NANO: Casimir force a source of energy/propulsion?

From: Mike Lorrey (
Date: Thu Jan 24 2002 - 12:03:06 MST

It seems that some researchers, including some at NASA, are researching
the use of MEMS devices to extract energy from Zero Point Field quantum

According to classical physics, a vacuum at a temperature of absolute
zero contains no matter or energy. But according to quantum physics,
this emptiness isn't really empty. It is filled with fluctuating energy.

Classical physics, as epitomized by Newton's laws, describes how matter
and energy operate in the everyday world. Quantum physics describes the
very different conditions that exist in the realm of atoms and subatomic

A team at Lucent Technologies' Bell Labs has shown that as researchers
make ever smaller machines, the quantum effect of zero point energy
could come into play. The researchers built a microelectromechanical
device similar to those used as tiny sensors and actuators, and measured
how this energy affected it.

Zero point energy is created by subatomic particles that appear out of
nothing, then rapidly disappear. Because many of the particles are
photons, much of the energy is electromagnetic like light, x-rays and
radio waves. "This energy pervades all space. It's everywhere," said Ho
Bun Chan, a physicist at Bell Labs.

The energy becomes a factor in the world of devices when two parallel
plates are positioned closely enough that the gap between them is
smaller than some electromagnetic wavelengths. This means that 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.

The phenomenon, predicted in 1948 by the Dutch physicist Hendrik
Casimir, observed in 1958 and measured in 1996, is called the Casimir
effect. "This force arises merely because of the existence of the two
plates," said Chan.

Though the force is very small at the micro scale, it increases rapidly
as the distance between the plates decreases. The force between parallel
plates can be as large as an atmosphere, or 14.7 pounds per square inch
of pressure, at a distance of 10 nanometers, said Umar Mohideen, an
associate professor of physics at the University of California at

The Bell Labs' device consists of a 500-micron-square, 3.5-micron thick
silicon plate suspended above a silicon wafer. The plate pivots, seesaw
fashion, between two tiny rods. Electrodes sit on the wafer under each
end of the seesaw. As the plate tilts, the capacitance on the lower side
increases while that of the higher side decreases, allowing the
researchers to measure very small changes in the position of the plate.

The researchers induced the Casimir effect in their device by lowering a
200-micron-diameter sphere over the plate. "When the plate is actuated
by the Casimir force, the rotation is only about a thousandth of a
degree. It's a tiny rotation, but it's detectable," said Chan.

The Bell Labs research "is the first step in the design and fabrication
of novel MEMS devices based on the Casimir force," said Mohideen.
"Finally, devices based on quantum fluctuations... are coming to
fruition. This is very exciting."

The researchers used a sphere rather than a second plate because it's
easier to work with even though the Casimir effect is less pronounced
between a sphere and a plate, said Chan.

"We are talking about separations [of] less than a tenth of a
micrometer," he said. "It's very difficult to keep two plates perfectly
parallel. If you use a sphere there's only one point where it's closest
to the plate. It basically gets rid of the alignment problem," he said.

The plate tilted due to the Casimir effect when the sphere was 300
nanometers above one end of the plate. The tilt increased sharply as the
researchers moved the sphere closer to the plate.

"We can speculate [about] making very sensitive position sensors, for
example, because this force rises very quickly with distance," said

As Bell Labs' use of a sphere illustrates, the effect is not limited to
parallel plates.

"The Casimir force is strongly shape dependent and can be repulsive as
well as attractive," said Mohideen. "It can be further modified with
subtle texturing on the surfaces, like putting in corrugations.
Incorporating the shape-dependent Casimir force should give an
additional knob for engineers to turn in future MEMS designs," he said.

A NASA-funded project is even exploring how to use the Casimir effect in
a propulsion system for spacecraft.

The Casimir effect is already a problem for fabricating MEMS devices
because at very short distances free surfaces tend to stick together,
said Mohideen. "During the fabrication step, it is very hard to make
free moving surfaces such as cantilevers [and] bridges which are
separated by short distances," he said.

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