Paul Davey

Head-disk spacing variation suppression via active flying height control

A novel active flying height control method is proposed for the suppression of head-disk spacing variation in hard disk drives under shock or vibration conditions. The thermal signal detection method is used for real-time derivation of the spacing variation signal for feedback control. Design details of the servo control system are given. Simulation results are provided to demonstrate the effectiveness of the method.

Two-dimensional coding for a multi-track recording system to combat inter-track interference

Increasing track density, through a narrowing of the read head, leads to a reduced signal-to-noise ratio and increased inter-track-interference (ITI). Two-dimensional codes for multi-track recording systems have demonstrated increased capacity over conventional single track run length limited (RLL) codes. This paper describes a two-dimensional code for a multitrack recording system to control ITI by preventing adjacent track transitions. Results show that such a code, when applied to a PRML channel, can significantly improve immunity to crosstalk whilst maintaining a high linear density.

Increased areal density using a 2-dimensional approach

There is a drive toward achieving much higher track density in magnetic recording. Increase in track density will produce more interaction/crosstalk between adjacent tracks. The simulated variation of bit error rate (BER) as a result of increased inter-track interference (ITI) using a Viterbi Detector is presented in this paper. Results show that for a given BER and signal-to-noise ratio (SNR), different levels of ITI can be tolerated depending on the code. Calculations suggest 2-dimensional modulation codes designed for a channel experiencing ITI can result in up to 23% gain in areal density.

Track squeeze using adaptive inter-track interference equalisation

Summary form only given. A new maximum likelihood sequence detection (MLSD) technique to reduce the effects of inter-track interference (ITI) is presented in this paper. As track densities increase, ITI and off-track interference (OTI) occur, and have detrimental effects on the performance of current MLSD decoders. A solution is to perform MLSD with an adaptive ITI equaliser constructed within the decoder trellis.

Two dimensional coding for a multiple-track, maximum-likelihood digital magnetic storage system

Two dimensional run-length-limited (d, k/sub y/) modulation codes were recently introduced as a means of increasing storage capacity in multi-track recording systems. This paper furthers this coding technique by describing a reverse enumeration scheme based on the trellis description of the (d, k/sub y/) constraint for a channel employing extended class IV partial response signalling and maximum likelihood detection. >

Novel Soft-Feedback Equalization Method for Multilevel Magnetic Recording

This paper investigates the use of multilevel modulation for magnetic recording using a novel soft-feedback equalization (SFE) approach. Different aspects of investigation are 1)multilevel recording, 2) SFE, and 3) application of turbo codes. The SFE scheme is a model in which the partial response (PR) equalizer and maximum a posteriori (MAP) decoder are replaced by a linear filter with an iterative MAP decoder. Error correction codes (ECCs) are applied to the multilevel recording system in order to achieve very low error rates. Implementation of the SFE scheme for multilevel recording shows a reduction in complexity in comparison to various PRML schemes. The simulation results show a clear performance gain of multi-level-coded against binary-coded recording systems. At higher signal-to-noise ratio (SNR), the coded multilevel SFE scheme overcomes the error floor effect produced in the coded multilevel PRML scheme, which is caused by minimum distance error events. Overall, this paper proposes the use of coded multilevel recording with SFE scheme at lower rates rather than coded binary recording at higher densities in order to achieve similar performance

Label-Free Sensors Based on Graphene Field-Effect Transistors for the Detection of Human Chorionic Gonadotropin Cancer Risk Biomarker

We report on the development of label-free chemical vapour deposition (CVD) graphene field effect transistor (GFET) immunosensors for the sensitive detection of Human Chorionic Gonadotropin (hCG), a glycoprotein risk biomarker of certain cancers. The GFET sensors were fabricated on Si/SiO2 substrate using photolithography with evaporated chromium and sputtered gold contacts. GFET channels were functionalised with a linker molecule to an immobile anti-hCG antibody on the surface of graphene. The binding reaction of the antibody with varying concentration levels of hCG antigen demonstrated the limit of detection of the GFET sensors to be below 1 pg/mL using four-probe electrical measurements. We also show that annealing can significantly improve the carrier transport properties of GFETs and shift the Dirac point (Fermi level) with reduced p-doping in back-gated measurements. The developed GFET biosensors are generic and could find applications in a broad range of medical diagnostics in addition to cancer, such as neurodegenerative (Alzheimer’s and Parkinson’s) and cardiovascular disorders.

Design of single bidirectional switch single phase rectifier with reduced size DC side capacitor

A single phase rectification technique with a new architecture and control scheme is proposed. The new circuit is constructed by connecting a single bidirectional switch and capacitor in parallel to the diode bridge rectifier. The control strategy is carefully designed to maintain a high input power factor, provide a reduction in the size of the DC side capacitor and reduce the line current harmonics compared with the conventional rectifier. Circuit configuration, design parameters, principles of operation and the mathematical analysis are presented. The AC side harmonics analysis is done using Woodwards notation which applies to chopped waveforms. The proposed concept is verified by the experimental results of a case study.

Using compact disc player optical systems to measure differentially hard disk drive slider and disk motion under hostile conditions

When typical hard disk drives are subjected to vibration, data transfer failure was found to be particularly significant at frequencies between 450 and 700 Hz At non-critical frequencies of vibration the typical hard disk drive is capable of reliably transferring data whilst subjected to as much as 45 g of vibration. However, between 450 and 700 Hz they typically fail to transfer data at as little as 1 g. These data failures can be attributed to two key components: the suspension arm and the hard disk. An optical system, based on CD-ROM optics, has been developed to unobtrusively measure disk flutter and flying height variations, and to validate measurements made using PVdF sensors.

Pulse slimming in magnetic recording using digital signal processing techniques

Abstract An equalisation method for reducing peak shift caused by inter-symbol interference in high density digital magnetic recording is presented. A TMS320C25 Digital Signal Processor has been applied to a low cost digital magnetic recording system. Software is used to slim the signal from the read head to produce a 30% slimmer pulse width. This is translated into a comparable data rate gain at the same error rate.