|March 21, 2000
Media Contact: Kim
McDonald (858) 534-7572
UCSD PHYSICISTS DEVELOP
NEW CLASS OF COMPOSITE MATERIALS WITH
'REVERSED' PHYSICAL PROPERTIES NEVER BEFORE SEEN
Minneapolis, MN-Physicists at
the University of California, San Diego have produced a new class of
composite materials with unusual physical properties that scientists
theorized might be possible, but have never before been able to
produce in nature.
The remarkable achievement,
detailed in a paper that will appear in a forthcoming issue of
Physical Review Letters, was announced here today at a meeting of the
American Physical Society. The UCSD physicists said they expect their
discovery to open up a new subdiscipline within physics and produce an
array of commercial applications for this material, on which the
university has applied for a patent.
"Composite materials like
this are built on a totally new concept," said the two co-leaders
of the UCSD team, Sheldon Schultz and David R. Smith, who announced
their discovery at a news conference. "While they obey the laws
of physics, they are predicted to behave totally different from normal
materials and should find interesting applications."
The unusual property of this
new class of materials is essentially its ability to reverse many of
the physical properties that govern the behavior of ordinary
materials. One such property is the Doppler effect, which makes a
train whistle sound higher in pitch as it approaches and lower in
pitch as it recedes. According to Maxwell's equations, which describe
the relationship between magnetic and electric fields, microwave
radiation or light would show the opposite effect in this new class of
materials, shifting to lower frequencies as a source approaches and to
higher frequencies as it recedes.
Similarly, Maxwell's equations
further suggest that lenses that would normally disperse
electromagnetic radiation would instead focus it within this composite
material. This is because Snell's law, which describes the angle of
refraction caused by the change in velocity of light and other waves
through lenses, water and other types of ordinary material, is
expected to be exactly opposite within this composite.
"If these effects turn out
to be possible at optical frequencies, this material would have the
crazy property that a flashlight shining on a slab can focus the light
at a point on the other side," said Schultz. "There's no way
you can do that with just a sheet of ordinary material."
He notes that the development
of this new class of materials, which was financed by the National
Science Foundation and the Department of Energy, is entirely
consistent with the laws of physics and was predicted as a possibility
in 1968 by a Russian theorist, V.G. Veselago. "But until
now," Schultz adds, "no one had the material, so it couldn't
Underlying the reversal of the
Doppler effect, Snell's law, and Cerenkov radiation (radiation by
charged particles moving through a medium) is that this new material
exhibits a reversal of one of the "right-hand rules" of
physics which describe a relationship between the electric and
magnetic fields and the direction of their wave velocity.
The new materials are known by
the UCSD team colloquially as "left-handed materials," after
a term coined by Veselago, because they reverse this relationship.
What that means is physically counterintuitive-pulses of
electromagnetic radiation moving through the material in one direction
are composed of constituent waves moving in the opposite direction.
The UCSD physicists emphasized
that while they believe their new class of composites will be shown to
reverse Snell's law, the specific composite they produced will not do
so at visible-light frequencies. Instead, it is now limited to
transmitting microwave radiation at frequencies of 4 to 7 Gigahertz-a
range somewhere between the operation of household microwave ovens
(3.3 Gigahertz) and military radars (10 Gigahertz).
However, Schultz said the UCSD
team will soon be attempting to verify that a composite constructed on
similar principles will be able to focus and disperse microwaves in
exactly the opposite manner as normal lenses. "We did not do this
experiment yet," he said. "But this is what the equations
predict. Physicists will understand that if our data presented in our
paper are correct, given Maxwell's equations, then this will be the
The composite constructed by
the UCSD team-which also consisted of Willie J. Padilla, David C. Vier,
and Syrus C. Nemat-Nasser-was produced from a series of thin copper
rings and ordinary copper wire strung parallel to the rings. It is an
example of a new class of materials scientists call "metamaterials."
"Even though it is composed of only copper wires and copper
rings, the arrangement has an effective magnetic response to
microwaves that has never been demonstrated before," said
The idea for the new composite
came from Smith, building on the work of John Pendry of Imperial
College, London. In 1996, Pendry described a way of using ordinary
copper wires to create a material with the property physicists call
"negative electric permittivity." Electric permittivity-often
referred to as the "dielectric constant"-is the response of
a material to electromagnetic radiation.
"When you take a material
like plastic, glass or sapphire and you shine microwaves onto it, you
can characterize how the microwaves going through it will behave by a
parameter called electric permittivity," explained Schultz. Most
known materials in nature have a positive electric permittivity.
Pendry also recently suggested
a way of using copper rings to make a material with negative magnetic
permeability at microwave frequencies. Just about all of the magnetic
materials in nature, those that respond to magnetic rather than
electric fields, have what physicists call a "positive magnetic
What's unusual about the new
class of materials produced by the UCSD team is that it simultaneously
has a negative electric permittivity and a negative magnetic
permeability, a combination of properties never before seen in a
natural or man-made material.
"And the interesting thing
is that it's produced with no magnetic material," said Schultz.
"It's all done with copper."
"The bottom line,"
said Smith, "is that this material-this metamaterial, at
frequencies where both the permittivity and permeability are negative,
behaves according to a left-handed rule, rather than a right-handed
# # #
David Smith can be reached
March 20-22 in Minneapolis at 612-331-1900.
Sheldon Schultz can be reached
March 20-23 in Minneapolis at 612-333-4545
Messages for the UCSD
scientists can also be left at the APS meeting pressroom at
612-335-6735, 6736, 6737, 6738. Pressroom Hours: Mon.-Wed. 8AM to 5PM,
Thurs. 8AM to noon. The news conference will take place at 1 p.m.
March 21 at the Minneapolis Convention Center, Room 203B.