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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.