Tip:
Highlight text to annotate it
X
[flourish]
>> NARRATOR: Cloaking. It's one of the coolest technologies to come out of Star Trek, right
alongside fazers and transporters. But is it science fiction, or just plain science?
Is it actually possible to make something look like it's disappeared? Dr. Andrea Alu
of the University of Texas at Austin thinks so. With funding from the National Science
Foundation and the Department of Defense, he and his research group are working on new
ways of cloaking objects in their lab ... and have had some impressive results.
>> ANDREA ALU: Cloaking is an attempt to reduce the visibility of an object. So if we're
trying to reduce the visibility to humans, then what we would try to do is to suppress
all the light waves that get scattered -- or get bounced off -- the surface of an object
in all directions and for all observers.
>> JASON SORIC: There's a lot of people worldwide that are working on cloaking right
now. It's a very hot topic, it's very exciting right now. And they all have different
approaches. But this one's very unique.
>> NARRATOR: We see things in the visible spectrum, a very narrow portion of the electromagnetic
spectrum composed of the different wavelengths that constitute color. Light waves bounce
- or scatter - off of an object and return to our eyes., which are effectively sensors
that detect color, shape, and other features based on what scatters back to them.
>> SORIC: When something scatters, what we look for is how the field is perturbed around
the object. So if nothing's there, we actually see kind of a plain wave going by in time.
And when you put the object there without a cloak, just the object by itself, what ends
up happening is that it bends ... it bends the wave around it a little bit, and it also
scatters it in different places. So it'll create, like, shadows behind it and stuff.
>> NARRATOR: Current stealth devices make an object less detectable by absorbing the
incoming wave or re-directing it away from the observer. If no scattered wave is picked
up, the object cannot be detected. However, stealth may be tricked by moving the observer
or by detecting the shadow of the object. The cloaking approach works by placing something
around the object that cancels the wave for all observers, even on the shadow side.
>> SORIC: A lot of people I've seen have related it to like a rock in the water. You
can actually see the water bending around the object. But if you were to put a cloak
around that rock, it would literally just go right through it. It's as if it wasn't
even there.
>> NARRATOR: Alu and his group have successfully done this, cloaking a cylinder to sensors
that observe microwaves. They utilize the longer wavelength of this spectrum because
it's easier to demonstrate proof of cloaking, and it's more cost-effective. If our eyes
saw microwaves instead of visible light, this cylinder would be invisible. The cylinder
is 18 centimeters long, a little under two wavelengths. To conduct the same experiment
in the visible spectrum, the cylinder would have to be around 1 micrometer long, or 100,000
times smaller. For scientific purposes, utilizing the microwave spectrum is much more practical.
>> ALU: It started really as a theoretical type of work in which people were trying to
show that by using some special materials around an object, it's possible to isolate
that object completely from the background and avoid any type of bouncing of waves. So
that would make not only the object less reflecting, but also completely transparent, so even if
an observer was placed on the back of the obstacle, it would see the source of the electromagnetic
wave as if there was nothing in between. So it suppresses also the shadow of an object.
>> NARRATOR: The "special materials" Alu refers to are known as metamaterials. Metamaterials
are manufactured to meet exact specifications using nanoscale technology, and can be made
to exhibit exotic properties that don't occur naturally.
>> ALU: Since about ten years, the field of nanotechnology has exploded, and there's
a lot of interest in trying to manipulate the material properties by changing the fabrication
of these materials at the nanoscale, at the atomic scale, or the microscopic scale in
different ways. So in general, that's what we do in my group. We try to see how to apply
these metamaterials, or these artificial materials with exotic properties, to a lot of different
problems.
>> NARRATOR: The concept is straightforward. A test cylinder made of homogeneous, non-conductive
material, is placed in a container made of metamaterial specifically designed to fit
around it. This is placed in front of a horn that illuminates the unit with microwaves.
A robotic arm measures the scattered waves, and compares it to measurements taken without
the cloak. The metamaterial cloak is manufactured so that its scattering signature - the way
it scatters waves - is the exact opposite of the cylinder inside.
>> ALU: The technique works using what we call a scattering cancellation phenomenon.
So when the two are combined together, the total effect is ... what is called the destructive
interference. So the visibility of the object is completely cancelled; is zero. It's kind
of a compensation between what the object would do, and what the metamaterial would
do. When you combine the two, you cancel the scattering.
>> NARRATOR: Though conceptually straightforward, planning for this experiment is anything but
easy. The nature of the work demands a lot of computation, so Alu and his team have used
the powerful resources at the Texas Advanced Computing Center to facilitate the design
and execution of their experiments.
>> ALU: Before we can even attempt an experiment, it's always good to have a tool that can
kind of back us up and can tell us what the challenges might be. So in this sense, having
supercomputing resources within our campus is great.
>> SORIC: With just a regular desktop or something, one could wait for a week or longer, so it
helps us out a lot, actually.
>> NARRATOR: The possibility of cloaking no longer seems to be science fiction. It's
happening right now in a basement lab at the University of Texas at Austin. There are,
of course, limitations. We're not cloaking starships at this point. But one day soon,
perhaps we'll have the ability to cloak larger objects, or objects that aren't homogeneous.
And there are practical applications right around the corner, like near-field microscopy.
>> ALU: Right now, the most practical way of seeing small details of an object is to
go very close to this object because in that way, you don't need a lens. You just pick
up the fields very, very close to the object and then you can see whatever detail you like.
The problem with doing that is that you have a lot of back reflection from the tip of your
microscope. So in this sense, the cloak that we propose can be a great tool to on one hand
allow you to go very close to the object to be sensed, but on the other hand avoid any
back reflection or any scattering that can affect the measurement itself.
>> SORIC: There's a whole multitude of real practical applications for this. But then
there's also the cool part where you could, you know, make things stealthy .