133 research outputs found
Anisotropy of losses in grain-oriented Fe-Si
Comprehensive assessment of the magnetic behavior of grain-oriented steel (GO) Fe-Si sheets, going beyond the conventional characterization at power frequencies along the rolling direction (RD), can be the source of much needed information for the optimal design of transformers and efficient rotating machines. However, the quasi-monocrystal character of the material is conducive, besides an obviously strong anisotropic response, to a dependence of the measured properties on the sample geometry whenever the field is applied along a direction different from the rolling and the transverse (TD) directions. In this work, we show that the energy losses, measured from 1 to 300 Hz on GO sheets cut along directions ranging from 0° to 90° with respect to RD, can be interpreted in terms of linear composition of the same quantities measured along RD and TD. This feature, which applies to both the DC and AC properties, resides on the sample geometry-independent character of the RD and TD magnetization and on the loss separation principle. This amounts to state that, as substantiated by magneto-optical observations, the very same domain wall mechanisms making the magnetization to evolve in the RD and TD sheets, respectively, independently combine and operate in due proportions in all the other cases. By relying on these concepts, which overcome the limitations inherent to the semi-empirical models of the literature, we can consistently describe the magnetic losses as a function of cutting angle and stacking fashion of GO strips at different peak polarization levels and different frequencies
Wideband magnetic losses and their interpretation in HGO steel sheets
The magnetic properties of high-permeability grain-oriented (HGO) Fe-Si sheets have been investigated in the frequency range 1 Hz-10 kHz, with attention devoted to the role of thickness on the behavior of the magnetic losses and the phenomenology of skin effect. The study is focused on the wideband response of 0.174 mm and 0.289 mm thick sheets, comparatively tested at peak polarization values ranging between 0.25 T and 1.7 T. The experiments associate fluxmetric measurements with direct Kerr observations of the dynamics of the domain walls. A picture of the magnetization process comes to light, where the dynamics of the flux reversal takes hold under increasing frequencies through the motion of increasingly bowed 180 degrees walls, eventually merging at the sheet surface for a fraction of the semi-period. This effect can be consistently predicted, starting from the Kerrbased knowledge of the equilibrium wall spacing, by the numerical modeling of the motion of an extended array of 180 degrees domain walls, subjected to the balanced action of the applied and eddy current fields, and the elastic reaction of the bowed walls. This model can be incorporated into the general concept of loss separation, by calculating the classical loss component through the solution of the Maxwell's diffusion equation under a magnetic constitutive law identified with the normal DC curve. The numerical domain wall model and the loss decomposition consistently predict that the excess loss component, playing a major role in these grain-oriented materials at power frequencies, tends to disappear in the upper induction-frequency corner
A simple compensation method for the accurate measurement of magnetic losses with a single strip tester
International audienceWe present a new method for the accurate characterization of soft magnetic sheets using a permeameter based on the precise compensation of the magnetomotive force (MMF) drop in the flux-closing yoke. It has been developed in order to overcome the systematic uncertainty affecting the value of the magnetic fieldstrength in single sheet testers when obtained, according to the standards, through the measurement of the magnetizing current. This phenomenon is more critical for high permeability materials, because of the reduced MMF drop across the sample. While additional sensors and auxiliary windings have been proposed in the literature, a novel approach is demonstrated here, based on the use of the permeameter upper half yoke as the MMF drop sensor and of an auxiliary winding on the lower half yoke, implementing compensation. This solution, dispensing one from dealing with the usually small signal levels of the conventional MMF drop sensors (e.g. Chattock coils), provides best results with the introduction of wedge-shaped magnetic poles, in order to accurately define the magnetic path length. The method is validated by measurements of power loss, apparent power, and hysteresis cycles on non-oriented and grain-oriented Fe-Si steel sheets, which are compared with local measurements performed on the same samples using H-coil and B-coil across a uniformly magnetized region
A novel magnetizer for 2D broadband characterization of steel sheets and soft magnetic composites
Power losses in thick steel laminations with hysteresis
Magnetic power losses have been experimentally investigated and theoretically predicted over a range of frequencies (direct current—1.5 kHz) and peak inductions (0.5-1.5 T) in 1‐mm‐thick FeSi 2 wt. % laminations. The direct current hysteresis properties of the system are described by the Preisach model, with the Preisach distribution function reconstructed from the measurement of the recoil magnetization curve (Bp=1.7 T). On this basis, the time behavior of the magnetic induction vs frequency at different lamination depths is calculated by a finite element method numerical solution of Maxwell equations, which takes explicitly into account the Preisach model hysteretic B(H) relationship. The computed loop shapes are, in general, in good agreement with the measured ones. The power loss dependence on frequency is predicted and experimentally found to change from a ∼f3/2 to a ∼f2 law with increasing peak induction
Hysteresis and Avalanches in the Random Anisotropy Ising Model
The behaviour of the Random Anisotropy Ising model at T=0 under local
relaxation dynamics is studied. The model includes a dominant ferromagnetic
interaction and assumes an infinite anisotropy at each site along local
anisotropy axes which are randomly aligned. Two different random distributions
of anisotropy axes have been studied. Both are characterized by a parameter
that allows control of the degree of disorder in the system. By using numerical
simulations we analyze the hysteresis loop properties and characterize the
statistical distribution of avalanches occuring during the metastable evolution
of the system driven by an external field. A disorder-induced critical point is
found in which the hysteresis loop changes from displaying a typical
ferromagnetic magnetization jump to a rather smooth loop exhibiting only tiny
avalanches. The critical point is characterized by a set of critical exponents,
which are consistent with the universal values proposed from the study of other
simpler models.Comment: 40 pages, 21 figures, Accepted for publication in Phys. Rev.
Soft magnetic properties of high-temperature nanocrystalline alloys: Permeability and magnetoimpedance.
The technological applicability of FeCoNbBCu alloys is suggested in terms of measurements of
room temperature magnetoimpedance and temperature dependence of magnetic permeability
m
r
.
Results for the Fe
78-
x
Co
x
Nb
6
B
15
Cu
1
alloy series show that room temperature soft magnetic
properties are enhanced in the lowest Co containing alloy (
m
r
;
10 500 and magnetoimpedance ratio
;
60% at 1 MHz
!
. However, permeability exhibits a smoother thermal dependence in the alloys with
medium and high Co content. A tradeoff between magnetic softness and its thermal stability reveals
the alloy with 39 at. % Co as the most suitable composition among those studied, characterized by
a temperature coefficient of
;
0.02%/K from room temperature up to 900 K. This value is 1 order
of magnitude smaller than those observed for FeSiBCuNb
~
FINEMET-type
!
alloys and Mn ferrites
and extended over a much wider temperature range than in these materials
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