Sticky tape and terahertz radiation

02 August 2009

SELLOTAPE

Reel of sticky tape

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Unwinding sticky-tape produces terahertz waves that might play a useful role in airport security...

It has been known for a long time that if you unwind sticky tape in the dark you can sometimes see flashes of light, we did a kitchen science on this subject a few months ago.

In the last year or so it has been discovered that if you unwind sticky tape in a vacuum you can generate enough x-rays to take a photograph of bones. This is thought to happen, because when you unpeel the tape, one side ends up positively charged and the other negative. In air sparks can jump between the two giving off light, and in a vacuum, electrons accelerate until they hit the other side giving off X-rays.

You would have thought that this was enough for something more often found in an office than a lab, but Joseph Horvat and Roger Lewis, of the University of Wollongong in New South Wales, thought that sticky tape had more to give. So they had a look at unwinding the tape with a terahertz sensor.

Terahertz rays are a type of light between the infrared and microwaves, which, until very recently, we had no way of producing or studying. They have lots of interesting properties, including the ability to look through clothes to see hidden weapons, and it would appear that they are produced by sticky tape.

The researchers think the radiation is caused by charged ions moving between the two pieces of tape and then decelerating. At the moment they have produced only 1 microwatt of power, which is not very useful, but they think they may be able to improve the efficiency by optimising the tape, the speed and the gas it is sitting in.

Whether airport scanners will be powered by sticky tape in the future I don't know but sticky tape is turning out to be far more interesting than anyone could have imagined.

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