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New microwave drill is clean, quiet

RAMAT AVIV, Israel, Oct. 17 (UPI) -- Microwaves can do more than just reheat leftovers -- a new, clean, quiet drill from Israel with no spinning parts uses microwaves to bore holes in rock and glass, researchers reported Thursday.

"It penetrates like a hot knife through butter," researcher Eli Jerby, an electrical engineer at Tel Aviv University in Ramat Aviv, told United Press International. "The microwave drill should find use in industry, construction and geology."

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As described in the Oct. 18 issue of the journal Science, the drill bit focuses microwaves at a spot just below the surface of the target using radiation sources similar to those found cheaply in microwave ovens. When matter heats up, its conductivity goes down. This makes it even more likely for microwave-bombarded matter to absorb more microwaves, in what is known as a "thermal runaway" effect.

"It's similar to the effect where the rich have the advantage to get richer and the poor remain poor," Jerby said. "The material gets hotter, and its properties modify so it better absorbs microwaves."

Temperatures in a hotspot the size of a lump of sugar quickly exceed 2,700 degrees Fahrenheit, enough to melt iron. The drill tip then can be pushed into the liquefied matter to form holes only a half-millimeter wide.

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"It is amazing to see how the microwave drill melts hard materials," Jerby said.

The device is limited to a penetration depth of a quarter of the wavelength of the microwaves used -- in this case, about an inch. If the drill bit is any longer, the microwaves are no longer beamed forward but instead radiate in every direction like an antenna.

Still, by pushing the drill bit forward into material, Jerby said this problem can be surmounted to bore holes with no spinning parts, noise or dust. While longer microwave wavelengths could be used, the scientists used cheaper off-the-shelf parts.

The drill works on microwave-absorbent materials such as concrete, glass and ceramic but it is almost ineffective with good conductors such as aluminum and copper. Nevertheless, derivatives of the drill could be used for cutting, nailing, jointing or just local heating.

"Clinical applications might be limited by radiation hazard concerns," Jerby said. "One may conceive, however, medical derivatives of the microwave drills for urgent medical treatments, such as pin insertion into bones.

In addition, the drill could be used as a simultaneous sensor because the hotspot also reflects some microwaves.

"We can use the information in these reflected waves to measure the properties of the material and tune the system to automatically respond to changes to penetrate the material better and faster," Jerby said.

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"The most appealing capability I see with this is the ability to drill relatively small holes, or even possibly fairly precise holes, in ceramics, rocks and glass, without having to worry about replacing drill bits," said electrical engineer John Booske at the University of Wisconsin-Madison. "The question that remains to be seen is whether the potential market will respond."

The work was conducted in a small lab in Israel, so researchers are looking at industry partner to commercialize it.

(Reported by Charles Choi, UPI Science News, in New York)

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