SPARE parts from a microwave oven can now be used to drill holes in brittle materials such as ceramics, glass and concrete. The new technique neatly fills a niche between mechanical and laser drilling.
While mechanical drills are cheap, they don’t work well on hard, brittle materials. Laser drills, on the other hand, produce small holes very accurately without mechanical contact, but are very expensive. The microwave option, says inventor Eli Jerby of Tel Aviv University in Israel, would come somewhere in between.
The trick is to combine a microwave antenna with a drill bit that doesn’t have to turn. Microwaves passing down the antenna heat up the material being drilled. This softens it enough for the bit to push through easily, says Jerby (Science, vol 298, p 587).
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Jerby and his colleagues made their drill using a cavity magnetron – the same device that generates 12-centimetre wavelength microwaves in a microwave oven. The team steered the radiation from the cavity magnetron down a short metal tube with a tungsten drilling rod running down its centre (see Diagram). The tube acts as a waveguide, focusing the microwaves onto the target material, where they heat up a spot between a millimetre and a centimetre across.
As the material heats up it absorbs more radiation, eventually reaching “thermal runaway” – when the material is soft enough for the central rod to be pushed through it. So far, Jerby and his colleagues have tested the drill on materials such as concrete, basalt, glass and silicon.
Because the microwave drill works only on materials that absorb microwaves, it does not work on metals, which reflect them. Despite this drawback, the microwave drill offers other advantages over mechanical versions. For example, many of the materials it has been testedon are usually hard to drill mechanically.
But you are unlikely to be using a microwave drill around the house, since strong microwave radiation can dangerously heat living tissue. Jerby expects microwave drills will first be used on automated production lines, but could also be used for construction and geological drilling. He already has a US patent on the drill, and is looking at applications in cutting and welding.