Scientists closer to invisibility cloak

scourge99 · 08-14-08, 11:07 AM

Quote:

WASHINGTON - Scientists say they are a step closer to developing materials that could render people and objects invisible.

Researchers have demonstrated for the first time they were able to cloak three-dimensional objects using artificially engineered materials that redirect light around the objects. Previously, they only have been able to cloak very thin two-dimensional objects.

The findings, by scientists at the University of California, Berkeley, led by Xiang Zhang, are to be released later this week in the journals Nature and Science.

The new work moves scientists a step closer to hiding people and objects from visible light, which could have broad applications, including military ones.

People can see objects because they scatter the light that strikes them, reflecting some of it back to the eye. Cloaking uses materials, known as metamaterials, to deflect radar, light or other waves around an object, like water flowing around a smooth rock in a stream.

Metamaterials are mixtures of metal and circuit board materials such as ceramic, Teflon or fiber composite. They are designed to bend visible light in a way that ordinary materials don't. Scientists are trying to use them to bend light around objects so they don't create reflections or shadows.

It differs from stealth technology, which does not make an aircraft invisible but reduces the cross-section available to radar, making it hard to track.

The research was funded in part by the U.S. Army Research Office and the National Science Foundation's Nano-Scale Science and Engineering Center.

Sweet. I want one.

jamesrage · 08-14-08, 03:22 PM

Is this really a technology that should exist? A terrorist can hide a bomb,a enemy can fly a jet and drop a bomb on us,criminals can use this rob banks with and other criminal activities and other countries can use this to spy more easily on us.

scourge99 · 08-14-08, 03:49 PM

Quote:

Originally Posted by jamesrage

Is this really a technology that should exist? A terrorist can hide a bomb,a enemy can fly a jet and drop a bomb on us,criminals can use this rob banks with and other criminal activities and other countries can use this to spy more easily on us.

Look at the history and results of countries who have isolated themselves. They all become conquored by outsiders. Failing to stay on the cutting edge of technology results in the same. We must constantly evolve to counter new threats and create advantages of our own. Compete or become a helpless victim: what do you choose?

Kernel Sanders · 08-14-08, 06:41 PM

The "invisibility" claim is severly misleading

Full article is at [ Ars Technica | New meta-material doesn't actually render anything invisible]

Quote:

Over the past few years, there has been a lot of theoretical and experimental work on a class of structures called meta-materials. A meta-material is used to get around the limitations of natural materials by structuring them in special ways. This can best be described using quartz as an example. A single quartz crystal is pretty much transparent to visible light; a few percent of the light is reflected from the crystal surface, but otherwise it all goes through. However, if the wavelength is much shorter (on the order of the spacing between molecules), then the crystal is still transparent, but light is scattered into a pattern. Similarly, if we take a handful of quartz crystals, all the little reflections from the many surfaces scatter even visible light in every direction, resulting in white sand that is no longer possible to see through. If the quartz crystals were all the same size and shape and arranged in an orderly fashion, however, it would be possible to use them to guide visible light down specific paths as well.

Quartz demonstrates how order and scale matter in how light propagates through a material. Meta-materials take advantage of this by deliberately engineering materials to have order on scales comparable to the wavelength of light that they want to influence. This can be done by alternating layers of materials (as in antireflection coatings), by crafting arrays of holes in an otherwise solid material, or by building crystal-like structures composed of small spheres.

In certain circumstances, a meta-material can exhibit a negative refractive index (in nature, the refractive index is always positive), which causes light to bend in unexpected directions. This has proven to be difficult to achieve at visible wavelengths due to a number of challenges. A negative refractive index has to have the appropriate scale (~30nm features), which is difficult, but not impossible.

However, the electric field phase of the light also needs to be controlled. To do that, the material must respond to the light's electric field with a large opposing field that can slows the light's advance. In effect, this requires metallic structures that allow the electrons to resonate with the light field, allowing a large opposing field to build up. Making a single layer of these structures has been done before, but it's really hard to define the bulk properties of a meta-material when it's only a single layer thick.

That is what makes the new research so important. For the first time, researchers have managed to make a negative index meta-material* that is more than a single layer thick. This allowed them to directly measure its bulk properties and confirm some of the predictions for these materials. [...]

The meta-material used in this demonstration had 21 layers (ten of magnesium fluoride and 11 of silver) with 484 holes drilled through it. The holes are about 500nm in diameter, and the whole structure has a face of just 5 micrometers on a side. One face was angled so that the material acted like a prism. The researchers' measurements showed that the prism did indeed have a negative refractive index over about one-third of the near-infrared spectrum (1.45 to 1.8 micrometers, to be precise). [...]

So, if this isn't a material for making you invisible what is it good for? It's the basic material we need for beating the diffraction limit. Negative index materials are not subject to the diffraction limit, meaning that light can be focused to smaller volumes. This implies that we would be able to illuminate cellular machinery at the level of individual molecules or perhaps even individual atoms. It would even be possible to use direct chemical imaging, instead of relying on fluorescent labels. This one application, which may well be attainable with the technology the authors used in their demonstration, should be enough for anyone to get excited about.

DarkWizard12 · 08-14-08, 06:44 PM

YouTube - Scatman John - The Invisible Man