Kyaw Sett Myo

Direct Monte Carlo Simulations of Air Bearing Characteristics on Patterned Media

In patterned media recordings such as discrete track and bit-patterned media (BPM) recordings, the presence of pattern structures on the media surface causes the slider air bearing problems more complicated to be analyzed and studied. Using the 3-D direct simulation Monte Carlo (DSMC) method, the plain slider surface and bit/discrete track-patterned disk surface are designed for case studies in this paper. This paper reports the local bearing pressure variations acted on the slider surface due to the air bearing effects of pattern structures on the disk surface using the DSMC method. From the results obtained under the steady-state condition, it is observed that the bearing pressure profiles will be smoother and the bearing forces will approach to a stable value when the pattern pitch values are smaller than 0.4 μm. This critical pitch value is close to 0.3 μm that we reported previously based on modified Reynolds equations. We also investigate the effects of the pattern depth and total recess area ratio on the air bearing characteristics in BPM recording. Furthermore, in order to understand the effect of bit-pattern movements, we simulate the motion of bit-pattern structures by using four typical moving bit-pattern layouts. As of the outcomes, we can conclude that this effect could be negligible if the bit size is in several tens of nanometer scale.

Nonlinear dynamic effects of thermal flying-height control sliders at touch-down

The touch-down test is widely used to calibrate the flying-height (FH) of sliders by gently contacting the disk with the thermal protrusion of thermal FH control (TFC) sliders. However, the dynamic instability of TFC slider during the touch-down may significantly affect the contact detection and FH calibration. This paper highlights the nonlinear dynamics perspectives on the instability of TFC sliders during the touch-down. The mechanism of dynamic instability of TFC sliders is explored by experiments, nonlinear system models and simulations. The impact factors and air bearing surface (ABS) design considerations for minimizing the critical flying-height are also discussed.

Frequency Analyses of Air Bearing Slider in Near Contact and Contact States

Determining the air bearing frequencies is important and essential to understand the complex flying performances of slider. However, in typical flying height test, it is usually difficult to distinguish the air bearing frequencies in the experimental data, especially when the slider is in full flying state. In such a case, it is optional to employ simulation to help determine the air bearing frequencies and their harmonic components. This paper performs both time and frequency domain simulations to analyze air bearing frequencies of a pemto slider and compare the results with experimental data obtained using laser Doppler vibrometer. It is found that the simulation results are well correlated with the experimental results. Time domain simulation provides not only the air bearing frequencies, but also the harmonic frequencies. Frequency domain simulation, on the other hand, provides clear identification of the three dominant air bearing frequencies, with additional information such as air bearing stiffness and damping obtainable. It is suggested that simulations in both time and frequency domains should be conducted to assist in determining the air bearing frequencies and their harmonic components.

A modified slip model for gas lubrication at nanoscale head-disk interface

In this work, we derive a modified slip model for gas lubrication based on the effective viscosity concept and a kinetic-theory-based slip-boundary condition. A more accurate expression for the effective mean-free path is proposed, which can overcome the deficiency of other slip models in predicting effective mean-free path. In comparison with the existing slip models, such as the first, second, and 1.5-order slip models, the current slip model agrees well with F-K model over the entire flow regimes and therefore is expected to be more accurate for ultra-thin gas film lubrication at head-disk interface.

Direct Monte Carlo simulation of nanoscale mixed gas bearings

The conception of sealed hard drives with helium gas mixture has been recently suggested over the current hard drives for achieving higher reliability and less position error. Therefore, it is important to understand the effects of different helium gas mixtures on the slider bearing characteristics in the head–disk interface. In this article, the helium/air and helium/argon gas mixtures are applied as the working fluids and their effects on the bearing characteristics are studied using the direct simulation Monte Carlo method. Based on direct simulation Monte Carlo simulations, the physical properties of these gas mixtures such as mean free path and dynamic viscosity are achieved and compared with those obtained from theoretical models. It is observed that both results are comparable. Using these gas mixture properties, the bearing pressure distributions are calculated under different fractions of helium with conventional molecular gas lubrication models. The outcomes reveal that the molecular gas lubrication results could have relatively good agreement with those of direct simulation Monte Carlo simulations, especially for pure air, helium, or argon gas cases. For gas mixtures, the bearing pressures predicted by molecular gas lubrication model are slightly larger than those from direct simulation Monte Carlo simulation.

Numerical Investigation of Thermal Effects on a HAMR Head-Disk Interface

Heat-assisted magnetic recording (HAMR) is one of prospective high density recording technologies in current hard disk industry. It requires heating a spot on the recording media with the laser beam to overcome the superpara-magnetic limit. The heat produced by laser beam causes the temperature field on the hard disk surface to be highly non-uniform, which may lead to unexpectedly severe lubricant loss, or even the failure of the whole HAMR system. In the meantime, the heat loss caused by the optical delivery system may cause unwanted thermal protrusion on the slider body, which may affect slider’s flying stability in the end.© 2014 ASME

Air Bearing Features on Discrete Track Media

This paper studies the air bearing features on discrete track media by very small mesh size. The mesh size is only 5 nm, and it allows to study the air bearing characteristics of a small square pad flying on discrete track media with sub-micrometer groove pitch. The air bearing spikes and the flying height loss are calculated and discussed. It is observed that the air bearing spikes exist mainly on discrete track media with groove pitches of micrometer level. When the groove pitch is smaller than 0.3 μm, the air bearing cannot “see” the grooves clearly, and the air bearing pressure profile is smooth generally. For groove pitch of micrometer level, the surface with a larger groove pitch provides a stronger air bearing force, if the groove depth and the groove ratio are fixed. For sub-micrometer groove pitches, the air bearing force is approximately independent of the pitch size.