Surface Acoustic Wave – Active Bearing (SAW-AB)

In this research we propose the investigation of a novel mechanical interface which we call the surface acoustic wave active bearing (SAW-AB).  Tribology has long been a serious concern at the sliding mechanical interface and numerous efforts have been made to understand and control the tribology in the interface design. Our a new approach uses surface acoustic waves (SAW) to create a direct contact interface with zero effective friction between two surfaces moving at high relative velocities. This is the opposite of ultrasonic motors (USM), which use SAW and friction to create forces between two surfaces. In the SAW-AB both surfaces move relative to one another and the contact point does not move, however. The creation of zero-velocity contact points eliminates the need for lubricants and concerns about friction and also enables a host of new applications. The SAW-AB in essence is an active mechanical bearing.

Experimental Demonstration


Integrated with this research programs is an ongoing effort for the development of new interdisciplinary courses within our department that focus on the fundamentals of mechanics, tribology and metrology. Our research effort is formed from an interdisciplinary group of PIs from Mechanical Engineering and Electrical and Computer engineering.

Intellectual merit: The main objective of this research is to gain new understanding about the dynamics of SAW and the interface of traveling SAW and moving surfaces that we believe will lead to a revolutionary new technique for suppressing friction and wear between moving surfaces. In this research we will develop a custom experimental apparatus to quantitatively characterize the dynamics of SAW on various structures. We will examine the dynamics of SAW in complex geometries, such as acoustic transducers, wave guides, couplers as well as general SAW dynamics such as interferences and diffraction. We will also study various interaction of the acoustic field with materials. A few examples of our particular interest are the effect of inhomogeneity, anisotropy or non-linearity of the elastic properties on the SAW propagation, effects of intense acoustic field on the material, in other words, acoustic power capability. These studies should lead to fundamental new quantitative knowledge about SAW dynamics and functional acoustic component design for various applications.

Broader impacts: 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, and impactful, examples is in the hard disc drive (HDD). In a HDD a magnetic head, which reads and writes information, flies above a rotating magnetic disc supported by an air bearing. Typical distances between the head and disc, including protection overcoat and lubricant layers, are on the order of 10 nm.  A finite separation is needed to prevent friction between the head and the disc. The separation distance directly affects the writing efficiency of the head since the magnetic fields reduce quadratically in distance. To meet future data storage needs of 1Tb/inch2 and beyond, it will be necessary to reduce this separation to <5nm, an immense challenge since controlling the head height and preventing contact is incredibly difficulty at these distances.  Moreover, the energy necessary to create air flow for the air bearing technique is a significant part of the HDD power consumption. Coupled with the fact the EPA estimates that about 1.5% of the total electricity generated in the US is consumed for running data centers as of 2006, and it is steadily increasing about 15% annually, equivalent to doubling every 5 years, the air bearing represents an tremendous energy waste. The proposed SAW-AB provides a new, revolutionary means to directly couple the writing head to the media with zero friction to achieve higher recording density, and has the possibility for a HDD to operate with reduced internal air pressure, which should significantly reduce HDD power consumption.