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5/22/98

NEW TECHNIQUE CREATES DURABLE AUDIO AND VIDEO TAPES, DATA DISKS

COLUMBUS, Ohio -- Researchers at Ohio State University have found a way to extend the life of magnetic audio and video tapes and data storage disks.

This work may help to solve a problem facing manufacturers of the newest digital media: how to create surfaces on magnetic tapes and disks that are hard enough to resist wear, but flexible enough to survive contact with the devices that use them.

“Many factors affect the performance of magnetic tapes and disks,” said Bharat Bhushan, Ohio Eminent Scholar and the Howard D. Winbigler professor of mechanical engineering. “Because manufacturers don’t know exactly which parameters are most important, they can’t consistently create optimum surfaces. Now we know it can be done.”

The texture of the surface is important -- a smooth surface stores more data; if it’s too smooth, however, the tape or disk will stick to the machinery it’s played on. That’s because the large contact area between the tape or disk and the reader will create a great deal of static friction.

Bhushan and Steven Patton, a physics doctoral student, experimented with different coatings for magnetic tapes and discovered how manufacturers may balance all these factors. Some of the work appeared in a recent issue of the journal IEEE Transactions on Magnetics. The work on optimization of surface roughness appeared in documentation for a U.S. patent issued in early April.

Magnetic tape and disk coatings normally consist of fine sprays of magnetic powder with a thin lubricant film on top. Two of the parameters involved in the coating are skewness, or symmetry, and kurtosis, which has to do with the distribution of the particles in the magnetic powder.

Bhushan and a mechanical engineering doctoral student, Sameera Chilamakuri, have shown that a particular range of skewness and kurtosis would provide a surface free from static friction. They’ve also found a way to optimize the thickness of the lubricant film -- another important factor.

The research paper focuses on Bhushan and Patton’s investigation into video tapes with a diamondlike carbon (DLC) coating, so named because the coating is made of carbon powder that approaches the hardness of diamond.

Commercial companies often use DLC tapes for audio, video, and data recording. Most people wouldn’t use DLC tapes at home unless they owned a digital VCR or camcorder. Bhushan said that DLC tapes, which provide for ultra-high recording density, should become more common over the next three to five years.

At issue is how to make a DLC coating for tapes that store a great deal of data that won’t wear out so quickly. For video tapes, wear makes itself visible in static or skips in the picture. For data storage disks, wear appears in the form of lost data.

For this study, the researchers ran three types of video tapes through a commercial VCR. One was a typical flat tape with a DLC coating, and the other two were tapes without a DLC coating, one flat and the other wavy. They played and rewound the tapes until they wore out completely, and examined how the tapes performed when the VCR was in pause mode.

The wavy tape lasted the longest, through 850 play and rewind cycles. The flat DLC-coated tape finished second, with 500 cycles, and the flat non-DLC tape finished last with 350 cycles. The DLC-coated tape performed the best in pause mode, however.

The researchers concluded that while the DLC coating improved the durability of flat tape, it’s not as reliable as it could be, for three reasons:

“We think manufacturers are making the surface of the tapes too rough,” said Bhushan. “The carbon may also be too hard. They may have to give up some of the hardness they have now to have the flexibility they’re looking for.”

“The third recommendation we are making,” continued Bhushan, “is that manufacturers must control one parameter in particular -- the ratio of lubricant film thickness to the surface roughness of the tape.”

The technology that the researchers have patented is a method to calculate the right balance of hardness and roughness, and relate those measures to the right thickness of lubricant film. Bhushan said the principle applies to both video tapes and data storage disks.

Bhushan will continue to work with manufacturers to get samples of new DLC-coated tapes and tapes with optimized topography, to see if they can improve the performance further.

This work was sponsored in part by a consortium of magnetic media manufacturers. Other sponsors included the Advanced Technology Program at the Department of Commerce and the Defense Advanced Research Projects Agency -- the central research and development organization for the Department of Defense.

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Contact: Bharat Bhushan, (614) 292-0651; Bhushan.2@osu.edu
Written by Pam Frost, (614) 292-9475; Frost.18@osu.edu