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 While the holy grail of metamaterials is still to make objects and
people invisible to the eye, they are set to have a more tangible
commercial impact playing more mundane roles — from satellite
antennas to wirelessly charging cellphones.
Metamaterials are simply materials that exhibit properties not found
in nature, such as the way they absorb or reflect light. The key is
in how they're made. By assembling the material — from photonic
crystals to wire and foam — at a scale smaller than the length of
the wave you're seeking to manipulate, the wave can, in theory, be
bent to will.
This makes metamaterials the tool of choice for scientists racing to
build all sorts of wave-cloaking devices, including the so-called
invisibility cloak — a cover to render whatever's inside effectively
invisible by bending light waves around it.
"The invisibility cloak was just one more thing we were discovering — that we have all this flexibility in this material and here's
another thing we can do," David Smith of Duke University, widely
regarded as one of the founding fathers of metamaterials, said in a
telephone interview. "But we're equally interested in seeing this
transition in making a difference in people's lives."
Indeed, Smith's own journey from laboratory to factory illustrates
that while metamaterials have for some become synonymous with "Harry
Potter" cloaks, their promise is more likely to be felt in a range
of industries and uses, from smaller communication devices to
quake-proof buildings.
BENDING LIGHT
At the heart of both metamaterials and invisibility are waves. If
electromagnetic waves — whether visible light, microwave or infrared — can be bent around an object it would not be visible on those
wavelengths. It was long thought you couldn't control light in this
way with natural materials as their optical properties depended on
the chemistry of the atoms from which they were made.
It was only when Smith and his colleagues experimented with altering
the geometry of material in the late 1990s that they found they
could change the way it interacted with light, or other kinds of
wave — creating metamaterials. With that, says Andrea Alu, an
associate professor at the University of Texas at Austin, scientists
found "it may be possible to challenge rules and limitations that
were for centuries considered written in stone."
The past decade has seen an explosion in research that has built on
Smith's findings to make objects invisible to at least some forms of
light.
"There have now been several demonstrations of cloaking at visible
wavelengths, so cloaking is truly possible and has been realized,"
says Jason Valentine of Vanderbilt University, who made one of the
first such cloaks. These, however, have limitations — such as only
working for certain wavelengths or from certain angles. But the
barriers are falling fast, says Valentine.
In the past year, for example, Duke University's Yaroslav Urzhumov
has made a plastic cloak that deflects microwave beams using a
normal 3D printer, while Alu has built an ultra-thin cloak powered
by electric current.
INVISIBLE ARMY?
Funding much of this U.S. research is the military.
Urzhumov said in an email interview that the U.S. Department of
Defense is "one of the major sponsors of metamaterials and
invisibility research in the U.S." The Defense Advanced Research
Projects Agency, which commissions advanced research for the
Department of Defense, has funded research into metamaterials since
2000, according to the department's website.
Military interest in metamaterials was primarily in making a cloak,
said Miguel Navarro-Cia of Imperial College London, who has
researched the topic with funding from the European Defence Agency
and U.S. military.
But an invisibility cloak needn't be a sinister tool of war.
Vanderbilt's Valentine suggests architectural usage. "You could use
this technology to hide supporting columns from sight, making a
space feel completely open," he said.
Other potential uses include rendering parts of an aircraft
invisible for pilots to see below the cockpit, or to rid drivers of
the blind spot in a car.
Military or not, this is all some way off.
"Most invisibility cloaks, essentially, are still in the research
stage," says Ong Chong Kim, director at the National University of
Singapore's Centre for Superconducting and Magnetic Materials.
MAKING WAVES
Ong and others say that while metamaterials may not yet be making
objects invisible to the eye, they could be used to redirect other
kinds of waves, including mechanical waves such as sound and ocean
waves. French researchers earlier this year, for example, diverted
seismic waves around specially placed holes in the ground,
reflecting the waves backward.
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Ong points to the possibility of using what has been learned in
reconfiguring the geometry of materials to divert tsunamis from
strategic buildings.
Elena Semouchkina, a pioneer on cloaking devices at Michigan
Technological University, points to screening antennas so they don't
interfere with each other, protecting people from harmful radiation
or acoustic pressure, and even preventing buildings from destruction
from seismic waves.
Metamaterials could also absorb and emit light with extremely high
efficiency — for example in a high-resolution ultrasound — or
redirect light over a very small distance. This, says Anthony Vicari
of Lux Research, "could be used to improve fiber optical
communications networks, or even for optical communications within
microchips for faster computing."
COMMERCIAL USES
Indeed, there's clearly a growing appetite for commercializing the
unique properties of metamaterials.
One of the first to do so was the new defunct Rayspan Corp, a
California-based company whose antennas found their way into WiFi
routers from networking manufacturer Netgear Inc and a superflat
smartphone from LG Electronics Inc.
The antennas were smaller, flatter and performed better than other
options, but integrating them into the rest of the phone proved
difficult, said former Rayspan executives. A spokesman for LG said
the project was no longer active and LG had no plans to apply
metamaterials in other products.
"One thing from my experience as an entrepreneur is that technology
gets very excited about what it's doing in the lab," said Maha
Achour, who co-founded Rayspan, "but the reality when you
commercialize things is completely different." The company's patents
have since been sold to an undisclosed buyer.
The lessons have been learned. Now, the focus has shifted to using
metamaterials in products in markets where they can more easily gain
a commercial foothold.
Smith, who built the first metamaterials in 1999, has led the
charge, teaming up with Intellectual Ventures, a patent portfolio
firm, to spin off two companies: Kymeta Corp, making flat-panel
antennas for satellite communications, and Evolv Technologies, which
hopes to make a lighter, faster and portable airport scanner — with
no moving parts. Kymeta, in partnership with satellite operators
Inmarsat and O3b Networks, hopes to ship in early 2015.
The two fields were chosen from a shortlist of 20 potential markets,
Smith said. "They're the same metamaterials behind the cloak, but we
were looking for more near-term applications."
WIRELESS CHARGING
The next likely consumer use of metamaterials could be in the
wireless charging of devices, an area attracting keen industry
attention.
Mark Gostock of ISIS Innovation Ltd, an Oxford University research
commercialization firm, said he was in talks with several
manufacturers to license ISIS' technology. Samsung Electronics has
filed several patents related to metamaterials and wireless
charging, but declined to comment for this article.
Other companies that cite metamaterials in their patent filings
include Harris Corp, NEC Corp, Hewlett-Packard Co and Panasonic
Corp.
Eventually, says Wil McCarthy, chief technology officer of
Denver-based smart window maker RavenBrick LLC and holder of a
patent he hopes will bring metamaterials to polarizing windows,
metamaterials will be incorporated without much fanfare.
"The people buying these products will have no idea how they work,
and won't know or care that they're doing things that were
previously considered impossible," he says.
(Editing by Ian Geoghegan)
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