IEEE Transactions on Magnetics

We report the first demonstration of a magnetoresistive random access memory (MRAM) circuit incorporating MgO-based magnetic tunnel junction (MTJ) material for higher performance. We compare our results to those of AlOx-based devices, and we discuss the MTJ process optimization and material changes that made the demonstration possible. We present data on key MTJ material attributes for different o... View full abstract»

This paper reports on preparation of a magnetically anisotropic polycrystalline hexaferrite, Sr Ca Fe O , whose orientation degree is as high as 100%. The preparation uses standard ceramic techniques, including wet press... View full abstract»

This paper focuses on the development of a homogenized energy model which quantifies certain facets of the direct magnetomechanical effect. In the first step of the development, Gibbs energy analysis at the lattice level is combined with Boltzmann principles to quantify the local average magnetization as a function of input fields and stresses. A macroscopic magnetization model, which incorporates... View full abstract»

This paper uses the solutions of the linearized Landau–Lifshitz equation to establish the limitations of coherent precession models. Contrary to traditional argument, such models are valid only in the limit of vanishing surface anisotropy. The paper examines the theoretical basis for this conclusion in the context of an idealized magnetic surface. It considers several practical examples in w... View full abstract»

This paper discusses the use of the inverted ( -based) Preisach model and its incorporation into the finite-element method (FEM). First, the -based Preisach model is studied thoroughly along with the forward ( -based) Preisach model, highlighting the advantages and disadvantages ... View full abstract»

In this paper, we propose an improved method of characterizing highly permeable magnetic materials. The method is experimentally simple, inexpensive, and more accurate than that in IEEE Standard 393-1991. Our method places special emphasis on determining magnetic characteristics during saturated conditions. View full abstract»

This paper describes a versatile exposure system for the reproduction of static and extremely low-frequency (ELF) magnetic fields. The system can be used for in vitro and in vivo experiments. The exposure setup consists of six circular loops, each placed on the face of a cubical box and suitably fed. The paper shows, by means of a genetic-algorithm approach to optimize the degrees of freedom of th... View full abstract»

We introduce a symplectic finite-difference time-domain method for electromagnetic field simulation. Our method can successfully solve Maxwell equations involving conductor loss, which cannot be solved by the symplectic integration methods that have been presented in previous works. A class of high-order symplectic schemes for computing the time-dependent electric and magnetic fields are derived o... View full abstract»

Increasing energy cost and advance in permanent magnet technology have provided the incentives to develop geometrically compact and energy-efficient electromagnetic (EM) actuators. Design of electromagnetic (EM) actuators often involves solving a magnetic field problem. This paper presents an adaptive meshless method (MLM) that inherits many advantages of the finite-element method (FEM) but needs ... View full abstract»

This paper describes a two-dimensional finite-element analysis of an 8/6 switched reluctance motor with static eccentricity. It describes the influence of the eccentricity on the static characteristics of the motor and shows how to obtain flux lines, flux density distribution, and the flux-linkage/rotor angular position characteristic of the motor in both healthy and faulty conditions, as well as ... View full abstract»

This paper describes an analytical model that includes end effects for ironless synchronous permanent-magnet planar actuators. Because of its flexibility, the model can be used to predict the performance of various permanent-magnet array and coil array topologies and commutation schemes. Moreover, since control currents have to be nonsinusoidal, it allows analysis of the motor performance without ... View full abstract»

In this paper, we address the imaging of the spatial distribution of the resistivity of conductive materials by using data from eddy-current nondestructive testing. Specifically, the data consists of measurements of the impedance matrix at several frequencies acquired using a coil array. The imaging method processes the second-order term (estimated from the measured data) of the power series expan... View full abstract»

In this paper, we calculate the transient eddy-current response of a driver pickup probe due to a conducting plate by means of series expansions. We consider an excitation current in the driver coil that rises exponentially with time toward a constant value, the step function current being a special case with zero time constant. We find the transient response from the frequency domain expressions ... View full abstract»

Passive magnetic bearings are an attractive alternative to conventional ball bearings in applications where wear and tear must be minimal and cost or construction restrictions ban the use of active magnetic bearings. They also find applications as miniaturized high-speed bearings where no other low-friction solutions are available. We show that, for a given cylindrical construction volume, an opti... View full abstract»

We present efficiency and scaling relationships for dc (i.e., noninduction) constant inductance gradient electromagnetic launchers. We derive expressions for electromagnetic force, efficiency, back-voltage, and kinetic power in terms of electrical circuit parameters. We show that launcher efficiency is a simple function of armature velocity and the launcher's characteristic velocity. The character... View full abstract»

In this paper, we present a novel electromagnetic actuation scheme for nanoscale positioning with a six-axis magnetic-levitation (Maglev) stage, whose position resolution is 3 nm over an extended travel range of 5 5 mm in the - plane. We describe the conceptualization ... View full abstract»

This paper describes the topology of a permanent-magnet polarized reluctance actuator that enhances the performance of electromagnetic valve actuation systems; specifically, it reduces losses during extended periods of valve closure, improves controllability, provides a degree of fail-safe operation in the event of a system fault, and reduces currents required for system initiation during cold-sta... View full abstract»

This paper presents a simple and economical way to accurately estimate an initial position for linear hybrid stepping motor (LHSM) drives by utilizing dc excitation. In order to detect an absolute position of the mover, two preliminary tests are carried out under two different dc conditions: single-phase and two-phase dc excitation. The proposed algorithm has been successfully applied to a practic... View full abstract»

This paper reports on the development of a spherical actuator with two actuated degrees of freedom (DOFs). The electromechanical conversion principle is that of an induction motor. The paper first discusses possibilities of adapting the actuator to a spherical rotor actuated with an unlimited angular range along two DOFs. These concepts are then characterized and compared by analytical and numeric... View full abstract»

Reliability of modern hard disk drives (HDDs) is a major concern especially with decreasing head-to-disk spacing in order to attain higher recording densities. One of the reasons for HDD failure is the occurrence of intermittent or sustained head–disk contacts. It is therefore important to be able to detect such head–disk contacts early on so that backup safety schemes can be implement... View full abstract»

This paper discusses the cancellation of linear intersymbol interference (ISI) in two-dimensional (2-D) systems. It develops a theory for the error rate of receivers that use tentative decisions to cancel ISI. It also formulates precise conditions under which such ISI cancellation can be applied effectively. For many 2-D systems, these conditions are easily met, and therefore the application of IS... View full abstract»

We have performed an experimental characterization of hybrid temperature and frequency effects on the performance of on-chip square transformers. Using measured two-port S-parameters at different temperatures, we extracted and compared the maximum available gain and fractional power loss in each of thre... View full abstract»