Soo-Choon Kang

A new molecular gas lubrication theory suitable for head-disk interface modeling

A rigorous generalized Reynolds equation, which governs gas lubrication dynamics at the head disk interface (HDI), has been derived from the Bhatnagar–Gross–Krook kinetic equation. Rarefaction effects for arbitrary surface accommodation coefficients are incorporated by calculating both the Couette and Poiseuille flow rates. New flow rate databases have been generated, which correct and extend the erroneous existing databases currently used for HDI simulations. Furthermore, a new set of system equations for the pitch and roll angles has been constructed by including shear stress changes due to rarefaction phenomena, which becomes critically important in estimating slider dynamics at ultralow flying heights.

Multicomponent gas mixture air bearing modeling via lattice Boltzmann method

As the demand for ultrahigh recording density increases, development of an integrated head disk interface (HDI) modeling tool, which considers the air bearing and lubricant film morphology simultaneously is of paramount importance. To overcome the shortcomings of the existing models based on the modified Reynolds equation (MRE), the lattice Boltzmann method (LBM) is a natural choice in modeling high Knudsen number (Kn) flows owing to its advantages over conventional methods. The transient and parallel nature makes this LBM an attractive tool for the next generation air bearing design. Although LBM has been successfully applied to single component systems, a multicomponent system analysis has been thwarted because of the complexity in coupling the terms for each component. Previous studies have shown good results in modeling immiscible component mixtures by use of an interparticle potential. In this paper, we extend our LBM model to predict the flow rate of high Kn pressure-driven flows in multicomponent g...

TRANSIENT RESPONSE OF ULTRALOW FLYING SLIDERS OVER CONTAMINATED AND TEXTURED SURFACES

The transient flying dynamics of positive and negative pressure sliders over nonsmooth surfaces were investigated. Surface roughness was modeled by variously oriented sinusoidal waves, and contaminated surfaces were modeled as series of asperities and pits. A finite element algorithm was used which incorporates a generalized form of the Reynolds equation based upon the linearized Boltzmann equation. A new kinetic equation descriptive of ultralow flying was also discussed. Spectral analysis using fast Fourier transformation was adopted to explore the transient behavior of sliders in the frequency domain.

Image processing techniques for analysis of air bearing surfaces

Numerous studies have shown the importance of surface parameters (i.e., camber, crown, and twist) on air bearing performance. These parameters are used as both modeling inputs and manufacturing controls. Measured values are, however, sensitive to both the assumed shape of the surface (e.g., biquadratic) and the numerical procedures used to extract them from the data (e.g., least squares regression). This sensitivity is becoming even more important as fly heights are reduced below 10 nm. The purpose of this paper is to present the numerical algorithms required to take raw WYKO or ZYGO data of an air bearing surface and automatically convert it into a format that can be used to determine surface parameters or can be directly incorporated into air bearing simulations. The former is useful for determining more accurate representations of the surface, while the latter is useful for determining the impact of these surface approximations.