The Influence of Bit Patterned Medium Design and Imperfections on Magnetoresistive Playback

Magnetoresistive playback off bit patterned magnetic recording media is studied. Three playback configurations are compared: not shielded sensors, shielded sensors commonly used in magnetic recording systems, and shielded differential sensors. Influence of patterned medium parameters including bit-filling ratio, bit shape, bit position jitter, bit-size variation on the playback signal is studied. Playback signal amplitude, D50, and signal-to-noise ratio are used to compare different playback sensor configurations. It is found that in general, shielded differential readers offer superior performance as compared to both shielded single sensor readers and not shielded readers.     

Magnetic recording at video cassette recorder for home use

A 2-head helical scan type, home-use video cassette recorder was developed and this new system was named "VHS". The basic tape pattern enables variable speed playback, permitting noise-free still-frame and double-speed playback. For equipment built to the NTSC standard, to attain high-density recording, various techniques including a 90° phase-shift color signal processing technique, double limiter circuit and burst signal emphasis circuit were employed. An adequate color signal processing method was developed for the PAL and SECAM television standards.     

Density improvements in digital magnetic recording by decision feedback equalization

The information density improvements are estimated that are feasible by applying decision feedback equalization instead of conventional linear equalization in digital magnetic recording systems, with differentiating playback heads. Significant improvements are shown to be within reach for an important class of transmission codes.     

Wavelength response of harmonic distortion in AC-bias recording

Wavelength response of harmonic distortion in ac-bias recording is analyzed. The wavelength response is affected in both the record and playback processes. In the record process tape nonlinearity and magnetization phase shift, which is dependent on signal-field intensity, are taken into account. In the playback process, tape thickness, tape-to-head spacing, gap length, etc. axe taken into account. An approximate expression for the third-harmonic distortion is derived. The experimental data show quantitative agreement with theory.     

BEM analysis of spectral response from finite pole-length heads on perpendicular media

The Boundary Element Method (BEM) is used to solve for the fields from high-permeability, finite pole-tip gapped heads, with and without a permeable layer beneath the recording medium. The underlayer enhances the recording and playback performance for perpendicular magnetization by increasing both perpendicular fields and field gradients. Reciprocity is used to find the spectral (frequency) response for both sine-wave and square-wave perpendicular magnetizations. Regions of low spectral response, geometrically induced by the finite pole-tips, are more pronounced with the underlayer than without, and are explored for various pole-lengths.     

Theory of playback process with soft magnetic underlayer

Based on the Tsuboi-Fushida-Wallace spacing loss law, reciprocity principle, and the principle of an image plane, a two-dimensional, head independent theory of the playback process has been developed for perpendicular magnetic recording (PMR) media with a soft magnetic underlayer (SMUL). An assumption that the reversible magnetic permeability of the recording media is equal to one gives results in a simple form. The article, while not addressing the effect of underlayer on write performances, demonstrates complications caused by the presence of the underlayer during readback.     

Signal processing and a groove baseband recording method to achieve a high-density optical disc

We propose a method for recording a multilevel signal onto optical read-only-memory discs. In this method we use signal processing to generate a multilevel recording signal that satisfies the zero-intersymbol interference condition and the zero-dc condition. The resultant multilevel signal is emboss recorded as the position displacement of groove walls. To play back a disc, push-pull detection and an adaptive equalizer are used. We also introduce feedback to reduce the nonlinear characteristics existing in the recording and playback systems. An experimental disc with 0.6-mum track pitch and 0.28-mum/bit density is made. When a digital versatile disc equivalent optical pickup is used to play back this disc, we confirm that a two-dimensional eye pattern of 16 levels is clearly observed.     

Holographic zone plates for f x theta and collimating lenses

A holographic zone plate generated by subtracting the spherical wave phase is proposed, that is, a hologram generated by using two divergent or convergent spherical waves. This holographic zone plate can correct the increase in focal power in a radial direction in contrast with the interferometric zone plate. Use of this holographic zone plate for f x O and collimating lenses is analyzed. For an f x O lens, it is shown that an optimum combination of recording spherical waves exists that satisfies both scan linearity and image field flatness. For a collimating lens for a laser diode, it is shown that aberration can be corrected for different playback wavelengths from that used during recording.     

An experimental digital VCR for consumer use

An experimental digital VCR (DVCR hereinafter) was developed. The DVCR has two new technologies for reduction of tape consumption. One is a bit rate reduction technology of a component video signal down to around 25 Mbps and the other is a high density recording technology. The bit rate reduction technology is based on an 8×8/2×4×8 two dimensional DCT (Discrete Cosine Transform) and a VLC (Variable Length Coding) that completes over 5 macro blocks. Editing, trick plays and invisible error concealments also have been realized by this bit rate reduction while keeping the playback picture quality very high. The high density recording technology is based on ME tape and an ATF (Automatic Track Finding) system. A track pitch of 10 μm and a bit length on tape of 0.25 μm have been realized. The possibility of a higher linear recording density has been confirmed through theoretical analysis, simulations and experiments     

Not just another self-consistent magnetic recording model

A self-consistent magnetic recording modeling method is presented which has proven useful in recording channel design on thin media. Improvements in the magnetic model and in the mathematical treatment stabilize the iterative process and reduce computer storage requirements. Major and minor media loops are fitted to quickly computable bipolynomials. Mathematical improvements include using a strong band diagonal demagnetization matrix, analytic integration with quadratic magnetization fitting, and Newton-Raphson iteration, which gives rapid convergence without underrelaxation. Quantitative predictions of timing errors in 16-bit modified frequency modulation (MFM) data patterns on a 350-bit/mm, 20-track/mm disk memory are presented, as well as playback amplitudes and saturation currents. Predictions can also be compared with experimental read/write data to determine system parameters. Two examples are given: the inference of the head efficiency and of the effective high-frequency medium squareness.     

Wear-resistant magnetic head using amorphous alloy material

An audio recording/playback head using an amorphous (Fe-Co-Ru-Cr) ₇₅(Si-B)₂₅ alloy was developed. Compared with a commercial Sendust head, three excellent features were observed. The wear of the amorphous alloy head when used with γ-Fe₂O ₃ is two-thirds that of the Sendust head. The output level at high-frequency (14 kHz) is 5 dB higher than that of the Sendust head. The bias current for the amorphous alloy head is half that of the Sendust head     

Study of Lithographically Defined Data Track and Servo Patterns

We report on fabrication of discrete tracks on perpendicular magnetic recording (PMR) media with an e-beam lithographical process. We studied the recording performance of the e-beam media on a spinstand in parallel with conventional PMR media. Discrete track media show significant reduction in adjacent track erasure (ATE). We studied and quantitatively measured the source of the ATE improvement, and developed a triple track geometrical model to calculate achievable track density for both discrete track recording (DTR) and continuous media. From the model, we identify two factors of DTR that contribute to reaching a higher TPI. Using the same fabrication technique, we also studied servo burst design and its playback waveform quality. At 250 ktpi, we compare DTR servo bursts with servo bursts written with a conventional method. DTR servo bursts show better edge definition, which can translate to better position error signal sensitivity and support higher TPI in the future.Discrete tracks are fabricated on conventional PMR media with an e-beam litho graphical process. The recording performance is studied on a spinstand in parallel with conventional PMR media. Discrete track media shows significant reduction in adjacent track erasure (ATE). The source of the ATE improvement is studied and quantitatively measured. A triple track geometrical model is developed to calculate achievable track density for both DTR and continuous media. From the model, we identify two factors of DTR, which contribute to reaching a higher TPI. Using the same fabrication technique, we also study servo burst design and its playback waveform quality. At 250 ktpi, we compare DTR servo bursts and servo bursts written with a conventional method. DTR servo bursts show better edge definition, which can translate to better PES signal sensitivity and support higher TPI in the future.     

Time-based approach to obtain quantitative measures for ergonomics hazard analysis

The paper describes a methodology for conducting an ergonomic analysis that allows ergonomists to gather data while off site. The analysis described is carried out on portable computing devices, using common computer applications. It includes data collection via a camera on the manufacturing floor and conversion into a digital format. Software is suggested for playback and semi-automatic work sampling of work cycles while recording observations to electronic form, to generate rapidly the analysis of results. Snapshot observations are made on frozen video frames that are categorized into work elements, upper body joint posture and static/dynamic effort. Using two case studies, it is shown how the approach may be implemented as a procedure of choice to complete a quantitative work analysis.     

Micromagnetic recording model of pole-tip saturation effects

Auxiliary write-head fields, either from simple analytic approximations or from finite-element computations, are used to record transitions on a Landau-Lifschitz-Gilbert model of thin-film recording media. A micromagnetic model of a magnetoresistive element is used to read back the transitions. Focus is on the impact of pole-tip saturation on the quality of the recorded track and subsequent playback. It is shown that with increasing write current, the quality of the recorded transitions degrades much more rapidly than would be expected from the analytical expressions for the write-head field. Specifically, head saturation causes the transition parameter to increase. At high write currents, poor write field gradients at the track edges result in a strong increase in transition parameter with read width percentage of the recorded track     

Experimental studies of longitudinal and perpendicular high density recording

Single layer and double layer Co-Cr disks of various coercivities were sputter-deposited on rigid substrates and magnetic parameters measured. Record and playback properties were studied using both ferrite and thin film heads under identical system environments. A well optimized Ni-Co plated longitudinal disk was used as a benchmark throughout this investigation for direct comparison. With the objective of using "off the shelf" ring heads to bring up the perpendicular recording technology on rigid substrates, it was found that the performance of both our preliminary single and double layer Co-Cr perpendicular disks were at least as good as the well optimized longitudinal disk. The double layer disks have an added advantage of lower write current. Signal processing via Hilbert transform using both rectangular and Hamming windows was also studied and applied to the output waveforms.     

The helical-scan magnetic tape recorder as a digital communication channel

The properties of a magnetic tape recorder are viewed in terms of a digital magnetic recording/playback channel which exhibits fading (reduction of playback-signal level) and nonlinear behavior. A method is presented whereby channel nonlinearity may be quantified in a format useful for signal and receiver design. Measurements show this nonlinearity to be relatively small for symmetric two-level signals. Deep fades (dropouts) are the most significant source of errors in digital tape recordings. Fading is considered as multiplicative noise on an essentially linear channel, and measurements are made of the fade probability distribution and an associated additional time dispersion. While the fading process appears to occur relatively slowly (compared with the bit period), neither its probability distribution nor its associated dispersion encourage the use of a receiver which is able to adapt to the changing channel characteristics. Finally an attempt is made to ascribe the fading process to repeatable variations in head-tape separation, and a corresponding probability distribution for this separation is obtained. A helical-scan video recorder was used throughout the measurements because of its low cost and its potential as a high-density storage facility.     

Transition Curvature Assessment for High TPI Applications

Transition curvature is a growing concern for high tracks per inch application. Due to low resolution from the playback transducer in cross track direction, the characterization of the transition edge is very difficult. This situation increases the engineering difficulty for writer pole design optimization and recording performance analysis. We have derived a simple transition shape model to study the transition curvature quantitatively. The complicated transition edge is simplified into one curving parameter. With such simplification, we are able to relate the transition curving effect with the cross track profile. In this paper, we will discuss the concept and analytical derivation of this model. A particular H/M combination is studied and its transition curvature is estimated. Compared with magnetic force microscope and micromagnetic modeling, this new approach has potential to become a practical spinstand or even Hard disk drive measurement if the W/R nonlinear effects are minimized.     

嵌入式智能音乐播放系统的设计与实现

针对目前音乐播放系统的空间和时间受限问题,设计并实现了一种基于移动端的智能音乐播放系统。该系统由移动端软件APP和服务端两部分构成,服务端包括路由器、智能网络机顶盒和音响设备,具备定时播放和移动端实时控制播放的功能。该系统是采用基于STUN(Simple Traversal of User Datagram Protocol over NATs)的网络地址转换(Network Address Translation,NAT)穿透方式的远程控制以及家庭电视网络机顶盒来实现的。它不仅可以实现家庭音响的定时播放,还能通过移动端来远程控制音乐的播放。此外,可以实现歌曲的远程更新和歌曲播放时间的随意控制及更改。实验结果表明,该系统效果良好,具有广阔的应用前景及商业价值,可应用于家庭、商场、学校等有特定需求的环境。文章以家庭音乐播放系统为例进行设计说明。     

Delivery of pre‐stored videos for mobile clients with insufficient playback buffer and bounded delay guarantee

Abstract

A deterministic service model assisted by a sufficiently large playback buffer space can provide bounded delay guarantees for video packets and simplify network resource management. However, many popular mobile terminals do not have sufficient memory capacity for deterministic video services since the embedded memory is limited and needs to be shared by numerous software programs and masses of personal data. This paper improves the traditional deterministic modeling approach for delivering pre‐stored videos to mobile clients with QoS guarantees. The limitation of playback buffer space, the network delay jitter, the processing load of resource management, and the QoS guarantee are considered in the proposed mechanism. Some traffic smoothing operations are integrated into the proposed mechanism for reducing the playback buffer demand and data rate variation. This paper further proposes a smart video frame skip algorithm, originating at the sender for preventing possible overflow problems due to insufficient playback buffer space. The algorithm can determine the most suitable temporal range for skipping frames and prevent arbitrary discarding from inappropriate video frames such as I‐frames on the client side. Simulation results reveal that the proposed mechanism can effectively remedy situations of insufficient playback buffer space while still maintaining the advantages of deterministic services.     

The effect of MR head geometry on playback pulse shape and spectra

The playback properties and spectra of a shielded magnetoresistive head are examined utilizing a Fourier series method. Semi-analytic solutions are given for the magnetic scalar potential and spectra in terms of coefficients which have been numerically determined for common geometries. Voltage pulses are generated by convolving the potential with the derivative of a tanh longitudinal magnetization transition. Expressions for the PW₅₀ versus flying height are obtained by fitting the widths of the theoretically determined playback pulses. It is found that the playback properties of a shielded magnetoresistive head depend strongly on the geometry