The Chip Scale Atomic Clock makes atomic time-keeping portable
By Ben Coxworth
May 6, 2011
Atomic clocks are one of those things that most of us have probably always thought of as being big, ultra-expensive, and therefore only obtainable by well-funded research institutes. While that may have been the case at one time, a team of researchers have recently developed an atomic clock that they say is one one-hundredth the size – and that uses one one-hundredth the power – of previous commercially-available products. It's called the Chip Scale Atomic Clock (CSAC), and it can be yours for about US$1,500 ... a little more than what you might pay for a regular clock, but not bad for one that varies by less than a millionth of a second per day.
The device is about the size of a matchbox, and operates on just 100 milliwatts, drawn from two AA batteries. By contrast, some much larger traditional "portable" atomic clocks need to be hooked up to a car battery.
Incorporated within the CSAC is a rice-grain-sized container, developed by Draper Laboratory, that contains cesium atoms. Two layers of steel sheathing keep them from being affected by the Earth's electromagnetic fields. The atoms are struck by the beam of a vertical-cavity surface-emitting laser (VCSEL), made by Sandia National Laboratories, causing them to regularly emit microwaves. While traditional atomic clocks use a more power-hungry rubidium laser, the VCSEL uses just two milliwatts.
Finally, the clock's circuitry (designed by Symmetricom Inc.) measures time by counting the frequency of the microwaves – exactly 4,596,315,885 of them constitute one second.
One thing the CSAC doesn't do, however, is keep track of the time of day. Instead, it's intended mainly for use with other atomic clocks, allowing two or more geographically-separated groups of people to stay exactly coordinated over time.
These groups could include miners in underground tunnels, divers in the deep ocean, or other people who are physically blocked from receiving time signals by GPS. Security personnel disarming improvised explosive devices could also use the technology, as the electromagnetic interference that they utilize to keep telephone signals from detonating the explosives also disables GPS devices. Additionally, CSACs could find use in cross-country phone and data lines, allowing the various data packets to stay coordinated in the event of a GPS outage.
While there are various small, inexpensive devices already being sold as "atomic clocks," these simply display a signal received from a remote atomic clock. If you want the real thing, and have $1,500 to spare, you can order a CSAC from the Symmetricom website.
Development of the clock was funded by DARPA, the Defense Advanced Research Projects Agency.