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Sept. 23, 2005

  In This Issue:
bullet Nano-devices May Allow Smaller Microwave Systems

Advance May Move Kilogram Closer to 'Natural' Definition

bullet NIST Atomic Fountain Clock Gets Much Better with Time
  Quick Links:
bullet Meeting on New Technologies and Radiation Measurements

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Nano-devices May Allow Smaller Microwave Systems

simulation shows wave patterns from two adjacent nano-oscillators
A simulation made with NIST micromagnetic software shows the interaction of "spin waves" emitted by two nano-oscillators that generate microwave signals. The ability of these tiny spintronic devices to spontaneously synchronize their emissions may lead to smaller, cheaper wireless communications components.

Credit: NIST

View a high-resolution version of this image.

Like the flashing of fireflies and ticking of pendulum clocks, the signals emitted by multiple nanoscale oscillators can naturally synchronize under certain conditions, greatly amplifying their output power and stabilizing their signal pattern, according to scientists at the National Institute of Standards and Technology (NIST).

In the Sept. 15 issue of Nature,* NIST scientists describe “locking” the dynamic magnetic properties of two nanoscale oscillators located 500 nanometers apart, boosting the power of the microwave signals given off by the devices. While an individual oscillator has signal power of just 10 nanowatts, the output from multiple devices increases as the square of the number of devices involved. The NIST work suggests that small arrays of 10 nano-oscillators could produce signals of 1 microwatt or more, sufficient for practical use as reference oscillators or directional microwave transmitters and receivers in devices such as cell phones, radar systems and computer chips.

“These nanoscale oscillators could potentially replace much bulkier and more expensive components in microwave circuits,” says Matthew Pufall, one of the NIST researchers. “This is a significant advance in demonstrating the potential utility of these devices.”

The NIST-designed oscillators consist of a sandwich of two magnetic films separated by a non-magnetic layer of copper. Passing an electrical current through the device causes the direction of its magnetization to switch back and forth rapidly, producing a microwave signal. The circular devices are 50 nanometers in diameter, about one-thousandth of the width of a human hair and hundreds of times smaller than the typical microwave generators in commercial use today. The devices are compatible with conventional semiconductor technology, which is expected to make them inexpensive to manufacture.

The type of signal locking observed at NIST was first described by the 17th-century Dutch scientist Christiaan Huygens, who found that two pendulum clocks mounted on the same wall synchronized their ticking, thanks to weak coupling of acoustic signals through the wall. This phenomenon also occurs in many biological systems, such as the synchronized flashing of fireflies, the singing of certain crickets, circadian rhythms in which biological cycles are locked to the sun, and heartbeat patterns linked to breathing speed. There are also examples in the physical sciences, such as the synchronization of the moon’s rotation with respect to its orbit about the Earth.

For further information, see

* S.F. Kaka, M.R. Pufall, W.H. Rippard, T.J. Silva, and S.E. Russek. 2005. Mutual Phase-Locking of Microwave Spin Torque Nano-Oscillators. Nature. Sept. 15.

Media Contact:
Laura Ost,, (301) 975-4034



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Advance May Move Kilogram Closer to 'Natural' Definition

Scientist load kilogram mass into the NIST watt balance apparatus
Physicist Richard Steiner adjusts the electronic kilogram, an experimental apparatus for defining mass in terms of the basic properties of nature.

©Robert Rathe

For a high-resolution version of this photo contact

A leading experimental method for defining the kilogram in terms of properties of nature is now more accurate than ever, scientists at the National Institute of Standards and Technology (NIST) reported on Sept. 13. The advance may move the scientific community closer to redefining the kilogram, the only one of the seven basic units of the international measurement system still defined by a physical artifact.

The latest NIST work, described in the October 2005 issue of Metrologia* and published online Sept. 13, confirms the institute’s 1998 results using the same method while reducing the measurement uncertainty by about 40 percent, thanks mainly to improvements in the hardware used in the experiments.

“The fact that we got the same values gives us confidence that the uncertainties we’re quoting are probably reasonable,” says NIST physicist Richard Steiner, lead author of the paper.

Scientists at NIST and other institutions around the world have spent years conducting experiments to find a reliable definition based in nature to replace the current international standard for the kilogram, a century-old cylinder of platinum-iridium alloy about the size of a plum. The new results mean that the NIST method, using an apparatus called the watt balance or electronic kilogram, is almost accurate enough now to meet the criteria for redefinition.

Any decision about when and how to redefine the kilogram would be made by an international group, the International Committee for Weights and Measures, CIPM, and ratified by a General Conference on Weights and Measures (CGPM), which next meets in 2007. The CGPM likely will delay a redefinition until other groups confirm the new NIST results.

The NIST watt balance is a two-story-high apparatus designed to redefine mass in terms of fundamental physics and quantum standards. It measures the force required to balance a 1-kilogram mass artifact against the pull of Earth’s gravity, as well as two electrical values. These measurements are used to determine the relationship between mechanical and electrical power, which can be combined with several equations to define the kilogram in terms of basic properties of nature.

For further information, see

* R. Steiner, E.R. Williams, D.B. Newell and R. Liu. “Towards an electronic kilogram: an improved measurement of the Planck constant and electron mass.” Metrologia. 42 (2005) 431-441. Published online Sept. 13, 2005.

Media Contact:
Laura Ost,, (301) 975-4034



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NIST Atomic Fountain Clock Gets Much Better with Time

Three scientists with the NIST F1 atomic clock

NIST researchers (left to right) Steven Jefferts, Elizabeth Donley, and Tom Heavner with NIST F1, the world's best clock (as of Sept. 2005). The clock uses a fountain-like movement of cesium atoms to determine the length of the second so accurately that—if it were to run continuously—it would neither lose nor gain one second in 60 million years.

© 05 Geoffrey Wheeler Photography

For a high-resolution version of this photo contact An additional version of this photo showing just the F1 atomic clock is also available.

The world’s best clock, NIST-F1, has been improved over the past few years and now measures time and frequency more than twice as accurately as it did in 1999 when first used as a national standard, physicists at the National Institute of Standards and Technology (NIST) report.

The improved version of NIST-F1 would neither gain nor lose one second in 60 million years, according to a paper published online Sept. 13 by the journal Metrologia.* NIST-F1 uses a fountain-like movement of cesium atoms to determine the length of the second. The clock measures the natural oscillations of the atoms to produce more than 9 billion "ticks" per second. These results then contribute to the international group of atomic clocks that define the official world time. NIST-F1 has been formally evaluated 15 times since 1999; in its record performance, it measured the second with an uncertainty of 0.53 × 10-15

The improved accuracy is due largely to three factors, according to Tom Parker, leader of the NIST atomic standards research group. First, better lasers, software and other components have made the entire NIST-F1 system much more reliable and able to operate for longer periods of time. Second, the atoms in the cesium vapor are now spread out over a much larger volume of space, reducing the frequency shifts caused by interactions among the atoms. (The formerly round cloud of atoms is now shaped like a short cigar.) Third, scientists are now better able to control magnetic fields within the clock and quantify the corrections needed to compensate for their effects on the atoms.

Improved time and frequency standards have many applications. For instance, ultraprecise clocks can be used to improve synchronization in precision navigation and positioning systems, telecommunications networks, and wireless and deep-space communications. Better frequency standards can be used to improve probes of magnetic and gravitational fields for security and medical applications, and to measure whether “fundamental constants” used in scientific research might be varying over time—a question that has enormous implications for understanding the origins and ultimate fate of the universe.

* T.P. Heavner, S.R. Jefferts, E.A. Donley, J.H. Shirley, T.E. Parker. 2005. NIST-F1: Recent improvements and accuracy evaluations. Metrologia (October 2005). Posted online Sept. 13.

Media Contact:
Laura Ost,, (301) 975-4034



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Quick Links

Meeting on New Technologies and Radiation Measurements

The impact of new technologies on radiation measurements and standards will be the focus of the 14th annual conference of the Council on Ionizing Radiation Measurements and Standards, to be held Oct. 24-26, 2005, at the National Institute of Standards and Technology in Gaithersburg, Md. The purpose of the conference is to identify the common needs of industry, government and academic institutions for ionizing radiation measurements and standards. Presentations will focus on the impact of new technologies on radiation measurement needs in areas such as health care, materials for radiation detection, devices generating or using radiation, and information on the effects of radiation and approaches being considered to respond to radiological emergencies. The agenda and online registration are available at



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Editor: Gail Porter

Date created: 9/23/05
Date updated: 9/23/05