| Sept.
23, 2005
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Nano-devices
May Allow Smaller Microwave Systems
 |
| 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 www.nist.gov/public_affairs/releases/nanooscillators.htm.
* 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.
Advance
May Move Kilogram Closer to 'Natural' Definition
 |
| 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 inquiries@nist.gov.
|
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 www.nist.gov/public_affairs/releases/electrokilogram.htm.
* 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, laura.ost@nist.gov,
(301) 975-4034
NIST
Atomic Fountain Clock Gets Much Better with Time
 |
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 inquiries@nist.gov.
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.
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
www.cirms.org.
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