Search

This paper deals with the diffusion of rotating electromagnetic fields into hysteretic materials. A simplified vector formulation based on a parallelogram hysteresis model has been investigated, in order to significantly reduce the computational effort. Vector saturation and loss properties are discussed. The whole simulation has been done by the use of a finite-element time-domain algorithm. Index Terms--Finite-element method (FEM) simulation, parallelogram model, vector hysteresis.

This paper introduces a simplified vector model based on the Preisach approach that intrinsically satisfies loss and saturation properties. It is able to reproduce isotropic and nonisotropic behavior. The main idea is to compute the magnetization vector in two steps independently, amplitude and phase. The first one is computed by means of a scalar Preisach model with a distribution depending on the angle of the applied field with respect to a fixed direction. The phase is computed by means of a phase diagram and a simple function that take into account the history of the angle between magnetization and applied field. The proposed formulation allows fast computation of rotational and alternative vector magnetization, the computational time is of the order of two times the scalar Preisach model. Index Terms--Magnetic materials, Preisach model, vector hysteresis.

This paper discusses the numerical implementation of a new vector hysteresis model, the radial vector model, introduced as general hysteresis vector model for both isotropic and anisotropic magnetic materials. The present implementation is a 2-D one that uses ellipses as critical surfaces. The results computed by the model, applied to some basic vector hysteresis configurations, are in agreement with experimental behavior. Index Terms--Hysteron critical surfaces, magnetic vector hysteresis, modeling.

This paper deals with the characterization of dynamic loops shapes and losses in soft magnetic materials. An experimental and theoretical analysis has been done in order to describe static and dynamic hysteresis on soft ferrite cores. A parallelogram-loop-based hysteresis modeling is described and discussed. The possibility of the model to include vector hysteresis and the related properties are then discussed, with particular attention to the case of a rotating magnetic field into an isotropic and anisotropic medium. Index Terms--Dynamic modeling, magnetic hysteresis, soft materials, vector modeling.

In this paper, we present and discuss the use of a reduced Preisach vector model (RVPM) as a numerical tool for the analysis of the influence of the cut angle in the magnetic behavior of laminated Fe-Si steels. The model parameters can be deduced by measurements along the easy and hard axis, and the families of hysteresis loops and virgin curves for the same Si-Fe sheet, cut at different angles with respect to the rolling direction can be derived. In particular, we present a simplified identification procedure based on the assumption that the material is single-quadrant medium along the principal axes. Results seem to indicate that the hypothesis of factorizable Preisach function is not compatible with the real magnetic materials. Index Terms--Hysteresis, modeling, vector processing.

The characterization of the energetic magnetic behavior of hysteretic materials and the determination of the surface impedances are proposed. A numerical model in time domain is adopted for the calculations. The use of parallelogram-shaped hysteresis loops allows for simplifying the numerical formulation and for reducing the computation time with respect to more accurate models. Equivalent major loops have been defined starting from the measured ones. Comparison with the modified scalar Preisach model is presented and discussed. Index Terms--Finite-difference time domain (FDTD), magnetic hysteresis modeling, surface impedance.

In this paper we discuss the electro-thermal behavior of solid armatures in railguns. This discussion is based on a review of results obtained by a theory that takes into account the three-dimensional nature of melting and vaporizing of the contact surface between rail and armature. This theory is numerically treated by an integral approach based on a suitable decomposition of rails and armature in hexahedrons, bricks and filamentary elements. After a recall of the main points of this theory and the related numerical technique, this review paper describes the principal features about the current flow, the heat production and exchange, the presence of liquid and vapor phases at the contact face of the armature, derived by this theory. ln particular the shape of the melt front and the critical transition velocity predicted are in agreement with the experimental observations. Index Terms - Integral equations, Railguns, Skin effect, Transition metal materials.

In this paper the efficiency of equipotential and grounding systems with respect to an electrostatic discharge (ESD) event is investigated. This investigation has been made from a numerical point of view by a suitable application of Finite-Difference in Time-Domain (FDTD) algorithms to analyze different grounding system configurations, and by an experimental point of view by carrying out a measurement system for the conducted interferences in metallic objects connected to ground and stroked by ESD. Experimental measurements have been used here to validate the numerical procedure. Index terms - Electrostatic discharges, Grounding, FDTD Methods, Measurement.

This paper deals with a complete three-dimensional calculation of the magnetic vector potential and of the magnetic flux density created by disk conductors, in which an assigned current flows. The formulas presented are valid either inside or outside the conductor. The effectiveness and the time-saving possibilities of the expressions derived is shown by comparison with the numerical results obtained by direct integration of the Biot-Savart formulas and with experimental results. Index terms - Magnetic fields, integral equations, algorithms.

In this paper a numerical model for the computation of the electromagnetic field produced by an electrostatic discharge (ESD), occurring in the vicinity of a system of conducting objects, is presented. The ESD is modeled by a current flowing into a ionized channel located between two initially charged surfaces. The electromagnetic field generated by the ESD event is computed by means of a finite-difference time-domain (FDTD) algorithm based on the Yee's space-time mesh, and on the Mur's absorbing boundary conditions (ABC). A validation of the model by comparison against measured data is shown and an application to the analysis of the electromagnetic (EM) field produced by an ESD in a shielded box is presented.

In this paper an approach to the numerical analysis of the electromagnetic interferences (EMI) radiated by metallic grids, like Faraday's cages, hit by a lightning stroke is proposed. This approach is based on a hybrid differential-integral mathematical formulation in which a Finite-Difference Time-Domain scheme is used to evaluate the current density distribution inside the conductors, while the Kirchhoff's integral expressions are used for the computation of the transient electric and magnetic fields generated by the current flow into the grid. The introduction of a suitable scalar potential defined on the surface of the conductor allows to determine a complete set of boundary conditions for the problem of the magnetic diffusion of the current into the conductor and to reduce the region to be numerically treated by the differential formulation to the only conducting materials. Examples of application of the method to the numerical analysis of the EMI radiated by a Faraday's cage struck by lightning are given.

This paper deals with the numerical analysis of the behavior of diffracting perforated shields, and in particular of honeycomb structures. For the numerical computation a Yee's finite difference algorithm with Mur's absorbing boundary conditions is employed. A particular technique allows to limit the spatial dimension of the simulating grid, suitably taking into account the external field source. The computed results show the effectiveness and the accuracy of the method.

In this paper, the problem of the electromagnetic diffusion of electrostatic discharge (ESD) currents, interfering directly on the metallic enclosures of electronic equipments, and of the electromagnetic interferences (EMI) produced, is modeled and computed via a suitable finite-difference time-domain numerical approach. The levels of the radiated fields produced by standard ESD current waveforms in grounded metallic shells are evaluated, and the effects of the different arrangements of the grounding wires of the enclosure on the resulting EMI levels are discussed.

This paper deals with a numerical modelling of the interferences produced by electrostatic discharges that reach the surface of metallic boxes containing electronic circuits and flow toward the ground connections. The wave-form of the interfering current assumed is taken from the draft of the CENELEC ESD Standard. The distribution of the current density into the enclosure during the electrostatic discharge event is deduced by means of a scalar magnetic potential approach in the frequency domain, and by a consequent finite difference discretization. The passages from the frequency domain to the time domain and forward are made using the discrete Fourier transform. This formulation of the problem allows the simulation grid to be reduced to only the metallic enclosure, saving time either in preparation of the input data or in the numerical computation. The electromagnetic interferences radiated by the enclosure during the electrostatic discharge event are directly computed by multipole expansion of the resulting current density distribution.