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Atomic clock gets mini-makeover

By Simon Hooper for CNN

John Kitching
NIST physicist John Kitching led the team that built the clock.
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(CNN) -- Punctuality-phobes may soon no longer be able to blame perennial lateness on slow-running watches following the invention of an atomic clock small enough to wear on your wrist.

Scientists at the National Institute for Standards and Technology in Boulder, Colorado, have taken portable time keeping to new levels of accuracy with the creation of the device, which is driven by inner workings barely bigger than a grain of rice.

The complete working clock would be sugar cube-sized and would run on just 73 milliwatts -- small enough for it to be incorporated into battery-powered handheld devices such as mobile phones.

The clocks currently used in most electronic devices are based on quartz oscillators, in which minute vibrating quartz crystals produce precise pulses. But their accuracy can be adversely affected by factors such as temperature.

By contrast, the atomic clock would be accurate to within a second every 300 years, making it more than 1,000 times more reliable than a very good wristwatch.

Although still a long way short of the levels of precision achieved by larger atomic devices, which vary less than a second over millions of years, the miniature model has other factors in its favor.

Atomic clocks can be several meters tall, expensive to build and power-hungry, making them extremely impractical for commercial use. As well as being tiny by comparison, the new model is based on the same cost-efficient manufacturing techniques used to build microchips.

NIST scientists also expect to substantially improve the clock's long-term stability and reduce its power consumption.

"The real power of our technique is that we're able to run the clock on so little electrical power that it could be battery operated and that it's small enough to be easily incorporated into a cell phone or some other kind of handheld device," said NIST physicist John Kitching.

"And nothing else like it even comes close as far as being mass producible."

Atomic clocks work by measuring the frequency of cesium atoms, which vibrate almost 9.2 billion times a second. An infrared laser pulsed through them is converted into an electrical signal by a photo cell.

In the miniature version, a tiny amount of cesium vapor -- containing about one billion atoms -- is trapped in a silicon cell.

Although much cheaper to produce than the most accurate quartz oscillators, at around $100 the atomic clock may still be too expensive to attract the attention of electrical manufacturers. But its designers believe costs may fall in the same way that microchip prices have plunged.

Beyond making possible a new generation of extremely accurate electrical devices, the clock also has the potential to improve the security and performance of wireless communications devices, by enhancing network synchronization and channel selection.

It could also radically improve the precision of Global Positioning System satellite-based navigation devices.

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