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

本文研究了一种利用表面声波进行润滑的新型机械界面。在这个概念中，SAW？S用于实现以高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。如果在两个相对运动的表面之一上激发一个移动的SAW，并且接触点（即移动SAW的峰值）具有与两个表面之间的相对速度相同的水平速度，那么接触点将不会经历任何摩擦。零滑动速度接触点的创造使有效摩擦最小化，而无需使用任何润滑剂，因此可以实现许多新应用。这是与超声波电机相反的效果，超声波电机使用SAW？S在两个表面之间产生摩擦力。这个概念在本质上是一个主动机械轴承。本研究的主要目的是获得关于声表面波动力学的新认识。S及其对界面摩擦学性能的影响。这些新的认识有望导致革命性的新技术，以抑制运动表面之间的摩擦和磨损。在本研究中，使用定制的实验装置研究声表面波在各种复杂几何形状上的动力学，如声换能器、波导、耦合器等。此外，还研究了声场与材料的各种相互作用。这些研究将带来SAW动力学、各种应用的功能声学元件设计以及弹性材料的动态/摩擦学特性方面的基本新知识。虽然作为一种新形式的轴承的一般应用显然很重要，但这种新技术可以实现几种特定的应用。最显著的例子之一是硬盘驱动器（HDD）。在HDD中，读取和写入数据的磁头在由空气轴承支撑的旋转磁盘上方飞行。为了防止机头和圆盘之间的摩擦和磨损，需要有限的分离。同时，为了获得良好的写入效率和读取灵敏度，距离必须尽可能小，因为随着距离的增加，磁场呈指数衰减。为了满足未来的数据存储需求，有必要将这种距离减少到5nm，这是一个巨大的挑战，因为在这些距离上控制头部高度和防止接触是困难的。此外，空气轴承技术产生的气流在hdd中消耗大量功率，而hdd是IT基础设施总功耗的重要组成部分。他们的用电量占美国总用电量的1.5%（2006年，EPA）。所提出的概念提供了一种新的、革命性的方法，将磁头与磁盘耦合在一起，零摩擦，以实现更高的记录密度，并且还可能使HDD在降低内部气压的情况下运行，这将大大降低HDD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.