximations. The results obtained with the proposed formulation are compared with the exact ones derived numerically and with those obtained through classical approximate formulations. It is thus shown that the proposed formula is the most accurate closed-form expression proposed so far and the frequency range where a percentage relative error less than $\text{1}\%$ is obtained is clearly identified. [ABSTRACT FROM AUTHOR]

The improvement of the lightning performance of overhead distribution lines, hit by direct strokes, is investigated considering the use of additional shield wires beneath the phase conductors. The frequency-domain theory of multiconductor transmission lines with periodical grounding is adopted permitting a rigorous evaluation of the phase and shield wire currents and of the overvoltages across insulators. These can be minimized by careful positioning of the underbuilt shield wires. A sensitivity analysis on the overvoltages is conducted by varying either the position of the underbuilt shield wires and the grounding impedance. [ABSTRACT FROM AUTHOR]

The problem of radiation of a magnetic dipole axially symmetric with an infinitesimally thin perfectly conducting circular disk is solved in an exact closed form. This is done by transforming the original dual integral equation system describing the problem into a single second-kind Fredholm integral equation and searching for the solution as a power series. Both low- and high-frequency asymptotic limits are also discussed from which simple approximate solutions are readily derived. Numerical results are provided to validate the proposed formulation. [ABSTRACT FROM AUTHOR]

The electromagnetic problem of calculating the pulsed radiation from a horizontal magnetic dipole in the presence of a planar thin conductive screen is solved analytically in the time domain via a modified Cagniard-de Hoop approach. The components of the relevant time-domain electric and magnetic dyadic Green's functions are expressed by simple one-dimensional integrals over a finite integration domain. Expressions for the transient electromagnetic fields can thus easily be obtained and numerical results are provided that illustrate the main time-domain shielding characteristics. [ABSTRACT FROM AUTHOR]

The problem of evaluating the shielding effectiveness of a thin metallic circular disk with finite conductivity against an axially symmetric vertical magnetic dipole is addressed. First, the thin metallic disk is modeled through an appropriate boundary condition, and then, as for the perfectly conducting counterpart, the problem is reduced to a set of dual integral equations which are solved in an exact form through the application of the Galerkin method in the Hankel transform domain. A second-kind Fredholm infinite matrix-operator equation is obtained by selecting a suitable set of basis functions. A low-frequency solution is finally extracted in a closed form. Through a comparison with results obtained from a full-wave commercial software, it is shown that such a simple approximate solution is accurate up to the frequency where the surface-impedance model of the thin disk is valid. [ABSTRACT FROM AUTHOR]

The problem of the shielding evaluation of an infinitesimally thin perfectly conducting circular disk against a vertical magnetic dipole is here addressed. The problem is reduced to a set of dual integral equations and solved in an exact form through the application of the Galerkin method in the Hankel transform domain. It is shown that a second-kind Fredholm infinite matrix-operator equation can be obtained by selecting a complete set of orthogonal eigenfunctions of the static part of the integral operator as expansion basis. A static solution is finally extracted in a closed form which is shown to be accurate up to remarkably high frequencies. [ABSTRACT FROM AUTHOR]

The three-dimensional potential time-domain Green's function for a vertical electric dipole radiating in vacuum in the presence of a graphene sheet is derived in a semi-analytical form, by assuming a local Drude-like model for the graphene conductivity in the intraband regime, through a modified Cagniard-de Hoop approach. The derived expression is simple and requires only a straightforward evaluation of a finite smooth one-dimensional integral. Moreover, for the particular and practical case of source and observer along the same vertical axis, the result is provided in a closed form thus allowing for an extremely efficient calculation of the pulsed time-domain field. Numerical results are provided that validate the proposed formulation and assess its computational efficiency against a direct numerical inversion of the relevant spectral-domain potential. [ABSTRACT FROM AUTHOR]

The dispersive properties of the first higher order (EH $_1$ ) mode in uniform graphene nanoribbons over a ground plane are numerically studied to point out the characteristics of the bound-mode and leaky-mode regimes. The graphene nanoribbon is then suitably designed to operate on the EH $_1$ mode as a frequency-scannable leaky-wave antenna in both the millimeter and terahertz ranges. [ABSTRACT FROM AUTHOR]

The classical problem represented by a planar thin conductive shield in the presence of vertical dipole field sources (electric or magnetic) is solved analytically in the time domain via the Cagniard-de Hoop technique. Comparisons with numerical solutions carried out by means of efficient integration algorithms are provided and discussed. [ABSTRACT FROM AUTHOR]

The 3-D time-domain Green’s function (GF) for the vector potential excited by a transient vertical electric dipole in the presence of a thin sheet with high-contrast dielectric and conductive properties is derived using a modified Cagniard–de Hoop approach. The resulting expression involves the numerical evaluation of a 2-D integral over a finite integration domain, computationally much less expensive than the direct numerical evaluation of the inverse Laplace/Hankel transform of the relevant spectral-domain GF. Expressions for the transient electromagnetic fields can thus be obtained, and numerical results are provided, which illustrate their salient features and validate the proposed formulation. [ABSTRACT FROM AUTHOR]

The twenty-four papers in this special section focus on electromagnetic shielding and absorbers. [ABSTRACT FROM AUTHOR]

In high-voltage transmission lines, the continuity of shield wires is often broken to reduce losses. The accurate simulation of the effects of this practice on power line communications in multiconductor transmission lines is performed in order to put in evidence the relevant channel features and the consequences on the radiated electromagnetic fields. [ABSTRACT FROM PUBLISHER]

During transients involving multiconductor lines, the importance of the ground finite conductivity is well known and various techniques and expressions have been presented in literature for the inclusion of its contribution into the per unit length parameters. The direct time domain approach based on the introduction of the transient parameters and on the numerical solution of the telegrapher's equations demonstrated to be accurate and efficient for the analysis of typical transients. In this letter, the expressions for the ground transient resistance for underground cables, based on the closed-form inverse Laplace transform of the classical Pollaczek expressions (valid for the low-frequency-range), are presented and discussed. [ABSTRACT FROM AUTHOR]

ZnO is receiving a considerable attention for the development of novel cost-effective nanostructures with outstanding functional properties for applications in electronics and energy. In this paper, we investigate the effects of the nonlinear piezoelectricity, that has been recently observed in ZnO nanostructures, on the piezotronic effect of ZnO nanowires (NWs). We insert a physically-based model of the nonlinear direct piezoelectric effect into a fully-coupled thermo-mechanical-electric scheme to study the current–voltage characteristic of ZnO NWs under a purely vertical compressive/tensile strain. Our results show for the first time that the nonlinear piezoelectricity deeply affects the current transport processes inside the NW and the behavior of devices for piezoelectric-piezotronic applications and provides remarkable insights into the underlying physics. [ABSTRACT FROM PUBLISHER]

The analysis of the shielding performance is conducted on the basis of the classical IEEE Standard 299, which is typically a local and frequency-domain approach, may be not sufficient for the thorough appraisal of protection levels achievable through actual enclosures in the presence of transient electromagnetic fields. Stemming from a victim point of view, a new, global approach is proposed for the assessment of average and minimum guaranteed shielding performance directly in the time domain, in the presence of either near fields or plane waves. The method is suitable for the analysis of all the typical transient EMI phenomena and recommended for the analysis of protection levels of mission-critical devices or systems. An elementary statistical analysis of performance data is also presented. [ABSTRACT FROM PUBLISHER]

Grounding systems (GSs) must be tested periodically in order to maintain the touch voltage (TV) and step voltage (SV) below a safe value in all of the zones of the installation. Measurements of the ground resistance and of the TV and SV are typically done by the fall-of-potential (FoP) method, locating the auxiliary current electrode at remote distance to test the effective behavior of the GS. In urban areas, it could be very complicated or impossible to install the auxiliary current electrode as required, not having area around with sufficient accessibility. At this aim, this paper describes a methodology of using multiple current electrodes at short distances, modifying the classic FoP practice, so that the measurements of TV and SV are always conservative. The adequacy of a GS is verified if the values of the TV and SV, tested inside and in the vicinity of the GS, are below the permissible limits, regardless if they are true or conservatively increased. Thus, the measured TV and SV by the suggested method, always conservative, allow verifying the adequacy of GSs, in the cases where it is impossible to locate the remote auxiliary electrode. [ABSTRACT FROM AUTHOR]

The shielding performance of different buildings in presence of indirect lightning return strokes are investigated directly in the time domain. To this end, a sensitivity analysis is conducted by varying the channel geometrical characteristics and considering three different buildings. The performance is evaluated by adopting the time-domain shielding parameters recently proposed, which appear to be suitable for shielding studies in presence of lightning electromagnetic pulses. The results confirm the usefulness of introducing different parameters to fully characterize the shielding behavior of buildings exposed to lightning electromagnetic fields. [ABSTRACT FROM PUBLISHER]