Armin Satz

Efficient energy minimization in finite-difference micromagnetics: Speeding up hysteresis computations

We implement an efficient energy-minimization algorithm for finite-difference micromagnetics that proofs especially useful for the computation of hysteresis loops. Compared to results obtained by time integration of the Landau-Lifshitz-Gilbert equation, a speedup of up to two orders of magnitude is gained. The method is implemented in a finite-difference code running on central processing units (CPUs) as well as graphics processing units (GPUs). This setup enables us to compute accurate hysteresis loops of large systems with a reasonable computational effort. As a benchmark, we solve the μMag standard problem #1 with a high spatial resolution and compare the results to the solution of the Landau-Lifshitz-Gilbert equation in terms of accuracy and computing time.

Macroscopic simulation of isotropic permanent magnets

Abstract Accurate simulations of isotropic permanent magnets require to take the magnetization process into account and consider the anisotropic, nonlinear, and hysteretic material behaviour near the saturation configuration. An efficient method for the solution of the magnetostatic Maxwell equations including the description of isotropic permanent magnets is presented. The algorithm can easily be implemented on top of existing finite element methods and does not require a full characterization of the hysteresis of the magnetic material. Strayfield measurements of an isotropic permanent magnet and simulation results are in good agreement and highlight the importance of a proper description of the isotropic material.

Reactivable passive radio-frequency identification temperature indicator

A low cost, passive radio-frequency identification (RFID) temperature indicator with (re-) activation at any point of time is presented. The capability to detect a temperature excursion is realized by magnets and a solution with a melting point at the critical temperature. As the critical temperature is exceeded, a magnetic indicator switches to non-reversible and this can be monitored via a giant magnetoresistance sensor connected to a RFID tag. Depending on the solutions or metal alloys, detection of critical temperatures in a wide range from below 0 °C and up to more than 100 °C is possible. The information if a threshold temperature was exceeded (indicator state) as well as the identification number, current temperature, and user defined data can be obtained via RFID.

Signal Analysis in Back Bias Speed Sensor Systems

Wheel speed sensors determine the angular velocity of rotating axes and are widely used in modern industry with a variety of applications. This paper provides a general introduction to back bias speed sensor systems, presenting and discussing the numerous parameters of a general 3D model. The underlying physical mechanisms of the back bias principle are explained with the help of 2D FEM magneto-static simulations. While 2D simulations do not perfectly reflect the magnetic field dynamics of the real problem, they provide an excellent qualitative understanding of the signal behavior concerning model parameter variations. Based on the previous discussions, a representative cogwheel geometry is proposed and analyzed in detail, featuring a study of the influences of the model parameters on the speed sensor signal. As an outcome of the parameter sensitivity analysis, it was possible to determine the degree of influence of the different model parameters on the quality of the speed sensor signal. In conclusion, this study aims to advance the general understanding of the speed sensor signal in back bias systems for manufacturers and to form a solid basis for future work in this field.

Unexpected Width of Minor Magnetic Hysteresis Loops in Nanostructures

We study the coercive fields and phase stability of magnetic nanostructures in hard axis loops and periodic rotational external magnetic fields over wide ranges of field amplitudes depending on the particle size and shape. For this purpose, we use a finite difference code with a gradient descent energy minimization algorithm. Our numerical simulations show that magnetic nanostructures can, in certain field amplitude regions, exhibit minor magnetic hysteresis loops with higher width than their major counterpart as well as variations in the coercive field for consecutive external field periods. The origin of the variations is chaotic behavior of the underlying magnetization processes leading to different residual domains after each field cycle.

Vortex magnetization state in a GMR spin-valve type field sensor

Micromagnetic sensors, viz., Hall elements, fluxgate, magnetoresistance and magnetoimpedance sensors, play a major role towards the miniaturization in the industrial society.

A device model framework for magnetoresistive sensors based on the Stoner–Wohlfarth model

Abstract The Stoner–Wohlfarth (SW) model provides an efficient analytical model to describe the behavior of magnetic layers within magnetoresistive sensors. Combined with a proper description of magneto-resistivity an efficient device model can be derived, which is necessary for an optimal electric circuit design. Parameters of the model are determined by global optimization of an application specific cost function which contains measured resistances for different applied fields. Several application cases are examined and used for validation of the device model.

Guidelines for cogwheel design optimized for back-bias speed sensor applications

Wheel speed sensors are commonly used in automotive applications where knowledge of the precise rotational velocity of the wheels is required to determine the vehicle speed or to obtain subtle information about tire pressure, road conditions or to steer modern driver assistance systems like the Electronic Stability Program. The conventional back-bias speed sensor solution requires the design of a proper target wheel that gives an optimal signal for specific, respective applications and magnetic sensors. In this work, typical geometric and material parameters of the cogwheel are identified and their influences on the speed signal are analyzed in detail. Data is acquired by finite element simulations that give an excellent understanding of how the speed signal behaves with a variation of the critical model parameters. The performed studies aim to provide guidelines for cogwheel manufacturers and for system engineers on how such wheels can be optimized for diverse applications.

New Modeling & Evaluation Approach for Capacitive Occupant Detection in Vehicles

Capacitive occupant detection is a contactless sensing technique which helps to improve safety standards in vehicles. This paper details the problem of relating measured sensor signals with physical model parameters. An innovative modeling approach is discussed, which takes into account different current pathways including also the influence of human passengers. Furthermore, a new electrode area variation method is introduced which allows to extract wanted model parameters. Finite Element Simulation shows that the proposed electrode area variation method is applicable for capacitive occupant detection sensors.