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This paper revisits the problem of shielding low-frequency high magnetic fields. Such fields are encountered in the domain of electromechanical energy conversion particularly during railgun operation. Using finite-element analysis, we investigate, separately, the mechanism of redirection of the magnetic flux due to induced eddy currents and the magnetic flux shunting due to highly permeable materials. In a first phase, various shapes of highly conductive shields are analyzed in the frequency domain. In a second phase, we study the shunt effect of different shields being made of magnetic materials. In a magnetostatic model afterward, for a shield that combines both highly conductive and magnetically highly permeable materials, the case of a double-exponential-shaped magnetic field is treated in the time domain. Finally, we make some remarks on the concept of shielding effectiveness. Index Terms--High magnetic field, low frequency, magnetic shielding, shielding effectiveness (SE).

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 considers the design of a plasma electromagnetic launcher aimed at determining the gyroscopic stabilization of the launch mass. The basic idea is to provide the rotation to the projectile during its acceleration inside the bore by means of a rotating magnetic field. In order to create the rotating field, a three-phase winding coil system is adopted. The design procedure of the main elements (the rails, the coil system, and the projectile) of the electromagnetic device is described in detail. The results obtained for the specific ease of a launch mass of about 8 kg with outgoing velocity of 2 km/s are reported and discussed. Index Terms--Gyroscopic stabilization, plasma electromagnetic launcher, prototype design.

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.

This paper proposes a new way to measure the shielding effectiveness of ferromagnetic shields. The procedure combines an experimental characterization of the shielding material and numerical simulations. In a first case, magnetic hysteresis is reduced to a series of equivalent B-H linear relations through an optimization procedure that is applied to a measured set of symmetric minor loops, and an equivalent multilayer linear medium is defined through a subsequent iterative procedure. In a second case, magnetic hysteresis is reduced to a simple B-H nonlinear relation, obtaining an equivalent nonlinear shield. In both cases, the obtained results are compared with the direct measurements of the shielding effectiveness at different operating frequencies, showing good agreement and the validity of the proposed method. A comparison and a discussion on the harmonic content of the attenuated field for the investigated shield geometry are reported. The same analysis is carried out for a basic diffusion problem, comparing the results with those obtained by the use of a Preisach model. [ABSTRACT FROM AUTHOR]

Defines a stable finite difference discretization for problems of electromagnetic field diffusion in non-linear hysteretic media. Discussion on finite difference implicit time-domain algorithm and stability analysis; Numerical results.

Presents a numerical procedure capable of analyzing a nonlinear diffusion of an electromagnetic field into a hysteretic magnetic conductor half-space. Evaluation of surface impedance of hysteretic materials; Formulation of nonlinear impedance boundary conditions; Description of hysteretic behavior through a modified scalar Preisach model.