Ann Reimers

Fast Preisach-based magnetization model and fast inverse hysteresis model

Fast computational methods for Preisach-based models and their inverses are presented. The methods are based on a differential equation approach to computing a sequence of magnetization values due to a sequence of applied fields. The method used to speed up calculations can be applied to any Preisach model. The Della Torre, Oti, Kadar model was used here as an illustration. Sequential computations for the magnetization model are substantially faster than for standard Preisach models with comparable output error. Computations for the inverse hysteresis model are even faster than for the model. Using the inverse, open loop control of magnetic hysteresis is simulated, showing hysteretic material tracking a desired magnetization in a linear manner for both major loops and minor loops, with less than 2% error in inversion for the waveforms used. The effect of misidentification of material parameters on operation of the inverse is also investigated through simulations.

Fast Preisach based magnetostriction model for highly magnetostrictive materials

A Preisach based magnetization model is presented to work specifically on highly magnetostrictive materials. The model accounts for the additional anisotropy introduced when a prestress is used to activate the high strain, by using a bimodal structure. The necessity of strain feedback to deal with the magneto-mechanical effect is discussed for Terfenol-D specifically. The model is based on a fast implementation of the DOK magnetization model, so it is suitable for real time control applications.

Preisach modeling of aftereffect in a magneto-optical medium with perpendicular magnetization

Abstract The aftereffect of Co/Pt multilayer films with perpendicular magnetization has been measured with a magneto-optical Kerr effect (MOKE) magnetometer and calculated with a newly developed Preisach model. Compared to materials such as traditional magnetic recording media, Co/Pt multilayer films show a more complete picture of the progression of aftereffect because the magnetization of this material decays from saturation almost all the way to a ground state in a reasonable length of time. The magnetization measurements for times equal to negative and positive infinity are asymptotically horizontal, with a transition region that is linear on a logarithmic time scale. In contrast, typical published aftereffect analyses exhibit only a very small percentage of the total aftereffect that could be observed if time were not a factor in making measurements. A Preisach–Arrhenius model is used to calculate the magnetic aftereffect in the Co/Pt multilayer. Comparisons of the model to experimental results show not only the validity of the model, but also its value in predicting very short-time and long-time aftereffect behavior, and low levels of aftereffect occurring in noisy data, all of which are difficult to observe experimentally.

Isotropic media and the simplified vector Preisach model

This paper addresses an orientation error discovered when the simplified vector Preisach model (SVPM) was applied to an isotropic medium. For a smoothly rotating field, the magnetization of an isotropic medium should rotate smoothly. Instead, the SVPM predicts a ratcheting motion. A correction for this problem is suggested.

Implementation of the Preisach DOK magnetic hysteresis model in a commercial finite element package

The very accurate magnetic hysteresis representation available from Preisach-based models is not currently offered in commercial finite element (FE) packages. The major obstacle to using more accurate magnetization models is that they can cause convergence problems in the FE solution cycle. A method has been developed to integrate the fast DOK (Della Torre-Oti-Kadar) model, a Preisach based magnetization model, into the ANSYS FE program. Small-scale tests show that the FE solutions match expected values and that the use of the Preisach model does not effect the convergence of the FE solution.

Implementation of the simplified vector model

The simplified vector Preisach model (SVPM) is a three-dimensional (3-D) magnetization model developed for fast computations. In this paper, a new algorithm for the SVPM is detailed, which accomplishes two goals: 1) to extend the model from a two-dimensional to a 3-D model and 2) to provide efficient implementation of the model.

Preisach modeling of a magneto-optical medium with perpendicular magnetization

Magneto-optical Kerr effect measurements on a (0.3 nm Co/0.6 nm Pt)15 multilayer film with perpendicular magnetization showed Kerr rotation hysteresis loops that are very square, but asymmetric: on the descending major loop, while the magnetization decreases rapidly once the applied field approaches the coercive field, there is a long tail as saturation is approached. Modeling of this behavior was performed using a Preisach-based approach. To account for the known changes in magnetization behavior as a function of the number of bilayers, the Preisach density function was replaced by the sum of as many Gaussian distributions as there were bilayers in the material. The parameters of these Gaussian functions were systematically varied. The resulting model shows a good fit to both the experimental major loop and a first-order reversal curve.

A Preisach-type magnetostriction model for magnetic media

A Preisach-type model is modified to include magnetostriction. The stress-applied field relationship generated by the model displays the hysteresis observed in Terfenol-D, even though only a very simplified DOK model was used.

Energy considerations in vector magnetization models

Scalar magnetization model energy calculations, which are useful in calculating energy losses in open magnetization processes, are extended here to vector models. The energy loss is calculated as the difference between the energy input to the magnetic medium and the change in energy stored in the locally reversible component of the total magnetization. It is shown that under rotating magnetizing processes, the energy loss decreases as the material is saturated. For smaller rotating fields in anisotropic media, the magnetization lies between the applied field and the easy axis and the energy loss is not constant with rotation even if the magnitude of the field is constant.

Computation of inverse of magnetostriction model for Terfenol-D

Abstract The use of a non-linear model or non-linear inverse model in a control configuration has been shown to significantly improve the performance of actuators that use hysteretic materials to drive them. A method to calculate the inverse of a model for the hysteretic material Terfenol-D is presented here, to be used as part of a full control configuration for Terfenol-D actuators. This inverse is based on a magnetostriction model that has been shown to characterize the behavior of Terfenol-D well. Initially unbounded, accumulating errors in the inverse are analyzed and a method to bound the error for periodic input is presented. Simulations show steady-state tracking of strain waveforms that reach 95% of saturation to within 2% in an open-loop configuration. For use with inputs as high as 95% of saturation, though, the ratio of the input frequency to the sampling rate must be kept below specified levels. With inputs that reach only 85% of saturation, the error from inversion is below 0.2% and can be controlled by a parameter choice.