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Atomic clock could land in cell phones

Experimental clock loses only a second every few hundred years--and it could fit in mobile phones and other devices.

Researchers who have built a sugar cube-size atomic clock say their strides in reducing power consumption could one day land the device in cell phones or other machines.

Speaking at the International Solid-State Circuits Conference in San Francisco, Clark Nguyen, a professor at the University of Michigan, provided details on an atomic clock that loses only a millisecond a day or a full second every 274 years.

That's not nearly as good as the NIST-F1, an atomic clock that loses a second once about every 30 million years. However, the F1 takes up about 3.7 cubic meters in volume and requires 500 watts of energy to run.

In contrast, the experimental atomic clock, developed in coordination with the Defense Advanced Research Projects Agency and the National Institute of Standards and Technology, only takes up about a cubic centimeter of volume and runs on about 75 milliwatts, which can be provided by ordinary batteries.

The ultimate goal is to increase accuracy while reducing power consumption to 30 milliwatts, Nguyen said.

Miniature, energy-efficient atomic clocks could help improve the performance of a number of devices because signals could be more easily coordinated. A cell phone could acquire signals much more rapidly, as well as block out unwanted signals. The Global Positioning System now can take minutes to acquire the necessary signals to pinpoint location.

Accurate timing enables more precise measurements of distance. And if it takes less time for a signal to go from a satellite to a receiver, less battery power is used.

"With an atomic clock, it will take one second," Nguyen said. Energy efficiency is, in part, a by-product of miniaturization. The clock keeps time by monitoring cesium atoms, which click between different energy states with the regularity of a metronome. The cesium vapor has to be heated to 80 degrees Celsius.

If the vapor chamber were 2 centimeters long, it would take 15 minutes and 15 watts of energy to hit those temperatures. The vapor chamber in the experimental clock, however, is 0.6 square millimeters in volume and takes more than 3 seconds and a few milliwatts to get to 80 Celsius.

Additionally, buffer gases are contained in the chamber to reduce energy lost in collisions between cesium and the chamber walls.