男女羞羞视频在线观看,国产精品黄色免费,麻豆91在线视频,美女被羞羞免费软件下载,国产的一级片,亚洲熟色妇,天天操夜夜摸,一区二区三区在线电影
   

Scientists create cloak of invisibility

(AP)
Updated: 2006-10-20 07:08

WASHINGTON - Scientists are boldly going where only fiction has gone before - to develop a Cloak of Invisibility. It isn't quite ready to hide a Romulan space ship from Capt. James T. Kirk or to disguise Harry Potter, but it is a significant start and could show the way to more sophisticated designs.


A photo of the "metamaterial" cloak, released to Reuters on October 19, 2006, which deflects microwave beams so they flow around a "hidden" object inside with little distortion, making it appear almost as if nothing were there at all. U.S. and British scientists said on Thursday they had found a way to hide an object from microwave radiation in a first step toward making a what they hope will be an invisibility cloak. [Reuters]
In this first successful experiment, researchers from the United States and England were able to cloak a copper cylinder.

It's like a mirage, where heat causes the bending of light rays and cloaks the road ahead behind an image of the sky.

"We have built an artificial mirage that can hide something from would-be observers in any direction," said cloak designer David Schurig, a research associate in Duke University's electrical and computer engineering department.

For their first attempt, the researchers designed a cloak that prevents microwaves from detecting objects. Like light and radar waves, microwaves usually bounce off objects, making them visible to instruments and creating a shadow that can be detected.

Cloaking used special materials to deflect radar or light or other waves around an object, like water flowing around a smooth rock in a stream. 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 new work points the way for an improved version that could hide people and objects from visible light.

Conceptually, the chance of adapting the concept to visible light is good, Schurig said in a telephone interview. But, he added, "From an engineering point of view it is very challenging."

The cloaking of a cylinder from microwaves comes just five months after Schurig and colleagues published their theory that it should be possible. Their work 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 said. 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," Smith said.

The cloak is made of metamaterials, which are mixtures of metal and circuit board materials such as ceramic, Teflon or fiber composite.

In an ideal situation, the cloak and the item it is hiding would be invisible. An observer would see whatever is beyond them, with no evidence the cloaked item exists.

"Since we do not have a perfect cloak at this point, there is some reflection and some shadow, meaning that the background would still be visible just darkened somewhat. ... We now just need to improve the performance of cloaking structures."

In a very speculative application, he added, "one could imagine 'cloaking' acoustic waves, so as to shield a region from vibration or seismic activity."

Natalia M. Litchinitser, a researcher at the University of Michigan department of electrical engineering and computer science who was not part of the research team, said the ideas raised by the work "represent a first step toward the development of functional materials for a wide spectrum of civil and military applications."

Joining Schurig and Smith in the project were researchers at Imperial College in London and SensorMetrix, a materials and technology company in San Diego.

The research was supported by the Intelligence Community Postdoctoral Research Fellowship Program and the United Kingdom Engineering and Physical Sciences Research Council.

 
 

主站蜘蛛池模板: 同仁县| 伊春市| 佛坪县| 郴州市| 龙山县| 东丰县| 桂林市| 阳春市| 德格县| 子洲县| 博客| 叙永县| 天柱县| 遂昌县| 墨玉县| 罗山县| 青河县| 永嘉县| 东台市| 大关县| 德钦县| 稷山县| 依兰县| 灯塔市| 富蕴县| 巩义市| 砚山县| 南京市| 安阳市| 洪洞县| 抚宁县| 封丘县| 固阳县| 荣成市| 筠连县| 名山县| 大同县| 正定县| 高淳县| 淮滨县| 仪征市| 措美县| 探索| 柳州市| 项城市| 二手房| 马尔康县| 香河县| 贵南县| 兴城市| 新密市| 紫云| 永定县| 桐乡市| 临漳县| 乐亭县| 二连浩特市| 平山县| 桂林市| 寻乌县| 洪泽县| 汾阳市| 广德县| 景宁| 香格里拉县| 喀喇沁旗| 信阳市| 轮台县| 长武县| 广东省| 定安县| 香格里拉县| 伊金霍洛旗| 玉山县| 雷山县| 乐亭县| 越西县| 江山市| 南和县| 伊宁市| 手游| 盐城市|