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.     

基于椭圆偏振显微镜的纳米级磁头润滑膜观测方法

针对磁头飞行导致液体润滑膜的转移研究以及润滑膜在磁头上的动态变化特性观测问题,基于改进的垂直物镜的椭圆偏振显微镜,提出起偏器相移方法的磁头表面润滑膜厚度计算模型,实现了润滑膜厚度的测量。实验以非极性润滑剂Z03覆盖的磁头为样品对椭圆偏振显微镜进行标定,以极性润滑剂Zdol4000作为样品,对其在磁头表面的去湿现象进行观察。该方法测量精度可达0.37 nm,分辨力约0.36 μm,可为其他纳米级薄膜观测提供一定的技术参考。     

Investigation of HDD Ramp Unloading Processes with an Efficient Scheme

Ramp load/unload (L/UL) mechanisms are widely used to rest sliders in hard disk drives (HDDs). Loading/unloading a slider swiftly and smoothly is crucial in a HDD design. A novel, efficient simulation scheme is proposed to investigate the behaviors of a head disk interface (HDI) in ramp unloading processes. A dual scale model is enabled by decoupling the nano-meter scale change of an air bearing and the micro- or milli-meter scale deformation of a suspension. A modified Reynolds equation governing the air bearing was solved numerically. The slider design was characterized with performance functions. Three stages in an unloading process were analyzed with a lumped parameter suspension model. Key parameters for the model were estimated with a comprehensive finite element suspension model. Finally, simulation results are presented for a commercial HDI design.     

Using angle resolved ESCA to characterize Winchester disks

Recent improvements in ESCA instrumentation have led to a renewed interest in the use of angle resolved ESCA to study thin (<75 Å) film structures such as the fluocarbon lubricants on Winchester disks. Monitoring disk production with ESCA to assure optimal lubricant thickness is an essential part of disk manufacture. Assumptions are made about the morphology of the disk surface and the vacuum integrity of the lubricant. Angle resolved ESCA reveals the shortcomings of these assumptions and establishes the conditions required for valid lubricant thickness measurements. Angle resolved ESCA also identifies any surface contamination covering the lubricant and suggests the molecular orientation of the lubricant.     

On the tribological characteristics of dynamically loaded journal bearing with micropolar fluids

The addition of the additives to the lubricant oil to enhance the characteristics of the lubricant will influence the performance of the bearings. Based on the theory of micropolar fluids, the tribological characteristics of a dynamically-loaded journal bearing are numerically studied. Comparisons are made between the Newtonian fluids and the micropolar fluids. It is shown that for a dynamically-loaded journal bearing, the micropolar fluids yield an increase not only in the friction force, but also in the friction coefficient. In addition, the oil film pressure and the oil film thickness are obviously higher than that of Newtonian fluids.     

On the tribological characteristics of dynamically loaded journal bearing with micropolar fluids

The addition of the additives to the lubricant oil to enhance the characteristics of the lubricant will influence the performance of the bearings. Based on the theory of micropolar fluids, the tribological characteristics of a dynamically-loaded journal bearing are numerically studied. Comparisons are made between the Newtonian fluids and the micropolar fluids. It is shown that for a dynamically-loaded journal bearing, the micropolar fluids yield an increase not only in the friction force, but also in the friction coefficient. In addition, the oil film pressure and the oil film thickness are obviously higher than that of Newtonian fluids.     

液滴碰撞液膜润湿壁面空气夹带数值分析

采用复合水平集-流体体积法并综合考虑传热及接触热阻的作用, 对液滴碰撞液膜润湿壁面空气夹带现象进行了数值分析. 揭示了夹带空气形成机理, 探索了夹带空气特性参数随碰撞速度和液膜厚度的变化规律, 获得了夹带空气作用下液滴碰撞润湿壁面的传热机理. 研究结果表明: 撞壁前气液两相压力差是引起气液相界面拓扑结构变化以及夹带空气形成的主要原因; 液滴碰撞速度与压缩空气层内压力以及相界面形变高度密切相关; 液滴接触液膜时, 碰撞轴上液滴底部和液膜表面速度相等, 大约是碰撞速度的1/2; 碰撞速度对夹带空气层底部到破碎点的无量纲弧长和最大无量纲夹带空气直径均存在较大的影响; 液滴和液膜的无量纲形变高度与斯托克斯数密切相关; 液膜初始厚度对液滴和液膜的无量纲形变高度和最大无量纲夹带空气直径影响较大; 撞壁初始阶段, 碰撞中心区域夹带空气对壁面热流密度分布存在较大的影响.     

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.     

Improvement of least-squares finite difference method on simulating slider air bearings in head disk systems

Least-squares finite difference (LSFD) method, one of mesh-free methods, is used to solve slider air bearings problem through discritizing the generalized Reynolds equation into nonlinear systems of algebraic equations. Two approximation schemes for the linearization of these equations are presented and compared. And, some new techniques to search supporting points for the reference node in the mesh-free method were proposed and explored. Therefore, these improvements eliminate some potential limitation of the LSFD method previously published and further facilitate its employment in complex slider models. Advanced step slider as an example of negative pressure sliders is simulated and verified using the improved LSFD mesh-free method in head disk systems.     

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.     

分离压和表面黏度的协同作用对液膜排液过程的影响

针对含不溶性活性剂的垂直液膜排液过程,在考虑分离压作用的前提下,引入随活性剂浓度变化的表面黏度模型,应用润滑理论建立了液膜厚度、活性剂浓度和液膜表面速度的演化方程组,通过数值计算分析了常表面黏度和变表面黏度情形下的液膜演化特征.结果表明:表面黏度是影响液膜排液过程的重要因素,当不考虑表面黏度时,液膜表面呈"流动"模式,反之呈"刚性"模式,且随表面黏度增加,液膜排液速率明显减缓.分离压对"黑膜"的形成至关重要,分离压单独作用时,其形成的"黑膜"长度较短,而只考虑表面黏度时,则不能形成稳定的"黑膜".而在二者协同作用下,液膜中部形成了向下扩展、厚度很薄但非常稳定的"黑膜",且"黑膜"厚度、出现时间均随表面黏度的增大而增加.当考虑活性剂浓度对表面黏度的影响时,表面速度受此影响显著;在形成"黑膜"长度及出现时间方面与相应常表面黏度的情形基本类似,但其"黑膜"厚度小于相应常表面黏度,故在液膜排液过程中更容易发生失稳.     

金属-电介质约束的半导体微盘激光器

设计了一种以半导体材料InGaAsP作为核心结构的器件表面蒸镀二氧化硅膜层,在其上蒸镀金膜层,构成金属-电介质半导体微盘激光器结构,盘面的厚度为2 μm,盘面半径为6 μm,盘壁侧表面与底面的夹角为45°.使用有限元法对该结构器件的回音壁模式进行数值研究,利用所谓"偏微分方程的弱项形式"有效地抑制了许多局域不变性相关的"伪解".通过数值求解弱项型矢量亥姆霍兹方程,得到微盘激光器回音壁模式的横磁场分布,在此基础上讨论了其品质因数(Q值)、模体积、不同金属和电介质膜厚度对器件品质因数的影响、盘的半径和其品质因素的关系等相关量.理论计算表明,这种结构的器件较直接在介质表面蒸镀金属膜层结构的器件的品质因数高2～3倍.实验还获得了基阶和高阶的表面等离子体波模式,以及品质因数最大达到约5 400的光学-电介质基模.     

Starved elastohydrodynamic lubrication theory: application to emulsions and greases

In classical fluid lubrication the film thickness is mainly determined by entrainment velocity and oil viscosity. At high pressure, elastic deformation occurs changing the local geometry: this is the elastohydrodynamic lubrication regime (EHL). When a limited amount of lubricant is available to the contact, a component failure due to lubricant starvation can result. A new starvation model is presented, using the amount of oil on the surfaces as the key parameter controlling starvation. It is successfully applied to describe the contacts lubricated with multi-phase fluids such as emulsions and greases, which combine starvation with a very complex rheology.     

Dynamics of heat and mass transfer through a water-air interface based on measurements of thermal radio emission at a frequency of 60 GHz

We study the dynamics of heat and mass transfer through a water-air interface on the basis of laboratory radiometric measurements of the time dependence of thermal radio emission of water at a frequency of 60 GHz, which is related to air turbulization above its surface by a fan. We recover the dynamics for the temperature profile in water and in a viscous sublayer of air as well as for the heat flux through the water-air interface. The flux components related to evaporation and heat exchange and the rate of evaporation from a unit surface are determined. An equation for determining the thickness of the viscous sublayer in the air from the heat flux value is obtained;this thickness is about 2 mm under the experimental conditions. The process dependence on the water turbulence is established and methods for determining the thermal film thickness are proposed. In the absence of turbulence in unstable stratified water we observed the development of a periodic convective process from the time the critical value of the Rayleigh number was reached. The heat exchange dependence on the presence of petroleum film on the water surface is studied. It is found that for a film thickness of 5 μm the heat exchange rate decreases by a factor of 3 because of the petroleum presence. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 3, pp. 351–369, March, 1997.     

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.     

Performance of Non-Contact Linear Actuators Driven by Surface Acoustic Waves*

A new kind of non-contact linear actuator （motor） driven by surface acoustic waves （SAWs） is presented, in which the stators are made from SAW delay lines using 128° YX-LiNbO3 substrates. A fluid layer is introduced between the slider and the stator of the actuator, and the slider is a circular aluminum disk suspended on the surface of the liquid （water） layer. As the SAW is excited on the stator, the SAW is converted to a leaky wave in the interface of the stator and the liquid, and then propagates into the liquid. Owing to the nonlinear effect of wave propagation, acoustic streaming is generated, which pushes the slider to move. By the experiments, the relations between the slider velocity and the experimental parameters, such as the exciting voltage of the SAWs, the thickness and the kinematic viscosity of the liquid layer, are obtained.     

Elastic friction drive of surface acoustic wave motor

Importance of elastic deformation control to obtain large output force with a surface acoustic wave (SAW) motor is discussed in this paper. By adding pre-load to slider, stator and slider surfaces are deformed in a few tens nanometer. Appropriate deformation in normal direction against normal vibration displacement amplitude of SAW existed. By moderate deformation, the output force of the SAW motor was enlarged up to about 10 N and no-load speed was 0.7 m/s. To produce this performance, the transducer weight and slider size were only 4.2 g and 4 x 4 mm(2).By traveling wave propagation, surface particles of the SAW device move in elliptical motion. Due to the amplitude of the elliptical motion is 10 or 20 nm order, the contact condition of the slider is very critical. To control the contact condition, namely, the elastic deformation of the slider and stator surface in nanometer order, a lot of projections were fabricated on the slider surface. The projection diameter was 20 micro m. In static condition, the elastic deformation and stress were evaluated with the FEM analysis. From this calculation and the simulation result, it is consider that the wave crest is distorted, hence the elasticity has influence on the friction drive condition.Elastic deformation of the stator surface beneath the projection from the initial position were evaluated. In 4 x 4 mm(2) square area, the sliders had from 1089 to 23,409 projections. Depression was independent to the contact pressure. However, the output force depended on the depression although the projection density were different. From the view point of the output power of the motor, the proper depression was independent to the projection density. Around 25 nm depression, the output force and output power were maximized. This depression value was almost same as the vibration displacement amplitude of the stator transducer.     

微液膜动力学特性与稳定性实验研究

气-液两相流设备的性能受限于临界热流密度,开展流动微液膜动力学特性及其稳定性的相关研究是深入理解沸腾危机及临界热流密度机理的关键。采用光学玻璃制成的矩形通道作为实验段,使用微流量齿轮泵驱动去离子水,使其在实验通道入口处与在其上部流动的压缩空气接触形成同向流动的分层流。利用共轭光学探测器对流动微液膜的厚度进行了测量,利用高速摄像机对气-液两相分层流波动特性进行了可视化观测。研究表明,在绝热情况下,当液速一定时,液膜的平均厚度随着气速增加而减小,当气速增加到某一阈值时会导致液膜破裂。     

Film-thickness Error Analysis of Optical Disk Systems

It is difficult to exactly control the film thickness of optical disk multilayer in the actual coating process. The thickness error becomes a main factor affecting the optical characters of the film system. The thickness error′s sensitivity factor of dielectric optical multilayer is derived from the optical matrix in this paper. The effect of the thickness error on the reflectivity or reflectivity contrast of the optical disk multilayer is analyzed with a numerical calculation. The sensitivities to thickness error for different layers or in different film-thickness ranges are compared and discussed. A sketchy method defining allowable thickness error is given. Some experimental results verify the applicability of our theoretical analysis.     

Film-thickness Error Analysis of Optical Disk Systems

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