Near Frictionless Surface Acoustic Wave Active Bearing for Disk Drive and Other Applications

本文研究了一种利用声表面波(SAW)进行润滑的新型机械界面。在这一概念中，声表面波S被用来实现高速相对速度滑动的两个表面之间零有效摩擦的直接接触界面。如果在相对于彼此运动的两个表面中的一个表面上激励移动锯，并且作为移动锯的尖峰的接触点具有与两个表面之间的相对速度相同的水平速度，则接触点不会受到任何摩擦。零滑动速度接触点的创建将有效摩擦力降至最低，而无需施加任何润滑剂，从而实现了一系列新的应用。这是超声波电机的相反效果，超声波电机使用SAW？S在两个表面之间产生摩擦力。这一概念实质上是一种主动机械轴承。本研究的主要目的是对声表面波S的动力学及其对界面摩擦学性能的影响有新的认识。这些新的理解有望带来革命性的新技术，以抑制运动表面之间的摩擦和磨损。在这项研究中，使用定制的实验装置来研究声表面波在各种复杂几何结构上的动力学，如声换能器、波导、耦合器等，并研究了声场与材料的各种相互作用。这些研究应该会带来关于声表面波动力学、各种应用的功能声学部件设计以及弹性材料的动力学/摩擦学特性的基本新知识。尽管作为一种新形式的轴承的一般应用显然很重要，但这种新技术可能会使一些特定的应用成为可能。最引人注目的例子之一是硬盘驱动器(HDD)。在HDD中，读写数据的磁头在由空气轴承支撑的旋转磁盘上方飞行。需要有限的间隔以防止磁头和磁盘之间的摩擦和磨损。同时，为了获得良好的写入效率和读取灵敏度，间隔必须尽可能小，因为磁场随着间隔的增加呈指数衰减。为了满足未来的数据存储需求，有必要将这种间隔减小到5 nm，这是一个巨大的挑战，因为在这些距离上很难控制磁头高度和防止接触。此外，气浮技术产生的气流会消耗硬盘中的大量电力，而硬盘在IT基础设施中占总电力消耗的很大一部分。他们的电力消耗占美国总用电量的1.5%(2006年，美国环保局)。提出的概念提供了一种新的革命性方法，以零摩擦将磁头耦合到磁盘以实现更高的记录密度，并且硬盘还可以在降低内部气压的情况下运行，这应该会显著降低硬盘的功耗。

This research investigates a novel mechanical interface which utilizes surface acoustic waves (SAW) for lubrication. In this concept, SAW?s are used to realize a direct contact interface with zero effective friction between two surfaces sliding at high relative velocities. If a traveling SAW is excited on one of the two surfaces moving relative to one another, and the contact points, which are the peaks of the traveling SAW, have the same horizontal velocity as the relative velocity between the two surfaces, the contact points will not experience any friction. The creation of zero-sliding-velocity contact points minimizes effective friction without applying any lubricants and, as a result, enables a host of new applications. This is the converse effect to ultrasonic motors, which use SAW?s to create friction forces between two surfaces. This concept in essence is an active mechanical bearing.The main objective of this research is to gain new understanding about the dynamics of SAW?s and their effects on the tribological properties at interfaces. These new understandings are expected to lead to revolutionary new techniques for suppressing friction and wear between moving surfaces. In this research, custom experimental apparatuses are used to study the dynamics of SAW on various complex geometries, such as acoustic transducers, wave guides, couplers, etc. Also, various interactions of the acoustic field with materials are studied. These studies should lead to fundamental new knowledge about SAW dynamics, functional acoustic component design for various applications and dynamical/tribological properties of elastic materials.While general applications as a new form of bearing are obviously important, there are several specific applications that may be enabled by such a new technology. One of the most striking examples is in the hard disc drive (HDD). In a HDD, a magnetic head, which reads and writes data, flies above a rotating magnetic disc supported by an air bearing. A finite separation is needed to prevent friction and wear between the head and the disc. At the same time, the separation has to be as small as possible for good write efficiency and read sensitivity, because the magnetic fields decay exponentially with increasing separation. To meet future data storage needs it is necessary to reduce this separation to 5nm, an immense challenge since controlling the head height and preventing contact is difficult at these distances. Moreover, the creation of air flow for the air bearing technique consumes significant power in HDDs, and HDDs are a significant portion of the total power consumption in the IT infrastructure. Their power consumption accounts for 1.5% of the total electricity usage in US (2006, EPA). The proposed concept provides a new, revolutionary means to couple the head to the disc with zero friction to achieve higher recording density, and also has the possibility for a HDD to operate with reduced internal air pressure, which should significantly reduce HDD power consumption.