Microwaves Pierce Painlessly

Holier than thou. Microwaves promise clean, silent drilling at a fraction of the cost of lasers.

Anyone unfortunate enough to remain awake in the dentist's chair may be acutely aware of the drawbacks of a spinning mechanical drill: noise, vibration, and flying debris. The drill bit feels the pain, too, eventually wearing out or breaking under the repeated stress. Now, researchers have developed a drill that uses microwave energy to excavate solids. The new drill is silent, steady, and dust-free, and the bits almost never wear out.

Drilling with electromagnetic radiation is nothing new. For years, engineers and scientists have been using tightly focused lasers to punch tiny holes in everything from silicon chips to human bone. But laser drills are expensive, and a several-hundred-thousand-dollar laser might not always be the right tool to quietly put a 1-millimeter-wide hole in a concrete block.

So a Tel Aviv University team led by mechanical engineer Eliyahu Jerby cooked up a low-cost alternative. "We pulled the magnetron from a domestic microwave oven," Jerby says. "It cost about $20." To focus the microwaves, radiation from the magnetron is directed into a metal box that guides the radiation into one end of a piece of coaxial cable. The other end of the cable is placed near the surface where the hole will be drilled. Using a mirror, the researchers can direct the microwave energy to travel into a spot just under the surface instead of being reflected. As that spot starts to heat up, changes in the material cause that spot to soak up even more energy. A drill bit passing down the center of the cable can then easily scoop out the molten material. Jerby's team has already used a drill prototype to put holes with diameters ranging from about 1 millimeter to 1 centimeter in ceramics, concrete, basalt, glass, and silicon. The team reports the work in the 18 October issue of Science.

"The cool thing is that you can drill without wear, breakage, or cracking the tool bit," says electromagnetic scientist John Booske of the University of Wisconsin, Madison. But don't expect to see the microwave drill during your next dental checkup. Although the lab model emits less radiation than a typical home microwave oven, Jerby says, "safety is still a big concern." Production models of the drill will either be completely enclosed or use a shielding plate.

Related sites
What are microwaves?
All about microwave ovens
Eliyahu Jerby's page
John Booske's page

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