Home' Technology Review : March April 2007 Contents 56 TR10
TECHNOLOGY REVIEW /
The announcement last November
of an "invisibility shield," created
by David R. Smith of Duke Uni-
versity and colleagues, inevitably set the
media buzzing with talk of H. G. Wells s
invisible man and Star Trek s Romulans.
Using rings of printed circuit boards, the
researchers managed to divert micro-
waves around a kind of "hole in space";
even when a metal cylinder was placed
at the center of the hole, the microwaves
behaved as though nothing were there.
It was arguably the most dramatic
demonstration so far of what can be
achieved with metamaterials, compos-
ites made up of precisely arranged pat-
terns of two or more distinct materials.
These str uctures can manipulate electro-
magnetic radiation, including light, in
ways not readily obser ved in nature. For
example, photonic crystals---arrays of
identical microscopic blocks separated
by voids---can re ect or even inhibit the
propagation of certain wavelengths of
light; assemblies of small wire circuits,
like those Smith used in his invisibility
shield, can bend light in strange ways.
But can we really use such materials
to make objects seem to vanish? Philip
Ball spoke with Smith, who explains
why metamaterials are literally chang-
ing the way we view the world.
TR: How do metamaterials let you make
Smith: It s a somewhat complicated
procedure but can be very simple to
visualize. Picture a fabric formed from
inter woven threads, in which light is
constrained to travel along the threads.
Well, if you now take a pin and push
it through the fabric, the threads are
distorted, making a hole in the fabric.
Light, forced to follow the threads, is
routed around the hole. John Pendry
at Imperial College in London calcu-
lated what would be required of a meta-
material that would accomplish exactly
this. The waves are transmitted around
the hole and combined on the other side.
So you can put an object in the hole, and
the waves won t "see" it---it s as if they d
crossed a region of empty space.
And then you made it?
Yes---once we had the prescription,
we set about using the techniques we d
developed over the past few years to
make the material. We did the experi-
ment at microwave frequencies because
the techniques are very well estab-
lished there and we knew we would
be able to produce a demonstration
quickly. We printed millimeter-scale
metal wires and split rings, shaped
like the letter C, onto berglass cir-
cuit boards. The shield consisted of
about 10 concentric cylinders made up
of these split-ring building blocks, each
with a slightly di erent patter n.
So an object inside the shield is actually
More or less, but when we talk about
invisibility in these str uctures, it s not
about making things vanish before our
eyes---at least, not yet. We can hide them
from microwaves, but the shield is plain
enough to see. This isn t like stealth
shielding on military aircraft, where
you just try to eliminate re ection---
the microwaves seem literally to pass
Artificially structured metamaterials could transform
telecommunications, data storage, and even solar
energy, says David R. Smith. By Philip Ball
Feiner, the director of Columbia Uni-
versity s Computer Graphics and User
Interfaces Laboratory, undertook some
of the earliest research in the field and
finds the Nokia project heartening. "The
big missing link when I started was a
small computer," he says. "Those small
computers are now cell phones."
Despite the availability and fairly low
cost of the sensors the Nokia team
used, some engineers believe that
they introduce too much complexity
for a commercial application. "In my
opinion, this is very exotic hardware to
provide," says Valentin Lefevre, chief
technology officer and cofounder of
Total Immersion, an augmented-reality
company in Suresnes, France. "That s
why we think picture analysis is the
solution." Relying on software alone,
Total Immersion s system begins with a
single still image of whatever object the
camera is aimed at, plus a rough digital
model of that object; image-recognition
algorithms then determine what data
should be superimposed on the image.
The company is already marketing a
mobile version of its system to cell-
phone operators in Asia and Europe
and expects the system s first applica-
tions to be in gaming and advertising.
Nokia researchers have begun work-
ing on real-time image-recognition
algorithms as well; they hope the algo-
rithms will eliminate the need for loca-
tion sensors and improve their system s
accuracy and reliability. "Methods that
don t rely on those components can be
more robust," says Kari Pulli, a research
fellow at the Nokia Research Center in
Palo Alto, CA.
All parties agree, though, that mobile
augmented reality is nearly ready for the
market. "For mobile-phone applications,
the technology is here," says Feiner. One
challenge is convincing carriers such as
Sprint or Verizon that customers would
pay for augmented-reality services. "If
some big operator in the U.S. would
launch this, it could fly today," Pulli says.
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