During their first year of work, the researchers learned that data could remain on diskettes that had been subjected to high heat, and had to abandon thermal destruction techniques because of the fire and harmful gases they generated. That left only magnetic techniques.
In developing techniques for complete erasure, the researchers first had to learn how different data storage drives operate, then assess the magnetic field levels necessary for complete erasure. To do that, they obtained a number of commercially-available micro-drives, cut the media into sections, subjected them to varying magnetic fields, and then tested the sections with the MFM.
"We had to understand how the data is laid out on the disk so we could know where to look for the patterns, and we had to do a lot of measurements to determine exactly what kind of magnetic field is needed to destroy all data," said Knotts. "We had to do a lot of destructive testing to determine that, and our lab is littered with the carcasses of dead hard drives to prove it."
Producing a magnetic field sufficient to destroy data patterns required the use of neodymium iron-boron magnets custom-designed for the project and special pole pieces made of esoteric cobalt alloys. The magnets, which weigh as much as 125 pounds, had to produce fields sufficient to penetrate metallic housings that surround some drives.
"We developed models for magnetic circuits that we could run through optimization codes to design the best shape to get the field that we needed," Knotts said. "It takes quite a magnetic field to get through the steel enclosures on some of the drives. We are producing magnetic fields comparable to those used in magnetic resonance imaging equipment, so these are not your ordinary refrigerator magnets."
Mechanically, the researchers faced challenges in reliably moving data storage devices through the magnetic fields. In some cases, aircraft crews would simply insert removable media into a motorized mechanism that pushes them past the magnets, while for other media, crews would have to twist a knob and pull drives out of their enclosures and through a magnetic field. To prevent accidental erasure, each technique requires several deliberate steps.
With success in erasing removable media and small hard drives, the researchers are moving onto a final phase of the project, which will involve large computer hard drives partially encased in thick steel caddies.
Beyond Department of Defense applications, the magnetic erasure techniques could have applications to the commercial world, where banks, human resource agencies and other organizations must ensure complete destruction of data in computer equipment being discarded.
Knotts admits he'll be a bit sad to see the project end.
"This was certainly an unusual project," he said. "It's not often that we get paid to crush equipment in presses, blow things up and set off fires in microwave ovens."
John Toon | EurekAlert!
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