Yoke Thickness Research Articles

Flattop-Type Writer Using Soft Magnetic Films with High Resistivity

To improve write performance at high frequency, a flattop-type head consisting of a flat upper yoke and sputtered soft magnetic films is proposed. The sputteredFeAlO films used as yoke materials are magnetically soft, and have a resistivityρ of -100 μΩcm, a saturation magnetic flux density Bs of -1.8T, and an anisotropy field Hk of -25 Oe. All of these values for the FeAlO films are higher than those of conventional plated NiFe yoke materials. The yoke thickness and length are 2μm and 18μm, respectively. A flattop-type head containing an FeAlO yoke at a high writing frequency of more than 540 Mfrps has an O/W of around -30 dB and shows good NLTS (≤15%). Consequently, the improvement of the write performance at high frequency is confirmed when plated 45-50 NiFe films are replaced by sputtered FeAlO films as yoke materials.

Precision septum-like dipole magnet for the HERA luminosity upgrade

Within the framework of the HERA luminosity upgrade project Scanditronix Magnet AB has designed in collaboration with AMACC AB, IBA S.A. and DESY a septum-like dipole for the compensation of orbit differences between e/sup +/-p and e~-p collisions at HERA. The magnet yoke is 640 mm long, 415 mm wide and 550 mm high. The total magnet length is 930 mm. The pole distance is 70 mm, the "good field" region is /spl plusmn/ 20 mm centered around the nominal proton orbit. To meet the high field quality requirements for the whole range of field excitation between 0.1 T and 1.1 T VACOFLUX shims have been added to the pole edges to reduce saturation effects. The air gap is extended from the pole region by 235 mm to allow incoming synchrotron radiation light to pass through the magnet without being scattered. The separation between proton and electron beam at the magnet position at 18.88 m away from the interaction point is 121 mm. Carefully chosen thickness of the return yoke, a 13 mm thick shielding plate between proton and electron beam and 40 mm thick mirror plates on the front faces of the magnet reduce the field outside the magnet well below the tolerable value of 0,5/sub */10/sup -3/ T/sub */m integrated along the e-orbit.

Understanding single-turn write head design at narrow track widths

This paper provides a systematic micromagnetic analysis on the magnetization processes-in various miniaturized single-turn head designs. The calculation results show that a thick yoke yields the formation of a magnetization vortex through the yoke thickness, resulting in efficient flux conduction at small yoke dimensions. A vortex structure is also important for the pole tips to maintain zero remanence after writing. Following this understanding, a hollow yoke structure has been studied to promote the efficient flux conduction in the yoke and flux closure mode in the pole tips at the remanent state. The simulation results are elucidating for efficient single-turn head designs at small yoke dimensions.

Influence of power converter on induction motor acoustic noise: interaction between control strategy and mechanical structure

A general method for reducing noise due to the coupling of an electric machine and a power converter is presented. This problem is generally broken down into three parts: machine design, switch control and mechanical structure response. This may involve the use of numerical methods, which require much computation, and is not well suited to the analysis of the complete drive. The method presented is semianalytical and based on rotating field theory, while the fast Fourier transform permits a global approach to the problem. This method may be used at the design stage of the electric machine (slot number, slot aperture, stator yoke thickness) or for the choice of PWM strategy and parameters for the power converter. The theory is illustrated by experimental results based on a 700 W induction motor associated with a natural sampling power converter. Acoustic measurements, made in a semianechoic room, show that minor modifications of the PWM control strategy greatly improve acoustic performance.

Investigation of Adhesively Bonded Joints for Composite Propeller Shafts

Substituting composite structures for conventional metallic structures has many advantages because of higher specific stiffness and specific strength of composite materials. In this work, one-piece propeller shafts composed of carbon/epoxy composites were designed and manufactured for a rear wheel drive automobile satisfying three design specifications, such as static torque transmission capability, torsional buckling and the fundamental natural bending frequency. Single lap adhesively bonded joint was used to join the composite shaft and the aluminum yoke. The torque transmission capability of the adhesively bonded composite shaft was calculated with respect to bonding length and yoke thickness by finite element method and compared with the experimental result. Torque transmission capability was based on the Tsai-Wu failure index for composite shaft and the failure model which incorporated the nonlinear mechanical behavior of aluminum yoke and epoxy adhesive. From the experiments and FEM analyses, it was found that the static torque transmission capability of the composite propeller shaft was highest at the critical yoke thickness, and saturated beyond the critical length. Also, it was found that the one-piece composite propeller shaft had 40% weight saving effect compared with a conventional two-piece steel propeller shaft.

Torques and yoke thickness for Switched Reluctance Motor

A Switched Reluctance Motor has a doubly salient structure, both stator and rotor have saliency and it has an advantage in a harsh environments due to a simple and robust structure. There are two winding methods, the one is fully pitched winding and other is short pitched winding. A fully pitched winding of Switched Reluctance Motor has a number of different current-excitation patterns such as unipolar and bipolar. Its winding configuration results in more efficient use of the electric circuit, with each phase contributing to torque for more than half of the cycle of rotation. Therefore, for many machine configurations significantly greater torques are predicted for a given frame size. But output torques depend on the yoke thickness. This paper examines the output torques for the different yoke thickness and different current-excitation by the experimental and analytical results using the two dimensional finite element method. As a result, the torque performance of fully pitched winding SRM driven by the bipolar excitation is extremely affected with the yoke thickness.

Influence of stator geometry upon vibratory behaviour and electromagnetic performances of switched reluctance motors

The vibrations and the acoustic noise produced by switched reluctance motors (SRMs) are linked to current wave form and to their structural properties. The authors carried out a parametric study to quantify the influence of the stator geometry upon vibratory behaviour of a 6/4 SRM. Their study shows the important influence of stator yoke thickness on vibration reduction compared to the other stator shape parameters. Moreover, a less noisy structure is proposed, based on the simultaneous analysis of electromagnetic performances and elastic characteristics.

Simulation study of the magnetic coupling between radial magnetic gears

The torque of magnetic coupling with different magnetic poles has been investigated by theoretical computations with two dimensional modeling processes of finite element analysis. The torque is sensitive to the number of magnetic poles, the material of the magnetic gears, and the distance between the magnetic gears. For a 2 mm separation distance of two magnetic gears with 20 mm radius, the maximum torque occurs between 6 and 20 poles which is dependent on the thickness of the iron yoke inside the magnets, and on the magnetization configuration within a pole of the magnets. This is explained by analyzing the magnetic coupling strength of each pole. Finally, the computer calculation is tested using an experimental data taken from a sintered NdFeB magnetic gear.

High frequency head and playback model for thin-film recording heads

A thin-film head field and readback model that allows for eddy currents has been proposed and used to compute complex head efficiency, inductance, anomalous (ac) resistance, head saturation fields and locations, as well as the digital playback parametrics high and low frequency amplitude, resolution, PW-50, and maximum overwrite fields with a fair amount of accuracy. The head model solves for the time-dependent vector potential in a geometry that closely resembles a modern three dimensional thin-film recording head, including variable pole and yoke width, thickness, permeability, resistivity, neck angle and other geometrical parameters. Readback emulation is done with a discrete Fourier version of the reciprocity integral using Szczech fields and arctan transitions, along with complex efficiencies from the head model. Detailed comparisons with experimental observations are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electroplated CoNiFe alloy for use in an integrated inductive magnetoresistive recording head

An electrodeposition formula and operating conditions were developed and optimized for the high saturation magnetization Co80Ni10Fe10 alloy. The effects of magnetic field application during deposition and in subsequent process operations was investigated. The bulk film magnetic performance was compared to conventional Permalloy. Identical write heads, designed for a 300 Mbit/in.2 operating point, were fabricated and tested for a direct comparison of conventional NiFe and CoNiFe. The yoke thickness of the CoNiFe heads was scaled linearly by the difference in saturation moment. Overwrite performance on high coercivity media demonstrated that the CoNiFe heads performance was equivalent to the thicker NiFe heads. Heads fabricated with yokes deposited in an orthogonal switching field, annealed with no applied field, exhibited reduced Hk in the bulk film measurement and reduced saturation write currents. The addition of boron to the alloy reduced coercivity.

Monte Carlo simulation of thin film head read-write performance

Read-write simulations of thin-film head longitudinal recording performance with thin-film disks are described. Acceptable electrical performance of thin-film heads depends on tight control of numerous parameters, and Monte Carlo simulation is used to quantify read-write sensitivity to head variations and to identify the critical parameters. A population of similar heads is assumed, and ten head parameters are subjected to random variations. The resultant electrical performance is dominated by head-disk spacing, with throat height, gap length, trackwidth, and pole thickness following in order of importance. Reasonable variations in coil resistance insulation thickness, yoke thickness, magnetic permeability, or inductance show relatively little influence on recording performance. >

Fabrication process for high track density yoke MR heads

A fabrication process was developed for a high track density yoke MR (magnetoresistive) head whose track width is determined by its front yoke thickness. The fabrication process, involving planarized front yoke formation, consists of the deposition process for a grooved yoke pattern with vertical side wall and a subsequent etch-back process with polystyrene polymer. Extraordinary recessed patterns, 3.5- mu m deep, were almost completely planarized to less than 0.1 mu m using these processes. Fabricated pattern-evaluation results indicate that CoZr system films are more suitable for use as a yoke material than NiFe films. Microstructure analyses reveal that the degradation in fabricated NiFe patterns is related to the structural change at the region near the grooved pattern side wall.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A yoke magnetoresistive head for high track density recording

For high track density magnetic recording, a new yoke MR head, which has two kinds of yoke elements and center-tapped differential MR elements, has been developed. The track width(2.7μm)of the head is determined by its yoke thickness. Magnetic anisotropy control of the yoke elements and differential MR elements configuration provide low noise and high sensitivity. Output voltage 40μV p-p /μm at 25 FRPM and less than -30dB second harmonic distortion were obtained for 3μm recorded track width. Further, C/N values, which is the signal to noise ratio measured with a 10kHz bandwidth, increased by 3dB with differential MR elements configuration. This head has the potential to achieve high track density recording.

Analysis of the outer electromagnetic shield of a superconducting turbine-generator

With reference to a superconductive synchronous generator the iron losses in the outer shield are evaluated, using the vector potential algorithm and the Poisson-like equation. The numerical results are compared with those obtained by means of a finite elements program. The temperature distribution in the shield is also determined. The thickness of the iron yoke is then optimized introducing another conductive cylinder outside it. The optimization is done with reference to the overall Joule losses in the shielding system.