Thin, Active Invisibility Cloak Demonstrated for First Time
Nov. 12, 2013 — Invisibility cloaking is no longer the stuff
of science fiction: two researchers in The Edward S. Rogers Sr. Department of
Electrical & Computer Engineering have demonstrated an effective
invisibility cloak that is thin, scalable and adaptive to different types and
sizes of objects.
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Professor George Eleftheriades and PhD student Michael
Selvanayagam have designed and tested a new approach to cloaking -- by
surrounding an object with small antennas that collectively radiate an electromagnetic
field. The radiated field cancels out any waves scattering off the cloaked
object. Their paper 'Experimental demonstration of active electromagnetic
cloaking' appears today in the journal Physical Review X.
"We've taken an electrical engineering approach, but
that's what we are excited about," says Eleftheriades. "It's very
practical."
Picture a mailbox sitting on the street. When light hits the
mailbox and bounces back into your eyes, you see the mailbox. When radio waves
hit the mailbox and bounce back to your radar detector, you detect the mailbox.
Eleftheriades and Selvanyagam's system wraps the mailbox in a layer of tiny
antennas that radiate a field away from the box, cancelling out any waves that
would bounce back. In this way, the mailbox becomes undetectable to radar
.
"We've demonstrated a different way of doing it,"
says Eleftheriades. "It's very simple: instead of surrounding what you're
trying to cloak with a thick metamaterial shell, we surround it with one layer
of tiny antennas, and this layer radiates back a field that cancels the
reflections from the object."
Their experimental demonstration effectively cloaked a metal
cylinder from radio waves using one layer of loop antennas. The system can be
scaled up to cloak larger objects using more loops, and Eleftheriades says the
loops could become printed and flat, like a blanket or skin. Currently the
antenna loops must be manually attuned to the electromagnetic frequency they
need to cancel, but in future they could function both as sensors and active
antennas, adjusting to different waves in real time, much like the technology
behind noise-cancelling headphones.
Work on developing a functional invisibility cloak began
around 2006, but early systems were necessarily large and clunky -- if you
wanted to cloak a car, for example, in practice you would have to completely
envelop the vehicle in many layers of metamaterials in order to effectively
"shield" it from electromagnetic radiation. The sheer size and
inflexibility of the approach makes it impractical for real-world uses. Earlier
attempts to make thin cloaks were not adaptive and active, and could work only
for specific small objects.
Beyond obvious applications, such as hiding military
vehicles or conducting surveillance operations, this cloaking technology could
eliminate obstacles -- for example, structures interrupting signals from
cellular base stations could be cloaked to allow signals to pass by freely. The
system can also alter the signature of a cloaked object, making it appear
bigger, smaller, or even shifting it in space. And though their tests showed
the cloaking system works with radio waves, re-tuning it to work with Terahertz
(T-rays) or light waves could use the same principle as the necessary antenna
technology matures.
"There are more applications for radio than for
light," says Eleftheriades. "It's just a matter of technology -- you
can use the same principle for light, and the corresponding antenna technology
is a very hot area of research."
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Original Story here @ ScienceDaily http://www.sciencedaily.com/releases/2013/11/131112132627.htm
