http://news.yam.com/afp/life/200808/20080811067188.html
隱形術大改良 三度空間物體也可憑空消失
法新社╱張仲琬 2008-08-11 09:20
(法新社華盛頓十日電)科學家表示,他們已創造出讓三度物體消失的物質,隱形技術又躍進一步。
這是研究人員首度以人造材料,將照射物體的光線轉向,讓三度空間物體消失。隱形技術先前僅限於極薄的二度空間物體。
研究由美國加州大學柏克萊分校科學家張翔主持,研究發現將刊登在本周出版的雜誌「自然與科學」。
這項創新成就改良隱形技術,讓人或物在光線下消失。研究成果有廣泛的應用範圍,其中包括軍事用途。
人類可以看到物體,是因為光線照射在物體上,然後反射入人眼所致。科學家利用名為「超材料」的物質,造成物體周圍的雷達、光線或其他形式的波體偏折,原理就像溪流繞石流動一般。
http://news.yahoo.com/s/afp/20080810/sc_afp/sciencephysicsinvisibility_080810223709
Invisibility cloak now within sight: scientists
Sun Aug 10, 6:37 PM ET
PARIS (AFP) - The age-old fantasy of rendering objects invisible took a sharp step toward reality Sunday when scientists said they had created a material that can bend visible light in three dimensions.
For now the vanishing act takes place on a nanoscale, measured in billionths of a metre.
But there is no fundamental reason why the same principles cannot be scaled up one day to make invisibility cloaks big enough to hide a person, a tank or even a tanker, the scientists say.
The groundbreaking experiments, led by Xiang Zhang at the University of California at Berkeley and the Lawrence Berkeley National Laboratory, were reported simultaneously in the British journal Nature and the US-based journal Science.
Recent advances have created other so-called metamaterials, artificially engineered structures with optical properties that bend light in unnatural ways.
But previous attempts had two severe limitations.
One was that they only worked on the microwave range of the light spectrum, bending wavelengths much too long to be visible to the human eye.
The second was that -- up to now -- it only worked on thin, two-dimensional systems.
The new material, by contrast, produces what is known as the "negative refractive index" needed to make an invisibility cloak within a visible light spectrum and in three dimensions.
Negative refraction -- or "left-handed" -- materials deflect light in a way which is contrary to the normal "right-handed" rules of electromagnetism.
The light travels in the opposite direction that it normally would when passing from one material to another, such as from air through water or glass.
One possible application would be the construction of special lenses for optical microscopes that could focus on things as tiny as molecules.
But the holy grail of metamaterials has become the kind of invisibility shield that has fire the human imagination from H.G. Wells' "Invisible Man" to the adventures of Harry Potter.
The military, which funded the research, is especially keen to develop materials that could usher in an entire new generation of stealth technology.
The metamaterial developed by Zhang and his colleagues has a multi-layered fishnet structure composed of alternating layers of silver and magnesium fluoride, which is transparent over an extremely wide range of light wavelengths.
"In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object like a river flowing around a rock," Zhang said, according to the Sunday Times.
"An observer looking at the cloaked object would then see light from behind it, making it seem to disappear."