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An advanced magnetic hysteresis modelling, exploiting the Preisach theory and the neural networks, is applied and discussed for the simulation of the magnetization processes of magnetic components made by laser powder bed fusion. Silicon iron samples with different percentage silicon content are used for the evaluation of the accuracy and reliability of the proposed approach. Measurements of the hysteresis loops and energy losses are compared with the computed results for different magnetization amplitudes and frequency rates. This approach is presented and evaluated here to provide a method for the accurate representation of the magnetization processes and the prediction of energy losses involved in additively manufactured ferromagnetic cores, in order to optimize their energy efficiency along different applications.

Rotational magnetizations of an Ni-Fe alloy are simulated using two different computer modeling approaches, physical and phenomenological. The first one is a model defined using a single hysteron operator based on the Stoner and Wohlfarth theory and the second one is a model based on a suitable system of neural networks. The models are identified and validated using experimental data, and, finally, an example of their application for a finite-element analysis is given.

A moving approach for the VHM (Vector Hysteron Model) is here described, to reconstruct both scalar and rotational magnetization of electrical steels with weak anisotropy, such as the non oriented grain Silicon steel. The hysterons distribution is postulated to be function of the magnetization state of the material, in order to overcome the practical limitation of the congruency property of the standard VHM approach. By using this formulation and a suitable accommodation procedure, the results obtained indicate that the model is accurate, in particular in reproducing the experimental behavior approaching to the saturation region, allowing a real improvement respect to the previous approach.

In this paper, we propose a dynamic model of the electrical transformer suitable for the numerical prediction of the inrush currents due to the arbitrary initial excitation of a transformer after a switch-OFF. In particular, the proposed model can be helpful to control strategies to avoid a transient current overshoot, based on the prediction of the residual magnetic flux.

A new general typology of optimization algorithm inspired to classical swarm intelligence, the Continuous Flock-Of-Starlings Optimization (CFSO), is used to face the inverse problem of modeling magnetic materials. It is obtained by translating the numerical swarm/flock-based algorithms into differential equations in the time domain and employing analytical closed-forms written in the continuum. The modeling of magnetic hysteresis is very important for the development of magnetic materials and the accurate design of electrical machines. Recently several hysteresis vector models have been proposed and discussed; one of them is the Vector Hysteron Model (VHM) which is a natural extension of the Preisach theory to the vector case. In this work we present a CFSO based approach for the identification of VHM in order to reproduce scalar and rotational hysteresis loops. Experimental validations are made for both NOG (Not oriented grain) and OG (Oriented grain) steels.

A new hysteresis operator for the simulation of Goss-textured ferromagnets is here defined. The operator is derived from the classic Stoner–Wohlfarth model, where the anisotropy energy is assumed to be cubic instead of uniaxial, in order to reproduce the magnetic behavior of Goss textured ferromagnetic materials, such as grain-oriented Fe–Si alloys, Ni–Fe alloys, and Ni–Co alloys. A vector hysteresis model based on a single hysteresis operator is then implemented and used for the prediction of the rotational magnetizations that have been measured in a sample of grain-oriented electrical steel. This is especially promising for FEM based calculations, where the magnetization state in each point must be recalculated at each time step. Finally, the computed loops, as well as the magnetic losses, are compared to the measured data.

This work discusses the vector measurement of the effective magnetic field inside a not oriented grain SiFe steel sample, taking into account the effect of the demagnetizing field. We propose an array of biaxial Hall sensors, placed up to the sample surface. The calibration of the system and a suitable extrapolation data strongly reduce the uncertainties of the direct measurement and provide an accurate evaluation of the magnetic field inside the material sample. Although the approach proposed can be also used for industrial frequencies, 50–60 Hz or more, the analysis is limited here to the static case, because we are mainly interested in static magnetic measurements. These measurements are especially useful for the vector characterization of soft magnetic materials and, in particular, for the identification and the experimental validation of vector hysteresis models. The experimental analysis presented in the paper deals with commercial not oriented grain SiFe steels. Experimental data about hysteresis loops and static power losses are given.

In this paper, we present a benchmark problem for the validation of numerical models of vector magnetic hysteresis. The problem geometry and the measurement system are described. The materials considered are both oriented grain (OG) and not OG Si-Fe steels. A series of experimental data about magnetic field and magnetic induction loci under rotational magnetization are presented with the corresponding magnetic losses. The measured data can be useful as a reference for the numerical models testing, comparison, and development. In addition, we propose here a comparison of the experimental data with the numerical results computed using a vector hysteresis model based on the extension of the Preisach model in 2-D.

In this work we present an identification procedure for a vector hysteresis model defined by a H-moving approach. The model parameters are identified by means of a suitable implementation of a genetic algorithm with a set of experimental data. The analytical formulation of the model and the characteristics of the genetic algorithm used are described. A comparison between computed data and experimental measurements for a not oriented grain Si–Fe magnetic steel with a weak lamination anisotropy are reported.

In this paper, we discuss the numerical modeling of hysteresis in magnetic steels with oriented and nonoriented grain. The modeling is fully 3-D, but it is applied here to typical 2-D magnetic problems. Starting from a vector generalization of the Preisach model, we introduce here the concept of an operative magnetic field, function of the state of magnetization of the material. This operative field is introduced to reproduce with more accuracy the peculiar behavior of Si-Fe steels approaching the saturation state. The properties of the model are discussed and some examples are reported.

This paper discusses the numerical implementation of a new vector hysteresis model, called the Della Torre, Pinzaglia and Cardelli (DPC) model, introduced as general hysteresis vector model for both isotropic and anisotropic magnetic materials. The present implementation is a 2-D one that uses any kind of hysteron described by the DPC formulation. Here some examples of numerical computation using Stoner-Wohlfarth-type hysterons are presented. The results computed by the model, applied to some basic vector hysteresis configurations, are in agreement with experimental behavior and model properties.

Muon triggering and offline muon identification are fundamental requirements for the LHCb experiment, which will begin to take data at the start-up of the LHC machine. The identification of muon particles and an estimate of the transverse momentum ( Δ p T / p T ∼ 20 % ) in the near-beam area of the first muon station is achieved by a set of 12 double triple-GEM detectors which covers an area of about 0.6 m 2 . Since b-quark production is peaked in the forward direction, GEM detectors will trigger about 20% of muons from B-particle decays. In this paper the results of the detector quality checks on anode and cathode panels planarity, GEM foil HV test, chamber gas leak and gain uniformity are presented. The performance of a chamber, composed of two triple-GEM detectors logically OR-ed, has been measured in a recent test beam at the SPS, with particle bunches with a time structure of 25 ns similar to the LHC running conditions. In this test the final front-end electronics and the final LHCb DAQ have been used. This result demonstrates that the detector can achieve the required performances (efficiency larger than 96%) at a detector gain of 4000, thus ensuring a long detector lifetime in the harsh LHCb environment.

This paper deals with a particular magnetic nondestructive technique applied to the control of the position of the steel blades in rotating parts of turbines and engines. The working principle is based on a bridge of four identical magneto-resistive sensors. One sensor is placed near the blades, and the change in magnetic field produced by a permanent magnet and deviated by the change in position of the blade is detected by the sensor bridge. The position of the sensor is indicated, via dedicated FEM simulations, in order to have high sensitivity to the position change and high output signal. The accuracy and effectiveness of the proposed method are shown by experimental tests carried out in our laboratories. In particular, the tests indicate that the proposed magnetic nondestructive technique can be used in an almost large velocity range, and for quite different values of blade tip. The method seems also promising for the detection of blade vibrations.

This paper deals with a neural network approach to model magnetic hysteresis at macro-magnetic scale. Such approach to the problem seems promising in order to couple the numerical treatment of magnetic hysteresis to FEM numerical solvers of the Maxwell's equations in time domain, as in case of the non-linear dynamic analysis of electrical machines, and other similar devices, making possible a full computer simulation in a reasonable time. The neural system proposed consists of four inputs representing the magnetic field and the magnetic inductions components at each time step and it is trained by 2-d measurements performed on the magnetic material to be modeled. The magnetic induction B is assumed as entry point and the output of the neural system returns the predicted value of the field H at the same time step. A suitable partitioning of the neural system, described in the paper, makes the computing process rather fast. Validations with experimental tests and simulations for non-symmetric and minor loops are presented.

In this paper, using suitable three-dimensional finite element method (FEM) approaches, either in frequency or in time domain, we will analyze the real magnetic behavior of a commercial Epstein machine, prescribed as standard magnetic measurement system. The analysis of magnetic field and eddy currents explains some facts that can affect the accuracy of Epstein frames as measuring systems for the magnetic characterization of laminated Si-Fe steels. The same FEM approaches shall be applied here to outline and define quantitatively some advantages in accuracy can be obtained using single sheet testers instead of Epstein frames.

This paper presents an experimental analysis of the rotational power losses of the magnetic materials of transformers, motors and actuators used in avionic environment. A large frequency range is investigated using a suitable experimental test frame developed to measure the power losses for a circular magnetization. The results about different silicon iron alloys with different textures and thickness are considered and compared.

A model for the vector magnetization of a distribution of particles with cubic anisotropy is presented. Recent work by the authors modeled the vector magnetization of a distribution of uniaxial particles by decomposing the total magnetization into reversible and irreversible components. In this paper, using an energy approach applicable to a generic plane, the model is extended to include cubic anisotropy projected to the (100) plane. The magnitude of the irreversible component is modeled using a Preisach differential-equation approach; however, other valid models can be used. The direction of the reversible component is modeled using the minimum energy approach of the classical Stoner–Wohlfarth model and taking into account the anisotropy field. The formulation of the generalized model is derived and its results are discussed considering (i) oscillation and rotational modes, (ii) lag angle, and (iii) magnetization trajectories.

In this work we discuss some procedures to increase the accuracy in the measurement of the magnetic field strength using Round Rotational Single Sheet Tester RRSST frames. The procedures are discussed jointly with the use of different magnetic field probes, such as flat coils and Hall sensors, and with a suitable shielding geometry. Experimental comparison between different methods and a discussion about the results is presented.

The aim of the paper is to highlight some of the innovative methodologies, techniques and systems for non-destructive electromagnetic testing, which have been developed in the framework of the AMDE project (Applications of Methods of Diagnostics Electromagnetic) partially funded by the Italian Ministry of University and Research. In particular, we will present the feasibility design of a suitable exciting-receiving coils configuration able to detect long defects by means of eddy-currents. To solve the forward eddy-current problem, advanced analysis tools have been developed and validated. In this paper, we will also introduce the approach for numerical simulations in the detection of the surface defects.

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. In particular the shape of the melt front and the critical transition velocity predicted are in agreement with the experimental observations.

The paper deals with a formulation of the charge simulation method (CSM), using surface charges in three-dimensional open-boundary and single-dielectric problems. The singularities of the integral functions are treated by a suitable change of variables, which gains a better numerical accuracy. The time-saving possibilities and the increase in accuracy of the proposed formulation are shown in a case of practical interest, where the results are compared to those obtained by means of the traditional CSM formulation with discrete charges and by means of finite element computer codes.

In this paper an approach to the numerical analysis of the electromagnetic interference (EMI) radiated by metallic grids, like Faraday 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 cage struck by lightning are given.

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.

This work deals with some energy properties of a vector thermal aftereffect model, recently presented. The model can compute magnetization and magnetic losses using an extension in 2-D of a Preisach-type approach. Some properties of the model are presented and discussed. An experimental validation is also included.

In this paper, the problem of the electromagnetic diffusion of electrostatic discharge (ESD) currents, interfering directly on the metallic enclosures of electronic equipment, and of the electromagnetic interference (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.

The present paper deals with the numerical simulation of the coupled problem of the transient diffusion of heat and current in conductive bodies. Moreover how to use the present approach taking into account the respective motion among systems of conductors is indicated in the paper. The final part of the paper deals with two examples of numerical calculation used to test the effectiveness of the method proposed and to show its practical possibilities. The results of the simulations are summarized in tables and pictures and are compared to experimental data and to numerical results obtained by means of other computer codes.

This paper deals with a numerical modelling of the interferences produced by electrostatic discharges (ESD) that reach the surface of metallic boxes containing electronic circuits and flow toward the ground connections. The waveform 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 a multipole expansion of the resulting current density distribution. >

The electrothermal behaviour of the muzzle-fed railgun configuration, proposed as remedy for the reduction of the velocity skin effect and its related losses in performance, is analysed in this paper by means of a suitable equivalent network approach, that is able to evaluate the distributions of the current density and the temperature in the conductive parts of the railgun. The use of magnetic field augmentation, both in self- and in external-augmented configuration, is proposed, to avoid too low values of the resulting accelerating action, and the dependence of the intensity of the augmentation on the geometrical factor is shown. Finally the possible effects in the reduction of the temperature rise located in the trailing edge zone, responsible for the transition of the armature from solid state to plasma arc are discussed by the analysis of the numerical simulation of shots presented. >

In this work we present a physical-related model of vector hysteresis for magnetic simulation of nanometric structures. The mathematical formulation, based on a generalization of the Preisach and Stoner-Wohlfarth models, is very simple and elegant. The numerical implementation is very easy and the computation time required for the simulations is extremely fast. However the accuracy is not comparable with the codes based on the micromagnetic theory, but it is sufficient for the use as preprocessing of more accurate and more complex methods, in order to speed up the convergence. In this paper the model identification is performed for a nanoscale spin valve using the data generated by a 3D micromagnetic code.

This paper deals with the mathematical definition of a general vector hysteresis operator in 3-D, as an extension of previous papers where the theory has been limited to the 2-D case. Although the paper is mainly focused on magnetic hysteresis, the definitions and the results reported can be applied to any general physical phenomenon that exhibits hysteresis. We show here the main general properties of the general hysteresis operator in 3-D.

This paper presents a discussion of the properties and the behavior of an unit magnetic particle as calculated by the DPC (Della Torre, Pinzaglia and Cardelli) model. The general mathematical expressions of the vector field generated by the unit magnetic particle are derived in a special regular parametric coordinates system. It is shown that, in a special case, the DPC model leads to the same results as in the Stoner-Wohlfarth dealing with the physics of an ellipsoidal, single-domain, uniaxial magnetic particle. Some numerical examples for a possible use of the DPC model in the analysis of nanomagnetic samples are presented.

Some analytical expressions for the calculation of the magnetic induction and the vector potential in iron-free media due to conductors in annular arc shape with regular cross section are reported. The algorithms derived, together with analogous algorithms reported previously for the calculation of the magnetic fields due to conductors in slab shape, can be used to calculate the magnetic fields in more complicated geometries and may be used to evaluate the self- and the mutual-inductance coefficients in systems with massive conductors.

In this paper we present a vector hysteron model, which is a generalization in three dimensions of the classical scalar Preisach model and an extension to the radial vector model previously published. We show that the vector model satisfies the second principle of thermodynamics. In addition the properties of the vector deletion and congruency are discussed. An example applied to a Si–Fe commercial steel is presented.

In this paper we present a single disk tester (SDT) developed for vector hysteresis measurements of magnetic steels. The measurement system deals with a stator of a 3-phase induction motor and some suitable magnetic field and magnetic induction probes. Numerical calculations based to a FEM approach in time domain and experimental tests are shown in order to describe both accuracy and efficiency of this measurement system.

Monitored Drift Tubes (MDT), filled with a mixture of Ar-CO2 at 3 bar pressure, are used as tracking devices for the ATLAS muon spectrometer at the Large Hadron Collider. MDT chambers were tested at the Roma Tre cosmic test site with the final version of front-end electronics, which provides information about the collected charge through a Wilkinson ADC. We present an analysis of the signal and timing characteristics in cosmic ray events, and of charge-dependent time response of the MDTs. A method to improve the spatial resolution of MDT chambers using the ADC information to correct the time response was developed. The procedure is based solely on the data from the MDT chamber itself. The results are compared with a simulation of the tube response with the Garfield program. (C) 2004 Elsevier B.V. All rights reserved.

An integral approach for the analysis of three-dimensional transient electromagnetic heating effects is presented. The conductor bodies are decomposed in elementary parallelepipeds, and the centers of nearby parallelepipeds are connected in order to obtain a three-dimensional grid. The electrical and thermal equilibrium equations applied to this grid allow the evaluation of the current density and the temperature distribution inside the conductors of the system. The characteristics of the approach are shown through simulations of the tests provided in the experimental verifications of switchgear and control gear assemblies. >

In this paper, we discuss a phenomenological approach for the numerical modeling of static hysteresis of grain oriented (GO) steels at macro-magnetic scale. The modeling is inspired to a generalization in 2-d of the Preisach model (this generalization can be easily extended in 3-d, but it is not necessary here), and the magnetization dependent state of the model parameters is represented by two distinct vectors, named the interaction field and the operative field, suitably defined. In this way, the very complex behavior of the GO steel circularly or linearly polarized is reproduced with accuracy, as shown in the numerical tests reported in the paper.

The production of the triple-GEM detectors for the innermost region of the first muon station of the LHCb experiment has started in February 2006, and is foreseen to be completed by the end of July. The final design of the detector and the construction procedure and tools, as well as the quality controls are defined. The performances of each detector, composed by two triple-GEM chambers equipped with dedicated CARDIAC-GEM front-end electronics, are studied with a cosmic ray telescope. The cosmic ray telescope has been set up including all the final off-detector components.

In this paper an integral approach for the analysis and the numerical simulation of the plasma armatures operating in rail launchers is tested by comparison with a differential approach. After a brief recall of the main theoretical and numerical aspects of the two approaches, a benchmark problem is presented and analyzed. The comparison between the results obtained confirms the validity and the effectiveness of both methods. Moreover, possible advantages or drawbacks of the computer codes implementing the two approaches are discussed.

The coupled problem of the three-dimensional diffusion of current and heat in railguns with a solid armature is formulated by means of a circuital approach. Rails and projectile are divided in a high number of small-size parallelepipeds, so that temperature and current density may be imagined uniform in every parallelepiped. By integrating Ohm's law over each parallelepiped an equivalent R-L electrical network is obtained, whose resistive and inductive parameters are evaluated by means of explicit analytical expressions, possible in the case of discretization in parallelepipeds. The voltage fall in the boundary layers between rail and moving armature are taken into account by means of suitable driven generators. The position of the projectile is deduced by the application of the virtual displacement principle, where the discretization in parallelepipeds allows one to express the Lorentz's force again by means of explicit analytical relations. The nonlinear differential equations system so obtained fully simulates the behaviour of a solid armature railgun, and is solved in time, updating at each time-step the coefficients variable with current density, temperature, and projectile displacement. >

This work deals with a finite difference frequency domain approach for the numerical computation of the current density distribution into non perfectly conductive plates in which a current is injected. The two-dimensional magnetic scalar formulation proposed allows to limit the discretization only to the current flow region, and the grid used for the finite difference numerical simulation comprises only the flat plate. The numerical model has been tested by comparison with the results obtained by means of analytical expressions, valid only under limiting conditions. Just to have an idea about the possible applications of the model proposed, the values of the internal impedance between two contact points of a rectangular ground plane, against the signal frequency have been computed. Moreover the influence of the shape of the plane, on the equivalent internal ground parameters, has been investigated, and the interfering current values in order to have a given ground overvoltage have been deduced. The results obtained encourage to develop three-dimensional magnetic scalar formulations in order to obtain a more realistic simulation of the diffusion of the current and to avoid errors and possible over-estimations due to the known limits of two-dimensional approaches.

In this paper a hybrid integral-finite difference approach for the analysis of the transient electromagnetic heating effects in three-dimensional conductor bodies, is presented. The electromagnetic analysis is carried out by the discretization of the conductive regions in suitable slabs, that allows the transformation of the Maxwell's equations to the equilibrium equation of an equivalent three-dimensional network. The thermal diffusion equation is solved by means of a finite difference approach in the time domain, using the same grid of the equivalent network above mentioned. The numerical solutions of the electrical and thermal equilibrium equations are performed separately and alternatively, and the values of the temperature dependent physical parameters are updated in time at each step. The method described in the paper has been tested with experimental data with regard to steady and transient state conditions of a bus-bars compartment of a low-voltage power center. >

The paper deals with the modelling of power busbar systems comparing two different numerical techniques. The first model develops a two-dimensional finite element procedure in the frequency domain and it can be generalized to the transient behaviour by means of the modified Fourier transform. The second model is based on a three-dimensional integral approach developed in the time domain. The methods have been applied to the steady state and transient analysis of busbar systems and a comparison of the results obtained by the two models has been carried out. In spite of the different features of the two models, the predictions are found to be in good agreement.