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Working with a package supplier in Berlin, the team is building a 1D accelerometer before moving to a 3D version. The researchers predict a commercial chipscale 1D quantum accelerator will be possible in the next three years, with a 3D sensor within five years. Other researchers at NPL are also using hollow fibres filled with caesium atoms to create miniature atomic clocks. These can provide high accuracy for navigation systems in small, light packages. Such a system could provide 10 days support in the event of a GPS failure. The precision relates to the rate of “ticking” of the clock which is provided by the natural frequency of the electronic transitions in the atoms used. Higher frequencies allow time to be divided into smaller units while the accuracy of a clock is related to systematic errors in its operation and the degree to which these errors can be successfully corrected. These errors include factors due to atomic collisions, the Zeeman Fig. 4: Types of atomic clocks (source: Prof Patrick Gill, NPL). effect of magnetic fields, interaction with black body radiation and the Doppler effect. Finally, there is a gravitational element to the design, as General Relativity causes a difference in the flow of time. A height reduction of 1m at “sea level” is approximately equivalent to a 10-16 change in frequency, which is now the level of accuracy these devices can achieve. The stability of a clock, its capability to deliver a frequency reference unchanging over the specified time interval, is a measure of the tendency of a clock’s rate to vary, perhaps because of a changing environment. The more accurate and stable the underlying technology, the smaller a clock can be made for a given accuracy and the less dependence there is on the GPS satellite system. The importance of accurate timing is shown by a team at consultancy Plextek in Cambridge that is working on a scheme to use more accurate timing for groups of unmanned underwater vehicles. By exchanging estimates of position and the time of flight, the accuracy of the position of each UUV can be improved significantly. This is complicated by the non-linear time of flight of signal underwater, but helps improve the detection of mines and other underwater threats. The UK’s Technology Strategy Board (TSB) is planning a multimillion pound funding call in September to boost the development of such quantum sensors and clocks. www.electronics-eetimes.com Electronic Engineering Times Europe June 2014 11


EETE JUN 2014
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