加拿大研究人员开发雷达“隐身衣”

 　　加拿大研究人员开发雷达“隐身衣”

　　TORONTO, Nov. 25 (Xinhua) --- Witches and magic may not exist, but Harry 1 Potter's invisibility cloak certainly does.
　　A pair of researchers in the Canadian city of Toronto have developed their very own cloaking method that could pretty much make any object disappear not to the human eye yet but on radar 2.
　　Since 2006, researchers from around the world have been working to create a functioning invisibility cloak using metamaterials artificial materials engineered to steer 3 light to hide objects which could be impractical 4 since the material often had to be as thick and large as the object it was being used to hide.
　　But University of Toronto electrical and computer engineering professor, George Eleftheriades, and Ph.D. candidate Michael Selvanayagam's innovation, published in the latest journal Physical Review X, offer a much different approach.
　　"We were looking at a way to develop a cloaking mechanism 5 that was different from previous works where they use materials and bend light around the objects, we were trying to use sources to bend light around an object," Selvanayagam explained to Xinhua.
　　The idea is simple, said Eleftheriades. Instead of cloaking with a physical material, they surround the object with antennae 6 which radiate an electromagnetic field, making it virtually undetectable to microwave and radio wave detectors 7.
　　"Waves do not bounce around, the light that normally reflects from an object now is cancelled, so if you cancel the reflections, there is no shadow, there are no reflections coming out of the object and so it becomes invisible," he said.
　　To demonstrate their idea, the pair created an apparatus 8 a contained metal box roughly the size of a pool table. Set in the center of the box is a metal cylinder 9, which has 12 antennae surrounding it.
　　Each antennae fires waves back to nullify the waves, according to Selvanayam. Likening the metal box to a water tank, the incoming waves, instead of scattering 10 as it hits the object, will then pass through completely unaffected as if the object did not exist.
　　"The wavefronts stay circular now as they travel through because the cloak suppresses the light that scatters 11 off the object," said Selvanayagam as he explained the shots taken of the waves before and after the demonstration 12. "And so we can see that the cloaking effect in terms of these wavefronts look like they're just travelling right through."
　　Besides offering up a cool technology, the duo said their work could also have some very practical real-world applications. Other than military use, it could also be used to create extremely thin lenses and devices that wouldn't otherwise be possible. Cell phone signals could also be enhanced by making buildings obstructing 13 cell phone radiation "disappear."
　　And a Harry Potter like invisibility cloak that can camouflage 14 objects to the naked eye may also become a very real possibility in the near future as technology continues to develop, according to the pair.
　　"If you have a way to make nano-antennas 15 that replace these antennas for radio waves and control what light they radiate, this can become also something that works with the eyes (to make it) invisible," said Eleftheriades. "So it's very scalable, this technology."
　　But the work isn't done yet. The Toronto duo are hoping to continue perfecting the technology. As of now, one of the biggest limitations is that they have to know where the source that's illuminating 16 the object is placed in space since they have to manually take a measurement at each point to reconstruct the image. The next step, Selvanayagam said, is to make the technology fully 17 adaptive so it can respond and adjust in real-time.
　　"Future work with this idea is to make this cloak adaptable 18 so that electronics that feed the cloak and make the cloak work could respond with the incident wave and then adapt with the change of settings so they could cancel out no matter where the object, no matter where the source is," he said.
　　Despite the long road ahead, the duo couldn't be happier with the results they've achieved over the last year-and-a-half.
　　"With any research project you want it to be something that hasn't been done before, so what people haven't thought of," said Selvanayagam. "What we were able to show you is that we were the first people to show you that active cloaking is possible."
　　"You can't really ask for more," he said.