Areal-Density Capability Measurement Based on 747 Test in Magnetic Recording Systems
A method is presented for determining the areal density (AD) capability of a magnetic recording system based on a set of 747 tests taken over a range of linear densities. By fitting the measured results with a suitable functional form, we can readily predict off-track capability (OTC) at any combination of linear density and track density. Conversely, for a given OTC requirement, we can immediately find the maximum AD that can be reached and the bit aspect ratio required to achieve it. Our results also reveal the effect of skew angle on AD and match well with previous results for perpendicular magnetic recording.
An Off-Track Capability Model Including Noise
An analytical model for off-track capability (OTC) is developed. The model is built on the assumption that, for a given channel, the overall signal to noise ratio (SNR) determines the bit-error-rate (BER). Written magnetization consists of a data track, adjacent tracks and attendant erase bands, and previously written "old information." SNR is determined by the position of the read-back sensor over the medium, and by the characteristic signal, electronic noise, and media noise powers. These parameters are presumed constant for a particular head, disc, and linear density. OTC is determined as the off-track distance beyond which the SNR falls below a given threshold value, which can be correlated to a threshold BER. We compare OTC as predicted by the model to experimental measures of OTC as the track pitch is varied.
An analytical approach to the design of electrodes in high-power, fast-transverse-flow CO2 lasers
Abstract Usually, the design of the electrodes of fast-transverse-flow CO 2 lasers relies more on experimental data than on theoretical analysis. Traditional systems sustain a stable, high-power discharge but the current distribution generates a peaked, non-uniform small-signal-gain pattern. We present a theoretical model suitable for the design of electrodes that achieves a quasi uniform gain distribution. The analysis, based on a two-temperature model and the gas-transport equations, computes the electron density that supports a flat gain pattern. Combining the desired electron density with the electron-balance equations, the model determines the required electric field. The results were used to design a new set of electrodes for a home-made fast transverse flow CO 2 laser. A stable, large volume discharge ( 4 × 8 × 90 cm 3 ) with very good uniformity was obtained. The resulting gain distribution was registered in a bi-dimensional map. The peak gain rose from 1.2 m - 1 , attained with the old electrode set, to 1.6 m - 1 with the new one and the gain showed a homogeneous profile.