Volume 2, Issue 8 October 2002

2002
2001

Comments, questions, suggestions? Send us your feedback by emailing lab-notes@coe.berkeley.edu. September 2002 Good Timing For Nanoscale Atomic Clocks My Arcron wristwatch has a receiver which it uses daily to acquire the signal from the NIST in Fort Collins Colorado. The watch not only uses the data to reset the time but also to recalibrate its oscillator. Rather than try to duplicate the function of the NIST atomic clock, why doesn't professor Pisano's team just develop a receiver to use the NIST signal the way my watch does? The article indicates that the need is primarily for wireless devices that would already be equipped with receivers. If the problem is that not everyone in the world is in range of the Fort Collins signal, wouldn't it be more practical to build more facilities comparable to Fort Collins around the world or to provide some other means for the signal to be received worldwide? It goes without saying that wireless devices won't work at all without some form of radio signal. Even the clock in my wireless cell phone is automatically reset by a radio signal. Based upon having paid only $60 retail for my watch, it would seem that the receiver, oscillator circuitry, and control logic can't be very costly to produce. Also, based upon the tiny battery my watch uses that lasts for years, the power requirements are very low (and most of that power is probably for the elaborate LCD display which includes a time zone map of the world). — Wes Ferguson Response from Professor Albert ('Al') P. Pisano: I fully acknowledges the superiority of the solution that Ferguson proposes, presuming that the accuracy and precision at which time is desired to be known is in the order of a tenth of a second. The real issue is being able to divide time into increments much smaller. Thus, one needs not only an accurate measure of time, but an accurate measure of time to sufficiently small precision. Consider the situation in which you need to know exactly when 10^-6 or 10^-8 of a second goes by (as would be necessary for network packet switching or radio protocols). The Bulova Accutron "beats" at 360 Hertz. That means it only knows time to increments of 2.8*10^-3 seconds. This is three to six orders of magnitude too coarse. The time signal from Fort Collins, likewise, is accurate, but updated much too infrequently to be usable to judge the passage of 10^-8 seconds. It is broadcast on a frequency that is approximately 60 kHz. That would limit the broadcast of the exact time to no more than a few times per second. Likewise, the quartz crystal oscillator in timekeeping equipment beats at approximately 10 kHz, meaning it divides time only into packets that are 10^-4 seconds in size. Again, too coarse a measure. Of course, one could use electronic circuits to generate a frequency reference to divide time into smaller portions. But the limit of these circuits due to their own intrinsic stability is approximately 10^-6 seconds. Again, too coarse, since you could misjudge the time increment by 100%. An atomic clock that would be "moderately" accurate would resolve time to 10^-11 seconds. This is 5 orders of magnitude smaller ... a factor of 100,000. July 2002 Art, Technology, Process, and Product I'm probably not the first to mention that industrial design is a meeting place for many fields of study. ÝEngineering and art are always present and so are ergonomics, human factors, interactive design, business, social and environment. — "APELBOY" Where does engineering meet art? I'll tell you. Robotics. Sculpture. The ability to create a kinetic sculpture with intended movements. So there. — Mark O'Leary Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking research underway today at the College of Engineering that will dramatically change our lives tomorrow. Editor, Director of Public Affairs: Teresa Moore Writer, Researcher: David Pescovitz Designer: Robyn Altman Subscribe or send comments to the Engineering Public Affairs Office: lab-notes@coe.berkeley.edu. © 2002 UC Regents. Updated 9/30/02.