ANALYTICAL INVESTIGATIONS IN MAGNETIC RECORDING

The Fourier method is used to provide new analytic solutions for idealized mathematical models of double-element shielded magnetoresistive (MR) recording heads. The general two-dimensional model allows analysis of various recording head configurations; a single pole head, a ring head, a dual stripe head and a differential head. The analysis accommodates both longitudinal recording (with no soft magnetic underlayer present) and perpendicular recording (in the presence of a soft underlayer). Typical field, spectral response function and output voltage pulse plots for double-element MR heads are given and compared to published, approximate solutions. The integrals arising in the determination of the Fourier series coefficients, magnetic potential and magnetic field components are expressed either as rapidly convergent infinite series or in terms of special functions to provide a more efficient means of evaluation than numerical integration. It is shown that, in many situations, it is only necessary to take the first Fourier coefficient in the calculation of output voltage pulse shapes in order to achieve sufficiently accurate results. Bi-variate regression techniques are used to provide a convenient method to approximate the first Fourier series coefficient for a broad range of typical head dimensions. The thesis goes on to examine high speed switching behaviour in two classes of recording media by considering two different particle orientation distributions; 2D random media - intended to simulate a modern thin film rigid disk, and 3D oriented media- simulating a single domain particulate tape media. The gyromagnetic switching constant of a medium is calculated directly from the Landau - Lifshitz - Gilbert (L-L-G) equation of motion, which is solved numerically. The switching constants produced are discussed and compared with published experimental values for different media

Mathematical Analysis of Novel Magnetic Recording Heads

As a contribution to increasing the areal density of digital data stored on a magnetic recording medium, this thesis provides mathematical analyses of various magnetic recording heads. Each of the heads considered here is for use in a perpendicular recording system, writing to or reading from a multi-layer medium which includes a high magnetic permeability layer between the data storage layer and the substrate. The exact two-dimensional analysis is performed in each case by one of two methods: either Fourier analysis or conformal mapping. The types of heads analysed include conventional styles but particular emphasis is placed on the effects of the novel idea of potential grading across the pole pieces. Exact head fields are derived for thin film heads with both constant and linearly varying pole potentials, single pole heads with linearly and arbitrarily varying pole potentials and shielded magnetoresistive heads, all in the presence of a magnetic underlayer. These and other published solutions are used to derive output characteristics for perpendicular replay heads, which are compared with published theoretical and experimental results where possible. The Fourier solutions obtained are in the form of infinite series dependent on at least one set of coefficients which are determined by infinite systems of linear equations. Approximations to the potentials in the head face planes, independent of these coefficients, are derived from the exact Fourier solutions. The accuracy of these approximations is demonstrated when they are used to estimate the vertical field components and the spectral response functions. Heads with graded pole potentials are found to have more localised vertical field components than the corresponding constant potential heads. They are also better suited for use with thin media for 'in contact' recording

Broadband point measurement of transient magnetic interference in substations with magnetoresistive sensors

This journal issue contain selected papers from the Asia-Pacific Data Storage Conference (APDSC'13)Electromagnetic interference (EMI) in substations can be an obstacle for the development of the Smart Grid. This challenge is particularly critical since more and more secondary systems are transferred from control rooms to switching yards in modern power systems. Thus, it is important to develop a tool that can properly characterize and evaluate the EMI level. This paper introduces a novel broadband point measurement technology for evaluating the effect of transient magnetic field (TMF) on secondary systems in substations. The received disturbance level is defined for the victim circuit and the evaluation approach is proposed. The effect of sensor size on the measurement of TMF is explained and illustrated with numerical simulation, indicating the importance of point measurement. The designed measurement system was tested and the TMF caused by charging traveling wave in a 110-kV substation was characterized. Our results show that the TMF may produce significant effect on the secondary systems in a substation, and thus it is important to have the capability to evaluate the interference level.published_or_final_versio

A Three-Dimensional Singular Model of a Magnetic Perpendicular Recording Head with Applications to Inter-Track Interference

Two-dimensional models of the read head are not suitable for simulating the replay of the extremely high density data that is expected to be achieved in hard drives using perpendicular recording. By matching a singular function approximation to the Fourier solution at the air-bearing surface (ABS), a three-dimensional analytic model of a shielded giant magnetoresistive head, with side shields, for perpendicular replay is derived in this thesis. An explicit expression for the potential in the ABS is presented and parameters in that expression are accurately estimated for a range of practical head dimensions. Using only a few terms of this singular potential model, the vertical field is accurate to within 2% of the sensor potential in the region of the medium for the majority of head dimensions suitable for magnetic recording. The expected increase in areal density in hard drives using perpendicular technology will require very narrow t racks which normally suffer from large inter-track interference (ITI) or crosstalk. This interference can corrupt the read data and reduce t he signal strength. Here, the effects of ITI across three tracks in a three-head system are modelled by applying the three-dimensional singular function model of the head field. The magnetisation patterns which cause the worst ITI are identified so that these codes can be prohibited. A coding constraints scheme, in which ITI is exploited to read from tracks which have widths that are just 70% of the width of the head, is presented

Sensors and Methods for Railway Signalling Equipment Monitoring

Signalling upgrade projects that have been installed in equipment rooms in the recent past have limited capability to monitor performance of certain types of external circuits. To modify the equipment rooms on the commissioned railway would prove very expensive to implement and would be unacceptable in terms of delays caused to passenger services due to re-commissioning circuits after modification, to comply with rail signalling standards. The use of magnetoresistive sensors to provide performance data on point circuit operation and point operation is investigated. The sensors are bench tested on their ability to measure current in a circuit in a non-intrusive manner. The effect of shielding on the sensor performance is tested and found to be significant. The response of the sensors with various levels of amplification produces linear responses across a range of circuit gain. The output of the sensor circuit is demonstrated for various periods of interruption of conductor current. A three-axis accelerometer is mounted on a linear actuator to demonstrate the type of output expected from similar sensors mounted on a set of points. Measurements of current in point detection circuits and acceleration forces resulting from vibration of out of tolerance mechanical assemblies can provide valuable information on performance and possible threats to safe operation of equipment. The sensors seem capable of measuring the current in a conductor with a comparatively high degree of sensitivity. There is development work required on shielding the sensor from magnetic fields other than those being measured. The accelerometer work is at a demonstration level and requires development. The future testing work with accelerometers should be at a facility where multiple point moves can be made; with the capability to introduce faults to the point mechanisms. Methods can then be developed for analysis of the vibration signatures produced by the various faults

Advanced Magnetic Thin-Film Heads Under Read-While-Write Operation

A Read-While-Write (RWW) operation for tape and/or potentially disk applications is needed in the following three cases: 1. High reliability; 2. Data servo systems; 3. Buried servo systems. All these applications mean that the read (servo) head and write head are operative simultaneously. Consequently, RWW operation will require work to suppress the so-called crossfeed field radiation from the write head. Traditionally, write-read crossfeed has been reduced in conventional magnetic recording heads by a variety of screening methods, but the effectness of these methods is very limited. On the other hand, the early theoretical investigations of the crossfeed problem concentrating on the flux line pattern in front of a head structure based on a simplified model, may not be comprehensive. Today a growing number of magnetic recording equipment manufacturers employ thin-film technology to fabricate heads and thereby the size of the modern head is much smaller than in the past. The increasing use of thin-film metallic magnetic materials for heads, along with the appearance of other new technologies, such as the MR reproductive mode and keepered media, has stimulated the need for an increased understanding of the crossfeed problem by advanced analysis methods and a satisfactory practical solution to achieve the RWW operation. The work described in this thesis to suppress the crossfeed field involves both a novel reproductive mode of a Dual Magnetoresistive (DMR) head, which was originally designed to gain a large reproduce sensitivity at high linear recording densities exceeding 100 kFCI, playing the key role in suppressing the crossfeed (the corresponding signal-noise ratio is over 38 dB), and several other compensation schemes, giving further suppression. Advanced analytical and numerical methods of estimating crossfeed in single and multi track thin-film/MR heads under both DC and AC excitations can often help a head designer understand how the crossfeed field spreads and therefore how to suppress the crossfeed field from the standpoint of an overall head configuration. This work also assesses the scale of the crossfeed problem by making measurements on current and improved heads, thereby adapting the main contributors to crossfeed. The relevance of this work to the computer industry is clear for achieving simultaneous operation of the read head and write head, especially in a thin-film head assembly. This is because computer data rates must increase to meet the demands of storing more and more information in less time as computer graphics packages become more sophisticated.Hewlett Packar

Design and development of a multipurpose, boresighted star tracker

Design and development of boresighted star tracke

Medium magnetizations for longitudinal high-density digital recordings

©2003 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.This paper reports on the influences of magnetic media remanent magnetizations on the output levels in digital magnetic tape and disk recording. While at low densities a high magnetization is required for a high output, a lower magnetization is required at high densities. However, for particular applications, an output near to the maximum can be obtained from a wide range of remanent magnetization values, which suggests possible uses for media with diverse properties

A Novel Approach for Fault Location of Overhead Transmission Line with Non-Contact Magnetic Field Measurement

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