Oct. 19, 2006 — A team of American and British researchers has made a Cloak of Invisibility. Well, OK, it's not perfect. But it's a start, and it did a pretty good job of hiding a copper cylinder.
In this experiment the scientists used microwaves to try and detect the cylinder. Like light and radar waves, microwaves bounce off objects, making them visible and creating a shadow, though it has to be detected with instruments.
If you can hide something from microwaves, you can hide it from radar — a possibility that will fascinate the military.
Cloaking differs from stealth technology, which doesn't make an aircraft invisible but reduces the cross-section available to radar, making it hard to track. Cloaking simply passes the radar or other waves around the object as if it weren't there, like water flowing around a smooth rock in a stream.
The new work points the way for an improved version that could hide people and objects from visible light.
The chance of adapting the concept to visible light is good, cloak designer David Schurig said in a telephone interview.
But Schurig, a research associate in Duke University's electrical and computer engineering department, added, "From an engineering point of view it is very challenging."
Nonetheless, the cloaking of a cylinder from microwaves comes just five months after Schurig and colleagues published their theory that it should be possible.
Their first success is reported in a paper in Friday's issue of the journal Science.
"We did this work very quickly ... and that led to a cloak that is not optimal," said co-author David R. Smith, also of Duke. "We know how to make a much better one."
The first working cloak was in only two dimensions and did cast a small shadow, Smith acknowledged. The next step is to go for three dimensions and to eliminate any shadow.
Viewers can see things because objects scatter the light that strikes them, reflecting some of it back to the eye.
"The cloak reduces both an object's reflection and its shadow, either of which would enable its detection," said Smith.
In effect, the device, made of metamaterials — engineered mixtures of metal and circuit board materials, which could include ceramic, Teflon or fiber composite materials — channels the microwaves around the object being hidden.
When water flows around a rock, Smith explained, the water recombines after it passes the rock and people looking at the water downstream would never know it had passed a rock.
The cloaking has to be designed for specific bandwidths of radiation.
In this case it's microwaves, and someone measuring them wouldn't be able to tell they had passed around an object. The hope is to do the same for light waves.
