force powers microslide
Technology Research News
Researchers have coaxed two tiny metal
parts to slide past each other powered only by the shapes of the parts
and an oddity of quantum physics. The effect could be used to move microscopic
According to quantum physics, a vacuum is actually seething with zero-point
energy, which is created by subatomic particles constantly popping in
and out of existence. Many of the particles are photons, which means much
of the energy is electromagnetic like light, x-rays and radio waves.
When two parallel plates are positioned closely enough that the gap between
them is smaller than some electromagnetic wavelengths, some of the zero-point
energy is shut out of the gap. Because there is more zero-point energy
acting on the outer surfaces of the plates than the inner surfaces, the
plates are drawn together, a phenomenon termed the Casimir effect.
Researchers at the University of California at Riverside and the Federal
University of Paraíba in Brazil have found a way to use this effect to
cause one surface to slide over another.
"The normal Casimir force acts perpendicular to the two interacting surfaces,
pulling them together," said Umar Mohideen, an associate professor of
physics at the University of California at Riverside. "The lateral Casimir
force acts tangential to the two surfaces, leading to the horizontal sliding
of one surface with respect to the other," he said.
In theory, if two corrugated plates are aligned parallel to each other
and positioned closely enough, the Casimir force will come into play.
But unlike two flat plates that are drawn together, the corrugated surfaces
are at angles to the plate as a whole, and so when the surfaces are drawn
together they move the plates laterally.
Because it is very difficult to keep two plates perfectly parallel when
they are separated by less than a micron, the researchers replaced one
of the plates with a gold sphere one-fifth of a millimeter in diameter.
The researchers imprinted the sphere with corrugations by pressing the
plate into it.
The researchers moved the plate sideways less than half a nanometer at
a time and measured the lateral force exerted on the sphere at each step.
A nanometer is one millionth of a millimeter. The researchers started
with the plate and sphere separated by 221 nanometers. They increased
the distance between them in 12 nanometer increments and repeated the
lateral steps at each distance. As expected, the Casimir effect weakened
as the distance increased.
The researchers are studying other shapes to use in their next experiment,
said Mohideen. "The Casimir force depends strongly on the shape of the
[surfaces] and can be repulsive or attractive," he said. "The force between
two parallel metallic plates is attractive, [but] that between two hemispheres
systems (MEMS) become smaller, the Casimir effect could gum up the
works. But researchers could also harness the effect. The lateral Casimir
force could be used to provide sliding motion, said Mohideen.
The lateral Casimir effect is not surprising, said Steve Lamoreaux, a
physicist at the Los Alamos National Laboratory. "[However], the experiment
must have been extremely difficult and as such the result represents a
real tour de force, no pun intended. This effect might be useful in nano-machines;
it could be used as a lateral spring of some sort," he said.
"On the other hand, there is also a large force between the surfaces trying
to pull them together, so there is a limitation on the usefulness of the
effect," Lamoreaux said.
The lateral Casimir force could be applied in MEMS technology now but
it is likely to take five to ten years before practical devices make use
of it, said Mohideen.
Mohideen's research colleagues were Feng Chen of the University of California
at Riverside, and Galina Klimchitskaya and Vladimir Mostepanenko of the
Federal University of Paraíba in Brazil. They published the research in
the March 11, 2002 issue of the journal Physical Review Letters. The research
was funded by the National Science Foundation (NSF), the National Institute
of Standards and Technology (NIST) and the Brazilian government.
Timeline: 5-10 years
TRN Categories: Microelectromechanical Systems (MEMS);
Story Type: News
Related Elements: Technical paper, "Demonstration of the
Lateral Casimir Force," Physical Review Letters, March 11, 2002
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