November 12, 2012
Researcher Improving On Invisibility Cloak Concepts
Michael Harper for redOrbit.com — Your Universe Online
The idea of an invisibility cloak is an attractive one to the human psyche. The ability to be present when we´re thought to be absent is a juicy prospect. Not only could we finally find out what people say about us behind our backs, but we´d also be able to watch people without being detected, as well as play some of the world´s greatest pranks.
The first notion of an achievable invisibility “cloak” arose in 2006 when researchers from Duke University and Imperial College London published a paper wherein they explained the theory of “transformation optics.” A year later, the team was able to prove their theories using a microwave. The problem here, however, is that microwaves are far too long for the human eye to see, so while the theory was proven, it did not result in what we think of as an invisibility cloak.
The key lies in a man-made material called “meta-material,” or objects which react to light in ways not found in natural objects. Objects built with (or covered in) these meta-materials can guide electromagnetic waves around the object and end up on the other side. The result is the illusion of invisibility, with the viewer seeing only what is behind the object. Nathan Landy and David Smith of Duke University have been reworking these meta-materials to make the corners and edges line up rather than cast a reflection. This sort of reflection provides an outline around the object, making it less than invisible.
“In order to create the first cloaks, many approximations had to be made in order to fabricate the intricate meta-materials used in the device,” explained Landy, a graduate student at the Pratt School of Engineering, in a prepared statement.
“One issue, which we were fully aware of, was loss of the waves due to reflections at the boundaries of the device,” said Landy, comparing this issue to the reflections seen on a clear glass. While we can see through glass, reflections still make the glass visible at the same time.
The Duke team used intersecting parallel strips of copper-imbued fiberglass to construct the first cloak nearly 5 years ago.
The new cloak builds on this design, adding copper strips to create a better-performing material. These strips create a diamond shape with an empty center. When any wave, such as light, strikes this device, the wave is either absorbed, reflected, or both. The earlier cloaking experiment only absorbed some of the waves, but not enough to negatively affect the way the cloak functioned.
These cloaks were separated into 4 quadrants. The aforementioned reflections occurred near the outer edges of these quadrants, said Landy.
“Each quadrant of the cloak tended to have voids, or blind spots, at their intersections and corners with each other. After many calculations, we thought we could correct this situation by shifting each strip so that it met its mirror image at each interface,” explained Landy.
The new version of the cloak worked, splitting the light into two waves and guiding them around the object with very little refection.
"The cloak we demonstrated in 2006 as a kind of microwave device would be very poor, but this one gets us to something that could be potentially useful," said Professor Smith, speaking with the BBC.
While the idea of an invisibility cloak is a tempting one, Landy said a more practical use of these meta materials is to improve fiber optics. With these materials in place, the light which travels these wires can flow more freely, acting as if it were flowing straight through rather than bending, bouncing and twisting along its way.