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.
