DARPA develops portable atomic clock

The Defense Advanced Research Projects Agency has developed a portable atomic clock that could free many military electronic devices from continual use of global positioning system satellite signals, said Clark Nguyen, the DARPA program manager overseeing the project.

More accurate time-keeping devices also could sharpen precision in surveillance, missile guidance and communications devices.

'Our best military electronic systems is often limited by the performance of the clocks they use,' Nguyen said at the DARPATech conference last week in Anaheim, Calif.

Nguyen said a DARPA team has actually produced a portable atomic clock, though further refinements in power performance and stability are still needed.

Atomic clocks provide extremely accurate measurements of time. The National Institute of Standards and Technology and the Naval Observatory use the atomic clock-generated time at the Time.gov Web site. The site claims its time never differs more than 0.0000001 seconds from the Coordinated Universal Time, the international time standard.

Atomic clocks function similarly to quartz-based clocks, Nguyen said. Quartz clocks rely on a steady frequency generated by a quartz oscillator to gauge the passage of time. But this frequency eventually can drift due to stress and mechanical limitations. In contrast, an atomic clock 'derives its frequency from the energy difference between the hyperfine states of an alkali metal atom, which is a constant of nature, and ' much more predictable and stable,' Nguyen said.

Traditionally, atomic clocks have been very large. A large amount of alkali metal is needed in the devices, and must be heated in order to be effective. DARPA's approach is to shrink the atomic cell to less than 10 cubic millimeters, reducing the power needed to heat the element.

A portable atomic time-keeping element could reduce the need for GPS signals in many devices, Nguyen said. GPS devices use time signals from satellites to coordinate positions. If a GPS signal is jammed or otherwise lost, an atomic clock-based device could switch to internally generated time. Atomic clock timing also could enable more robust wireless networking, as it could facilitate ultra-fast frequency hopping rates, Nguyen said.

About the Author

Joab Jackson is the senior technology editor for Government Computer News.

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