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The accuracy of finite element approximation on tetrahedral elements is studied using the previously derived maximum eigenvalue condition. This condition is linked with the minimum singular value of the element 'edge shape matrix' that characterizes the flatness of an element. A geometric interpretation of these results is discussed. From the theoretical viewpoint, a better insight into the mechanism of approximation errors is gained. From the practical perspective, a precise characterization of shape of tetrahedral elements becomes possible. Index terms - finite elements, tetrahedral mesh, error estimate, approximation, interpolation, shape, singular value

3-D optimization method using the combined experimental design method and direct search method is developed to apply to the optimal design of a permanent magnet type of retarder. It is shown that the braking torque is increased by using the optimization method. The CPU time can be considerably reduced by utilizing the initial values obtained by the experimental design method. Index terms - Optimization, finite element method, direct search method, retarder, eddy current

In a linear induction launcher, both the barrel and the projectile are of finite length. This causes the force-displacement curve to have a jagged shape. The reasons are: the barrel is partitioned into sections; end effects are present; dc components exist in the input currents; and the drive coils are of finite width. The first three factors were dealt with in our previous publications. This paper describes how to improve the performance of a four-section linear induction coil launcher, powered by synchronous generators, by redesigning the drive coils so that they may be fed by a five-phase source rather than the customary three. The paper presents the drive-coil design criteria, the reasoning behind the selection of the firing sequence for each of the four sections, and the improved accelerating force curve. Index Terms--Coil launchers, efficiency, linear induction launchers, polyphase currents.

This paper describes a preliminary experimental investigation to convey acceleration measurements, made on-board an electromagnetic (EM) launched projectile, using microwave telemetry techniques. The focus of the investigation is to extend the Hardened Subminiature Telemetry and Sensor Systems (HSTSS) technology for use in EM launch environments. Many aspects of the HSTSS technology have already been successfully demonstrated in high-G, high-pressure launch environments in conventional gun systems. In addition, microwave transmission in stationary experiments, where the telemetry package was exposed to relatively high magnetic fields and EM transients in a railgun launcher, has been demonstrated. However, microwave telemetry during an EM launch has not been demonstrated until now. In this work, setback acceleration measurements obtained with an on-board accelerometer were processed by HSTSS electronics and transmitted simultaneously during launch via an antenna located in front of the EM launch package. While only the test conducted at 9-kG peak acceleration provided the most useful data, detailed analyses suggest that mechanical problems--rather than the microwave telemetry process itself--were probably responsible for difficulties experienced at higher accelerations. This paper reviews the experimental methodology and discusses the results of the investigation. Index Terms--Accelerometer, FM, hardened, RF, S-band.

The 'magnetic obturator' is an armature concept developed by IAP Research in the late 1980s. Advantages of the magnetic obturator include lower mass than conventional 'C-type' railgun armatures (approaching the theoretical minimum mass), compatibility with mid-drive sabots, and the potential for nontransitioning operation. The Institute for Advanced Technology (IAT) at The University of Texas at Austin began testing magnetic obturators in 1997. Our tests showed that magnetic obturators can operate very well, but not yet as reliably as C-type armatures. This paper discusses experiments conducted to understand and resolve several recurrent problems that include difficulties associated with start-up, high contact pressures leading to local yielding of copper rails, and susceptibility to develop intermittent arcing contact before transition. This paper reports our progress in addressing these three areas and presents recommendations for further research. Index Terms--Armature, railgun, transition, wear.

This paper presents a magnetic field analysis of a moving magnetic field type sensor with shading coils developed for eddy current testing. The cracks and defects that are very difficult to detect with the conventional method, can be detected by using this sensor. In this paper, we have carried out the magnetic field analysis with the 2-D and 3-D finite element methods to show the effectiveness of this sensor. Index terms - Moving magnetic field, shading coil, eddy current testing, finite element method.

This paper presents the three-dimensional electromagnetic, structural-dynamic and acoustic calculation of electric machines with respect to induction furnaces and gives hints for optimization of complex vibrating structures. The method chosen to compute the acoustic field is the Boundary Element Method, which solves the Helmholtz equation in the three dimensional case and considers scattering and symmetry of large scale structures [3]. The results presented in this paper show the advantage of BEM concerning calculation time and computation resources. The aim of the work is to optimize the acoustic behavior of the structure in such a way that noise emission of the machine will decrease. Several modifications are proposed and also calculated and show good results in comparison to the unmodified model. Index terms - Induction heating, Acoustic noise, Boundary element methods, Electromagnetic forces, Finite element methods

This paper presents a formulation of a numerical integrator for charged particles. The original idea of the integrator scheme was already given several years ago. Main topics of this paper is reformulation of the integrator as the Lorentz group Lie algebra map and modifications for practical use. Two numerical simulation examples, trapped electron motion in cusp magnetic field and electron pendulum motion in the Free Electron Laser (FEL), show validity of this new formulation. Index terms - Particle beam, Integrator, Numerical analysis

Three-dimensional Finite Element Method (FEM) has been widely applied for practical analysis use of electromagnetic field. However, numerical error estimation methods which focuses on the governing equations of electromagnetic field, not FEM formulations, have been reported in few papers. This paper proposes a new posteriori error estimation concept based on Ampere's circuital law which is one of the basic equations of electromagnetic field. Numerical error is quantitatively estimated as the current value which should be equivalent to the exciting current of the field. Index Terms - Ampere's circuital law, posteriori error estimation, three-dimensional FEM

The paper introduces a new FEM technique for considering eddy-currents in multi-conductor windings surrounded by magnetically nonlinear media. Traditional finite element formulation is combined with the so called elimination of inner nodes to achieve fast solution. The effectiveness and 'behavior' of the technique was investigated. The presented results are discussed and finally concluded in the paper. Index terms - Eddy currents, machine windings, finite element methods, elimination.

The cogging torque and dynamic performance of a newly designed single phase brushless DC motor have been investigated in this paper. The single phase brushless spindle motor is usually applied for cooling fan, pump and blower before the performance is improved by the reengineering process. The stator configuration and the drive circuit have been remodeled in order to meet the requirements of the spindle motor used in the DVD and HDD applications. The cogging torque is reduced to 18 g-cm by the salient pole reshaped. An automatic phase adjuster is also introduced to improve the performance of the dynamic characteristics of a single phase spindle motor in this paper. According to the test results, the maximum speed could be increased from 6500 rpm to 12000 rpm and the efficiency from 22% to 38%. A single phase motor has been demonstrated successfully used in the HDD and DVD application by reshaping for the salient pole and phase adjusted automatically with the rotation speed in this paper. Index term - automatic phase adjuster, cogging torque, single phase spindle motor.

This paper introduces a novel design of hybrid hydrodynamic and aerodynamic fluid bearing system. The fluid bearing system consists of an oil lubricated journal bearing unit with herringbone grooves and an air lubricated thrust bearing unit having a conical thrust plate engraved with spiral grooves. This bearing system has lower power consumption and enables a reliable seal design only for its journal bearings. The spindle motor with this bearing system has been prototyped. In this paper some simulation and testing results are reported. Index Terms - Fluid film bearing, hard disk drive, hybrid design, spindle motor.

A two-dimensional sensitivity function, describing the down-track and cross-track responses of a MR head, is derived starting from a microtrack formed with a maximal-length Pseudo Random Binary Sequence (PRBS). This sensitivity function is built up from a set of 'Extracted Dipulse' responses each taken with the readback head in a different off-track position with respect to the microtrack. The resulting two-dimensional function represents the sensitivity to a 'unit magnet' with a length of one channel bit, rather than to the vertical field component alone. There are two advantages to this approach: First, the sensitivity to high frequency signal components is much enhanced and the signals used are generally much more representative of written data. Second, this method has the ability to quantify both linear and nonlinear readback distortions as a function of offtrack position. This paper initially describes the practical procedure used to obtain the sensitivity function. An advantage of this procedure is that you do not need to have a clock channel for the timing alignment of the dipulses as they are already tied to the bit-cell positions. In the latter half of the paper, this procedure is used to analyze the effects of 'read-write non-parallelism' a condition wherein, the MR stripe reads the transitions at a skew due to a manufacturing defect or otherwise. In other words, it is probed whether a cross-track variation in head sensitivity would contribute towards the so-called 'deterministic off-track peak jitter' and also whether a relative skew between read and write operations can influence the head sensitivity function and aggravate the deterministic peak-jitter. The answers we got for both the questions were in the negative. There was no any deterministic trend in peak-position variation (as against the trends that we got with full-width tracks) with or without a skew and the head sensitivity function was also not affected by a skew.

This paper explores the high speed and high power aspects of fast writing in magnetic data storage. It describes the experimental methods and instrumentation needed to exercise thin-film write heads at excessively large write currents (< 0.5 A), short pulse durations ([greater than or equal to]200 ps) and high frequencies (< 1 GHz). The not commercially available instrumentation used is discussed in detail (avalanche pulse generator, head interconnect circuit). The thermal behavior of the head is investigated to ensure that the temperature of the hottest yoke leg ([P.sub.2]) does not exceed 250 [degrees] C to avoid thermal degradation of the magnetic performance. The paper describes various pulse write, AC-bias write and AC-burst erase methods. As an example, experimental results obtained for an 'industry-typical' head are reported and discussed, viz. head footprints, saturation curves, write current needed for media magnetization reversal down to 200 ps, write field gradients, write field growth rates, high-frequency head efficiency, current levels needed for AC erasure versus frequency, and AC-bias writing results.

As the power density requirement for new compulsator (CPA) designs increases, designers are driven to use more composites to reduce mass, spin the rotors faster to store more energy, and operate the machine at higher voltages to increase machine power output. In any particular compulsator design, the rotor windings are subjected to high strain levels as the rotor is spun and experiences radial growth. A critical component in the rotor winding design is the high voltage insulation. As the rotor is spun, the induced strains are applied to the insulation system on the coil conductors. This implies that over the operating life of a compulsator, the coil structure and the high voltage insulation must remain structurally intact, while undergoing repeated cyclic loading. This paper presents the design and testing of a compulsator rotor winding that has been recently fabricated at the Center for Electromechanics at The University of Texas at Austin. The paper focuses on the testing done both at room and elevated temperature to evaluate the winding structure and high voltage insulation system under both tensile and transverse strain conditions. Data presented suggests a factor of safety of at least five for strain to failure values and high voltage insulation good for at least twice line voltage after testing to strain failure.

The Department of Defense (DoD) and commercial entities are dependent on chemical plating and coating processes to replace worn or eroded material on damaged parts. Logistics Centers have been forced to consider replacement materials for repair operations due to the tightening of government regulations on the use of toxic and hazardous materials. This paper describes a new process capable of fulfilling many of these requirements. Existing state of the art thermal spray processes (HVOF, D-gun, plasma spray) are limited to powder velocities of about 1 km/s because they rely on the thermodynamic expansion of gases. A new thermal spray process using electromagnetic forces can accelerate powder particles to a final velocity in excess of 2 km/s. At this velocity, powder particles have sufficient kinetic energy to melt their own mass and an equivalent substrate mass on impact. The energetics of the process allow fusion bonding of greater strength than that created by low velocity processes as well as improved coating density. This paper will describe the laboratory system designed and constructed to conduct proof of principle experiments. Results of the experiments will be presented along with high speed photographs of powder particles confirming system modeling and performance. The paper will conclude with a discussion of the future direction of the program.

Today electrodischarge light-gas launcher (EDL) is not only the subject of investigation, but suitable tool for different kinds of explorations. Such hypervelocity accelerator gives the possibility to carry out the experiments on impact interaction in the wide range of velocities (up to several kilometers per second) with the substantial accelerated bodies masses. This experiment demands the creation of special impactor that, in its turn, requires the launch package design. This paper considers the development of launch package for multiple rod hypervelocity impact investigation. Distinctive features of multiple rod impact investigation are the requirements to the simultaneity and desired impact geometry of interaction (mutual position of penetrators and approach angle). To meet all mentioned demands penetrators were placed in inseparable holding cartridge. The exact approach angle was ensured by means of aerodynamic stabilization. The holding cartridge has to be made from materials with least possible density to decrease its influence on interaction process. At the same time the holding cartridge has to be strong enough to withstand the overloads during the in-bore acceleration. In this paper the design and test results of the launch package for the multiple rod hypervelocity impact studying are presented. All experiments were carried out with the (EDL) of 30-mm caliber. Hydrogen under the initial pressure of 40 MPa was used as a working gas. It permits us to use the projectiles with masses up to 150 g and explore the velocity range from 1500 up to 3000 m/s. Index terms - head stabilization, separation flow, spiked body, disk tip.

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. ln particular the shape of the melt front and the critical transition velocity predicted are in agreement with the experimental observations. Index Terms - Integral equations, Railguns, Skin effect, Transition metal materials.

The study of electromagnetic launch techniques and the funds invested in that regard have been justified by many on the basis of tactical application of the technology. In order for these studies to be more than academic exercise, their long term goals and near term objectives must be part of a path toward a system assembly consistent with the efficiency, volume and mass requirements of viable tactical applications. in addition, it is not suitable in this context to pursue techniques, which may be lower risk in their own right, but place unacceptable or unachievable demands on other components within the system. Selection of development alternatives should not be made based on component figures of merit alone, but should consider the interactions and interfaces between components and subsystems such as discharge reaction torque, projectile acceleration profile, charging requirements, heat rejection requirements, parasitic mass and overall system efficiency. When taken in that perspective, approaches considered suboptimal as components can contribute to improved system viability. Evaluation of EM armament characteristics should be conducted in the technology environment of future systems. Combining electric combat vehicle requirements for energy storage and pulsed power into integrated subsystems dramatically reduces armament space and weight claims. Significant advantages have been quantified for EM armament in that context which are unavailable for other approaches. Achieving these benefits requires development of subsystems which meet aggressive, but attainable goals. Previous analyses have investigated the system impact of EM armament with efficiencies, volumes and auxiliary requirements derived from specific subsystem configurations. This paper presents a portion of an analyses to determine what performance levels EML subsystems must achieve to enable EM armament in future weapons systems. In particular, this paper presents the sensitivity of EML viability to (1) the power per unit volume of a pulsed power supply, (2) the efficiency of that power supply, (3) the launch event efficiency, (4) the number of rounds stowed, and (5) the maximum projectile energy attainable. The result is a definition of the minimum performance levels useful for the tactical application considered. Development of alternatives that do not recognize these high system level requirements will not lead to tactical advantages compared to conventional systems. This analysis indicates that EML technology can provide a viable armament alternative for future armored land combat systems requiring high energy projectiles and high on-board projectile count. In order to achieve that goal pulsed power supplies must realize 8000 kW/[m.sup.3] with efficiency exceeding 60%. In addition, the pulsed power must support a system including launch efficiency exceeding 70% for large caliber or 55% for medium caliber armament. Index Terms - electromagnetic launchers, combat vehicles, hybrid electric, Army After Next

In 1994, Dreizin and Barber [1] presented an analysis of the muzzle voltage developed in a railgun with a solid contact armature. They showed that there is a significant contribution to the measured muzzle voltage arising from the current flow in the rails ahead of the armature. They further argued that this voltage is influenced by velocity skin effect and that it may become the dominant effect on muzzle voltage at high velocity. The results of that paper, although on solid theoretical foundations, generated some controversy because many previous investigations of armature behavior had obtained good agreement between theory and observation without taking this term into account. In this paper, a novel experimental technique is described that permits direct observation of the effect of precursor rail current on muzzle voltage. The observed magnitude of the voltage is in agreement with the estimates provided by Dreizin and Barber, including the contribution of velocity skin effect. Index Terms - experimental measurement, muzzle voltage, railgun, velocity skin effect.

This paper presents a generic discussion on compensation in pulsed alternators. It covers all aspects of compensation i.e., types of compensation, alternative methods for the physical realization of the various compensation schemes, the pros and cons of compensation or the rationale for compensation The intent of this paper is to form a guiding reference on the issues of compensation in pulsed machinery.

This paper analyzes the magnetic characteristics of brushless permanent-magnet motors with embedded magnets. It shows that the flux leakage has a substantial effect on the air gap flux density interacting directly with the armature current to produce torque. The flux leakage parameters [Eta] and [Lambda] are expressed analytically in terms of the magnetic material properties and the motor dimensions. They are essential quantities for the accurate prediction of the average flux densities within the air gap and the magnet. The finite element numerical method is adopted to verify the analytical model. For the numerical example in this paper, the average deviation between the finite element result and the analytical one is about 1-2%. This finding confirms the suitability of the analytical model for the design purpose. Although design is not particularly emphasized in this paper, one section gives a simple explanation of flux leakage considerations in magnet design. Index Terms - Brushless, embedded magnet, flux leakage, permanent magnet.

This paper presents the analysis of a transverse flux induction furnace. The originality of the analysis presented in this paper is to use successively three different formulations in order to solve the magneto-thermal coupled problem. The Whitney elements (node based, edge based, facet based and volume based elements) are shown to be a convenient mean to perform naturally that coupling and to fullfil convergence conditions for the iterative solver. Index terms - Coupling, eddy currents, electromagnetic heating, finite element methods, induction heating, thermal devices.

This paper presents a method of alternately switched coils in transverse flux inductive heating devices (TFIH) and their finite element formulation in order to improve temperature distribution. In the present paper the application of the boundary impedance method in eddy-current computation in thin conducting sheets is combined with the transient calculation of the resulting temperature distribution. In this non-linear coupled electromagnetothermal problem the [Mathematical Expression Omitted] formulation is used to calculate the time-harmonic electromagnetic field. The Fourier's thermal conduction equation is extended by terms for conduction, convection and radiation. In addition a quasi steady state formulation for high switching frequencies is introduced. Index terms - Induction heating, Transient analysis, FDTD methods, Finite element methods

This paper presents a numerical method for steady state calculations for a relay. For this purpose the A, A-V method has been selected. The nonlinearity of the materials are taking into account. In this method the three dimensional eddy currents equations are formulated in terms of a magnetic vector potential A and an electric scalar potential V in the conducting region and only the magnetic vector potential elsewhere. In the paper it is assumed that the material has orthotropic characteristic. Index terms - Finite difference methods, electromagnetic analysis, eddy currents, nonlinear magnetics, relays.

An efficient approach for calculating the short-circuit reactance of transformers is presented in this paper. This approach is based on the surface magnetic charge method and the band-ring mesh elements. The area integral in the calculation of the magnetic flux is transformed to a line integral, which can save on computing time and increase the calculation accuracy. The integral transformation results from the idea of the flux decomposition. Furthermore, based on the flux decomposition, a unified formula of calculating the short-circuit reactance of transformers is derived. The calculation of the formula is simplified by employing the band-ring boundary elements in the particular geometrical situation that the cylindrical windings and the elements are coaxial. Calculation examples illustrate that the approach presented in this paper is both efficient and accurate. Index terms - Transformers, impedance, magnetic fields, surface magnetic charge methods.

In this paper a general infinite element is presented which can be used in the termination of finite element meshes for scattering electromagnetic problems. The new infinite element uses an increased number of nodes in the radial direction which provides it with much improved absorption over the previously presented infinite elements. This paper will demonstrate that the previously reported two noded and four noded infinite elements are inferior in performance compared to the Bayliss Turkel absorbing boundary condition and that the multi-noded infinite element is able to give comparable results to the Bayliss Turkel ABC. Index terms - Electromagnetic scattering, Finite element methods, Radar cross sections, Modelling, Infinite elements.

In the paper the problem of optimization by shape derivative has been presented. The approach allows to obtain the domain required by the so called continuous gradient approach which consists in calculating gradient before discretization and the gradient is discretized. It has advantages to the classical approaches which proceed just inversely. The paper gives examples coming from electrostatic field which are to illustrate the effectiveness of the method. Index terms - shape derivative, material derivative, optimal shape design

This paper presents inverse analysis which is formulated by boundary element method(BEM) with Laplace transform and the matrices for inverse analysis are stabilized with singular value decomposition and fuzzy inference. The proposed method is applied to crack shape identification on an eddy current testing(ECT). In conventional method, some crack shapes can not be obtained because of an ill-posed problem, the new method can identify crack shapes by stabilizing the matrices. In this paper, it is shown that the proposed method is applicable to the crack shape estimation of ECT. Index terms - Laplace transform BEM, ECT model, inverse problem, singular value decomposition, fuzzy inference.

In this paper design sensitivity analysis is applied to solve the TEAM workshop problem 25. In order to justify the use of a gradient method, it is necessary to assume a continuously differentiable dependence of the stiffness matrix on the design parameters. Since design sensitivity analysis is mainly applicable to optimization problems, where the geometrical parameters undergo small changes only - which is not the case for the problem investigated in this paper - a procedure is proposed, which allows this method to be applied also when the changes in geometry are significant. Index terms - Optimization methods, Sensitivity, Magnetostatics, Shape, Nonlinear Magnetics, Finite element methods

The paper presents an efficient approach based on the adjoint field technique (AFT) for calculating first order sensitivities of 3D nonlinear magnetic devices to geometric parameters. The sensitivities thus calculated are useful in the devices' (re)design. The design of a nonlinear inductor with imposed flux-current characteristic is formulated as an optimization problem. An algorithm based on geometric sensitivities is used to solve this problem. The general theory and the application presented in the paper prove that AFT is effective not only for linear problems, but for nonlinear ones as well. Index terms - Electromagnetic analysis, nonlinear magnetics, sensitivity, optimization methods, ferromagnetic materials/devices, adjoint field technique.

This paper describes the implementation of the Rusck's theory of lightning induced voltages on transmission lines in the Electromagnetic Transients Program (EMTP). After summarizing the theory, the paper presents aspects of the implementation such as interfacing problems between Rusck's model and the EMTP. The paper also presents a study on the influence of losses in transmission lines using, as an example, waveforms of actual measured induced voltages in a distribution line. Index terms - Power system transients, power system lightning effects, power system simulation.

Most papers concerning the calculation of 3D eddy current problems are using a combination of a vector potential and a scalar potential to solve the electromagnetic field in conducting regions. This paper presents the [Mathematical Expression Omitted], [Mathematical Expression Omitted] formulation using both the magnetic vector potential [Mathematical Expression Omitted] and the electric vector potential [Mathematical Expression Omitted] for the eddy current regions. Since nodal vector potentials with continuous normal components have accuracy problems at interfaces of regions with different permeabilities, edge elements are used for both potentials. The advantages of the presented formulation compared to the mentioned well-known formulations are described in detail. The formulation is applied on the computation of the 3D time-harmonic eddy current field of an induction furnace and is compared to other formulations as well. Index terms - Electromagnetic fields, finite element methods, eddy currents, numerical stability, induction heating

This paper presents an improved magnetic field analysis for induction motor models. In the analysis with the conventional numerical modeling of magnetic materials, the vector relations between the flux density and the field intensity under a rotating field can not be expressed exactly. In this paper, we derived the tensor magnetic reluctivity from the data measured with two-dimensional measurement method. This expression is applied to analyze a three-phase induction motor model core. The examples show that the calculated results obtained by our new method are different from those of the conventional modeling. Index terms - induction motor, two-dimensional magnetic properties, finite element method, iron loss, reluctivity tensor

Lately, the three-dimensional (3-D) analog of the Cauchy integral formula was used for several studies in geophysics and magnetism. In this paper, a simple demonstration of the expression of the 3-D analog of the Cauchy integral formula is given using only the usual rules of vector calculus, whereas the demonstrations given in references such as journal papers, treatises, or textbooks require complicated mathematical proceedings and lack clearness. Further on in the paper it is shown that some formulas obtained in references by using the analog of the Cauchy integral formula include inadequate results. The ways to avoid these inadequate results are also shown. Index Terms - Magnetic field computation, three-dimensional Cauchy integral formula

The aim of this paper is to show the advantage of a deterministic global-optimization method in the optimal design of electromechanical actuators. The numerical methods classically used are founded either on nonlinear programming techniques (i.e., augmented Lagrangian, sequential quadratic programming) or on stochastic approaches which are more satisfactorily adapted to global optimum research (i.e., genetic algorithm, simulated annealing). However, the latter methods only guarantee reaching this global optimum with some probability. The present paper proposes a deterministic Branch and Bound algorithm associated with interval arithmetic which is then applied to the dimensioning of a slotless permanent magnet machine. The problem is formulated as a multiobjective-optimization problem with mixed variables. Original and unexpected results in this optimal design are obtained, and comparisons with previous works are presented. Index Terms - Branch and Bound method, electromechanical actuators, global optimization, interval arithmetic, optimal design.

The paper presents the analytic study of an alternated structure of permanent magnets. These structures are used to construct position sensors, for example. Such devices need to be optimized, and only through analytical expressions can this be done. The paper presents these analytical expressions and their use in optimization of the magnetic circuit with regard to such constraints as mechanical airgap and resolution. Index Terms - Analytical calculation, magnetic field, permanent magnet.

In this paper, we study the statistics of zig-zag transition walls in digital magnetic recording and their relationship to transition noise defining quantities. We provide analytic results that link the statistics of zig-zag transitions to media/recording parameters. The basis of our study is the triangle zig-zag transition (TZ-ZT) model due to its well-defined triangle zig-zag shape and its cross-track stability. The results we derive here, however, are of a general nature, and given the right interpretation, apply to other zig-zag models as well, as we show in the paper. We also provide an interpretation of the cross-track correlation width, linking this quantity to the statistics of magnetized clusters in thin-film magnetic media. The paper concludes by showing how these results can be used in media noise modeling.

The purpose of this paper is to determine the mutual inductance between two noncoaxial circular coils. In many cases, such as coil guns or tubular linear motors, one of them is fixed while the other one is moving, and if not supported, its axis may not coincide with that of the fixed coil. This paper presents a method for the calculation of the mutual inductance in the case of noncoaxial coupled coils, the characteristics of this inductance, and experimental results. The computation is based on complete elliptic integrals and on mesh-matrix technique. The method enables one to obtain accurate results from a relatively simple procedure and calculation program. Index Terms - Mutual inductance, noncoaxial coils.

The Advanced Photo System incorporates a magnetic system, using media on the film, which provides the ability to communicate information between system components. This paper presents an overview of: how magnetic recording is utilized by the Advanced Photo System; the difficulties which had to be overcome to incorporate the magnetic system into the film, cameras, and photofinishing equipment; the magnetic data architecture; and introduces the topics contained in the accompanying papers in this session.

Inclusion of both skin and proximity effects in the prediction of impedance matrices in eddy-current problems significantly complicates the prediction of the impedance matrix. In this paper, a technique employing a boundary element method is used to predict these impedance matrices using an additional constant vector potential which is added to the interior of every conductor. This constant vector potential is slightly altered for an axisymmetric problem and allows for the easy prediction of induced voltage in an eddy-current conductor. Perhaps the greatest contribution offered by this paper is in the interpretation of these matrices and in particular, with the negative components comprising the resistance matrix. The phasor diagrams, both for voltage and current as well as magnetic fields, are employed to aid in better understanding the information delivered within the impedance matrix. The explanations are directed specifically toward a three-coil axisymmetric problem. The technique is tested against the measured voltage in a three-phase current fed system. Index Terms - Eddy-current, impedance, matrix, proximity effect.

This paper examines bias, which is the average torque (or current) required to maintain a set actuator position in a disk drive. In this paper, we show that in a disk drive the value of bias depends on several factors including the actuator position, the length of time at the set position, the direction of the actuator motion, the distance traveled by the actuator, the proximity of the set position to locations at which the actuator changed direction, and the proximity of the set position to locations at which the actuator rested. With an adequate prediction of bias, the settling time of a seek can be reduced by properly selecting the initial conditions of the track following controller at the handoff between track seek and track settle. Two prediction algorithms for bias are shown: one based on a series of calibration tests and one based on Dahl's friction model. A method for choosing the initial condition of the integrator of an integral action controller to minimize settling time based on the bias prediction is developed. Index Terms - Disk drives, hysteresis, mechanical factors, modeling, nonlinearities, servo systems.

High-frequency planar magnetic components, employing thin film and thick film technology, have become important components in applications, such as filters and switching converters, due to their ease of manufacture and reliability. In a previous paper, the authors established a frequency dependent impedance formula for planar coils on a magnetic substrate that is infinitely thick. In this paper, two new impedance models are described: the first is for planar coils on a magnetic substrate of finite thickness, and the. second represents a planar coil sandwiched between two substrates. The models include the electrical conductivity of the magnetic material so that the effects of eddy currents, particularly at high frequencies, are taken into account. The eddy currents reduce the inductance and increase the losses associated with the device. The new impedance formulas are derived from Maxwell's equations. Simulations were carried out on a typical device, using finite element analysis, and the results validate the new formulas. This paper establishes the frequency limitations of lossy magnetic substrates. Index Terms - Eddy currents, high-frequency circuits, multilayer inductors, planar magnetics, spiral coils, thick film inductors, thin film inductors.

In this paper, we present a design and optimization procedure which utilizes a case-based approach in design and a response surface methodology, implementing a fractional factorial approach, to determine the empirical models relating the performance of the device and the design parameters. With these models constructed, a genetic algorithm can be used to solve the resulting constrained nonlinear optimization problem quickly to get the optimal device. The main contribution of the paper lies in the effective combination of these three methods.

This paper describes a design procedure that reduces the cogging torque of BLDC motor. This paper proposes that a predefined slot shape on the pole surface reduces the cogging torque. Used are the standard finite elements for field calculation, Maxwell stress tensor for torque, and evolution strategy for optimal design process to determine the slot size. Verified experiment shows that the proposed algorithm reduces the level of mechanical vibration and noise substantially.

The aim of this paper is to show how SMES devices, if arranged with more than two magnetic dipoles, can perform better. The analysis is carried out either considering or not the presence of a ferromagnetic shield. In the latter case a shape optimization of the iron shield is performed using a combined stochastic/deterministic method. The paper shows how advantages can be taken by evaluating the sensitivity matrix of the iron shape optimization by means of a Lagrangian formulation of the Maxwell's equations.

This paper describes an implementation of the static magnetic hysteresis using the finite element method and a vector hysteresis model. In this paper, the vector hysteresis model[1] which is extended from the magnetization - dependent Preisach model is adopted. The magnetization of each element is calculated for a given history of the rotating field. The lagging angle of the magnetization for the applied field is evaluated. It is shown that the magnetization characteristics of the magnetic materials under the rotating field can be explained.

The BIEM coupled with surface impedances gives good results at a low cost for 3D high frequency eddy-currents calculation with linear materials. In this paper, we review the possible extensions to non linear materials. We propose (and test in 3D) an original method, based on ID computations of the complex surface impedance. Results are applied to induction hardening processes. This paper presents essentially validations of the method of non linear surface impedances; a future publication will be devoted to the thermal validation.

In this paper, we report a combined spin-stand measurement and micromagnetic simulation study on narrow track recording characteristics in thin film media. It is found that the onset recording density of nonlinear partial erasure is determined by intertransition percolations near the track edges where the head field gradient is poor. Trimming into the shared pole in merged MR/thin film heads is necessary for performance at both high linear and high track densities. Increasing head field magnitude with respect to medium coercivity increases the width of erase band but not the actual transition track width. When the head is skewed, the edge field overwrites on-track transitions, resulting in a reduction of effective transition track width. The trimming of the shared pole in merged MR/thin film heads can significantly reduce this edge overwrite effect. It is suggested that servo writing schemes should be modified to take into account the phenomena described in this paper.