Sub-mm disk waviness characteristics and slider flying dynamics under thermal FH control

The flying dynamics and flying stability of a slider are the key issues at sub-5 nm flying height (FH) under thermal FH control. The resonant frequencies of current sliders are at 100 kHz level. At present linear disk velocities, the disk waviness at sub-mm level and 10 micron level can excite the resonant modes of the slider and induce FH modulation. This work uses the triple-harmonic method to monitor the dynamic FH signal during the process of thermal FH control. As the FH reduces, the same disk waviness characteristics excite larger dynamic FH modulation.     

基于强度干涉原理的双光路动态测量方法

在近场光存储方案中,头盘间距动态测控技术是近场光存储理论和技术的实用化。根据近场光学头的飞行特点,提出了一种基于光强干涉原理的测量系统,重点介绍了其测量原理和标定方法。采用双光路结构来提高测量分辨率,利用光偏振特性来消除反馈光对信号光的干扰。通过对系统性能的分析和试验表明,动态特性达到了500kHz,测量分辨率高于1nm,可满足系统高精度动态测试的要求。     

基于多物理场的TFC磁头热传导机理及其影响因素仿真研究

为了利用微尺度热效应的热致飞高控制(TFC)磁头技术实现磁头飞行高度的精确控制,分析了工作状态下TFC滑块在多物理场综合作用下所呈现出来的传热特性及其主要影响因素,考虑了磁头磁盘间超薄气膜的稀薄效应,建立滑块导热、空气轴承表面传热、气膜流动等模型,利用有限元法,对磁头热变形作用机理及热传导特性对滑块动力学特性影响进行了仿真研究,结果表明,建立的传热模型及对雷诺方程的修正适用于求解磁头磁盘界面气膜传热问题和磁头滑块的动力学问题;影响滑块热力学性能的因素主要可以归结为加热器高度、热生成率以及材料的传热系数;空气轴承力及工作表面热变形的双重作用决定了滑块飞行高度的改变.仿真结果为磁头滑块加热器的设计及空气轴承动力学特性分析提供了依据.     

Ultra low head–disk spacing measurement using dual beam polarisation interferometry

In this paper, a dual-beam normal incidence polarisation interferometer is proposed to measure the flying height or head–disk spacing. Using this interferometer, the head–disk spacing can be measured both in magnetic real disk condition and in glass disk condition. It has the advantage of both the currently popular intensity interferometry method and the oblique incidence polarisation interferometry method. With this polarisation interferometer, not only the flying height can be measured down to contact without losing accuracy, but the pitch and roll of the head-slider can also be detected dynamically. The optical parameters of the head-slider can also be determined. Design details and experimental study are presented.     

Towards fly- and lubricant-contact recording

Reducing the spacing between the magnetic head and the magnetic media is of crucial importance in enabling future high-density magnetic data storage. The magnetic spacing has been reduced to a level that we have to explore new schemes for the further reduction of the spacing. This paper reports authors’ efforts towards fly- and lubricant-contact recording scheme. The targeted objective is to minimize the mean-plane spacing between the slider and disk surfaces and to allow the further reduction of the overcoat thickness. The slider will still fly over the disk surface. The read/write head part of the slider will be protruded to contact lubricant—to minimize the mean-plane mechanical spacing. The key factors for achieving such a mechanism include super-smooth slider and disk surfaces, advanced slider air-bearing design to significantly reduce flying height modulation caused by disk waviness and flatness, nano-actuator design, position feedback control scheme to control the contact depth, and so on. The preliminary experimental data confirm the feasibility of such a lubricant-contact scheme. The slider air-bearing design presented in this work also indicates the feasibility of high-performance slider design, which can well follow the disk waviness. A parameter, anti-modulation factor, is introduced for the evaluation of slider's performance in reducing flying height modulation caused by disk waviness.     

Engineering issue study of triple harmonic method for in situ flying height analysis

In situ flying height testing technology is becoming more and more important in slider–disk interaction analysis and manufacturing quality control of disk drives and head-related components. Triple harmonic method is a quite promising choice for in situ flying height analysis, compared with other in situ methods reported up to now. This paper reports results of investigations on engineering issues of applying triple harmonic method for in situ flying height analysis. The paper reports results of analysis on the effects of various testing conditions on flying height testing repeatability and accuracy. Results suggest that working at reasonable high channel density and working on the ratio between third and first harmonics will be an advantage in terms of both flying height testing sensitivity and testing repeatability. Comparing with media thickness effect, the gap-length variation among different heads will be important if it is to study flying height difference among different heads and the testing is at high channel density. Also, it is suggested to work at AC erased track, in order to reduce the non-linearity caused by hard transition.     

Head–disk interface problems in first-surface near-field optical recording with flying optical head

Near-field recording (NFR) technology using a flying optical head is applied for high density optical data storage. Diamond-like carbon (DLC) film and PFPE lubricant film are coated on utmost NFR disk to reduce the tribological problems. A contamination at the head–disk interface (HDI), especially on a solid immersion lens (SIL) is observed. The contaminants are composed of dust materials from the surroundings and lubricant materials from a disk surface. The contaminants are supposed to be condensed by heat from a writing laser beam at the HDI. To avoid the contamination problem, a cover-layer is coated and a focal plane moved under the cover-layer from the HDI. First-surface near-field recording configuration can be modified by laminating a cover-layer, which enhances the possibility of a practical application with a media removability function.     

Interface solution for writing-induced nano-deformation of slider body

Writing-induced nano-deformation of slider body becomes a big concern when the mechanical spacing between the head and disk is continuously reduced to achieve higher magnetic recording areal density. Reduced head–disk spacing increases the risk of head/disk contact and causes the thermal instability in head–disk interface (HDI). This paper reports authors’ efforts towards exploration of interface solutions for writing-induced instability in ultra-low head–disk spacing magnetic system. Multi-shallow step structure with optimized rail position is analyzed and a new femto slider with such structure is explored. The results of numerical simulation indicate that the multi-shallow step structure is an effective approach in reducing the flying height change caused by the writing-induced nano-deformation of the slider body.     

Disk clamping distortion and slider crown sensitivity induced flying height variation

The disk clamping distortion and slider crown sensitivity induced flying height (FH) variation is investigated. The experimental results which were measured with in situ method were compared with simulated numerical results. Both results indicate that the disk clamping distortion has significant influence on the FH variation. Crown sensitivity of the sliders is one of the factors that determine the amplitude of the FH variation. Higher crown sensitivity sliders exhibit greater FH variation.     

旋转飞行器动稳定导数获取原理

旋转飞行器具有独特的周期性非定常气动现象，其动态特性更加复杂，气流与旋转高度非定常关联，俯仰阻尼导数和Magnus力矩导数同等重要.文章从飞行器气动力建模的理论基础出发，考虑飞行器自转角速度非零的事实，将其作为基态影响参数，重新构建了旋转飞行器气动力数学表达式，并借鉴成熟的常规动导数强迫振动法，采用Fourier级数表征旋转影响，沿用旋转飞行器周期气动等效概念，建立了基于基态旋转流场的周期气动等效平均俯仰动稳定导数、纵向洗流时差导数和滚转动稳定导数获取的原理表达式，并设计了相应的运动模式，可供数值计算和风洞实验使用.      

不同运动状态下的飞机目标雷达散射截面积统计特性分析

目标的运动状态对其动态雷达散射截面积(RCS)起伏特性具有十分重要的影响,同一目标在不同运动状态下,可能具有不同的RCS起伏模型。结合实测数据,对在平稳直线飞行和曲线机动飞行两种状态下的飞机动态RCS进行统计分析。分析结果表明：在平稳直线飞行状态下,飞机目标的动态RCS起伏模型与观测视角内的静态RCS起伏模型近似;在曲线机动飞行状态下,飞机目标的动态RCS起伏更显著、更随机,当观测时间足够长、目标的运动随机性更大时,其起伏模型更接近于指数分布。     

Numerical simulation of the EM scattering and Doppler spectrum of a low flying target above dynamic oceanic surface by using the FEM-DDM method

The Doppler (DP) spectrum of a moving target such as a ship, an iceberg or an air-plane above dynamic oceanic surfaces[1—3] is one of the most important subjects for ra-dar oceanic surveillance, target tracking and oceanic remote sensing[4—7]. With the ad-vancement of oceanic remote sensing and radar surveillance, the experimental observa-tion and theoretical modeling of oceanic clutter have been extensively studied, e.g. by using oceanic field measurement, wave tank experiment and some stud…     

A Wavelength and Spectrum Measurement of an Extremely-Short-External-Cavity Laser Diode by Precisely Controlling Slider Flying Height

In this paper we propose a measurement method that uses a laser diode (LD) attached to a flying slider and a semi-transparent rotating disk mirror for an extremely-short-external-cavity configuration. Not only the wavelength, but also the spectrum and the light output are measured at room temperature with the external cavity length, the reflectivities of the LD facets and the external mirror, and the drive current as parameters. We have confirmed wavelength variation as great as 30 nm by changing the external-cavity length for a 1.3-$mUm wavelength laser diode with an antireflection coating on the LD facet facing the external mirror.     

Lubricant film flow and depletion characteristics at head/disk storage interface

The characteristics of lubricant film at head/disk interface(HDI) are essential to the stability of hard disk drives. In this study, the theoretical models of the lubricant flow and depletion are deduced based on Navier–Stokes(NS) and continuity equations. The air bearing pressure on the surface of the lubrication film is solved by the modified Reynolds equation based on Fukui and Kaneko(FK) model. Then the lubricant film deformations for a plane slider and double-track slider are obtained. The equation of lubricant film thickness is deduced with the consideration of van der Waals force, the air bearing pressure, the surface tension, and the external stresses. The lubricant depletion under heat source is simulated and the effects of different working conditions including initial thickness, flying height and the speed of the disk on lubricant depletion are discussed. The main factors that cause the lubricant flow and depletion are analyzed and the ways to reduce the film thickness deformation are proposed. The simulation results indicate that the shearing stress is the most important factor that causes the thickness deformation and other terms listed in the equation have little influence. The thickness deformation is dependent on the working parameter, and the thermal condition evaporation is the most important factor.     

The stability of rolling motion of hypersonic vehicles with slender configuration under pitching maneuvering

The configurations of near space hypersonic flying vehicles are considerably different from those of conventional aircrafts.Their configurations are relatively slender;hence their moment of inertia around the longitudinal axis is much smaller than those around the other two axes,resulting in strong coupling of rotations around the three axes.Thus,the stability analysis of rolling motion for such flying vehicles is more complicated than those for conventional aircrafts,and there is no available result of stability analysis which can readily be applied to such cases.This paper is mainly concerned with the stated problem.Considering the practical situation,our investigation is targeted a slightly simpler problem,namely the rolling stability of flying vehicle under known pitching motion.The stability criterion of rolling motion is obtained with and without lateral motions.We also conducted numerical simulation for the pitching-rolling coupled motions of flying vehicles by solving Navier-Stokes equations coupled with dynamic equations of flight.The results of simulation agree well with those of theoretical analysis and experiments.     

Dynamic stiffness of biological tissues in a model with assigned displacements at the surface of a half-space

The results of developing a model that describes the formation of the dynamic stiffness of biological tissues are presented for the case where the dynamic stiffness is measured by pressing a circular flat vibrating disk into the tissue normally to its surface while both the disk and the stationary frame of the measuring device are in contact with the tissue surface. Analytical expressions in quadrature form are derived for the dynamic stiffness of tissues by using the model of a half-space with preset displacements of its surface. Numerical calculations are performed, and the agreement with the experiments is demonstrated for the effects caused by the tight contact of the tissue surface with the stationary frame of the measuring device.     

ANALYSIS OF NON-LINEAR DYNAMIC STABILITY FOR A ROTATING SHAFT-DISK WITH A TRANSVERSE CRACK

In this paper, the nonlinear dynamic stability of a rotating shaft-disk with a transverse crack is studied. The crack and the disk are located in arbitrary positions of the shaft respectively. Using the equivalent line-spring model, the deflections of the system with a crack are constructed by adding a deflection to the deflections of the uncracked system. The unstable regions are confirmed by Runge-Kutta method and the Floquet theory. The effects of crack depth, crack position, disk position, disk thickness and rotating speed on the principal unstable regions are discussed. The numerical results are compared with available data.     

影响激光加热运动圆柱体的加热线型的分析

 采用几何分析的方法研究激光加热运动圆柱体的过程，在说明加热线型的概念和意义后，讨论了在地平面上各点处所具有的加热线型的时间宽度，从而指出，为了激光有效加热运动圆柱体，激光器应当怎样在地平面上放置的原则。即根据激光器有效工作时间与圆柱体抛射时间的比例关系选择一定的相对时间宽度等值线，以此等值线为界在地平面上划出一有效区域，并从中选取距离轨道最近的点作为激光器的放置点。当考虑大气对激光的衰减作用时，激光以小于一定入射角阈值进行动态加热的总能量将出现极大值，在此处放置激光器最有利于动态加热。     

Vibrational response of a moving suspension-slider loading system exciting a rotating flexible disk

To investigate the vibrational response of the magnetic read/write head in hard disk drives this paper models a rotating flexible disk excited by a moving suspension-slider system which is considered to be a mass-dashpot-spring loading system, with the initial unstressed transverse runout integrated into the rotating disk dynamic model. The slider motion on the disk surface is driven by the suspension rotating at a constant speed. By subtracting the steady-state deflection component from the instantaneous deflection response of the rotating disk system, the relative vibration transverse deflection of the slider caused by the motion of the suspension-slider loading system is obtained. The effects of the slider initial and final positions, speed of movement, the disk rotational speed, and the disk mode of the initial transverse runout on the maximum amplitude of the relative vibration deflection are analyzed.     

磁光盘可靠性及寿命评估方法研究

采用高温和湿热交变加速应力条件对磁光盘可靠性寿命进行研究。通过对磁光盘在加速应力条件下的动态性能分析，提出了以威布尔分布来处理磁光盘失效的理论模型，并得到了较好的拟合，对磁光盘的可靠性寿命进行了评估，得到了磁光盘的可靠性寿命以及威布尔寿命分布函数。