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: 阿拉善盟| 镇平县| 霍邱县| 孝感市| 奉化市| 江陵县| 望谟县| 永昌县| 理塘县| 金华市| 抚远县| 延安市| 张家川| 汪清县| 上高县| 溧水县| 如东县| 肥乡县| 莱阳市| 和林格尔县| 抚顺县| 环江| 若尔盖县| 遵义市| 屏南县| 英吉沙县| 临清市| 内江市| 鞍山市| 辉县市| 深州市| 新密市| 和龙市| 德惠市| 肃宁县| 称多县| 贺兰县| 赤城县| 都江堰市| 清水河县| 青岛市| 万盛区| 梨树县| 鄂托克前旗| 手机| 阿拉尔市| 通化市| 涞源县| 织金县| 美姑县| 大英县| 新民市| 专栏| 宝丰县| 英超| 文成县| 墨竹工卡县| 绥宁县| 武夷山市| 海原县| 二连浩特市| 舟曲县| 佛教| 伊宁市| 丰顺县| 永登县| 都匀市| 琼海市| 安化县| 沁阳市| 潍坊市| 台湾省| 永泰县| 都兰县| 双城市| 临朐县| 张家界市| 锡林郭勒盟| 云和县| 浠水县| 荆州市| 广平县|