Which one would you like to have - an invisible sphere or an invisibility cloak?
These are actually two entirely different devices according to scientists.
For a long time the idea that objects or persons could become invisible was considered pure science fiction.
This has changed in the recent years, as invisibility
technology is quickly becoming reality, or at least that is what scientists hope when developing and testing advanced cloaking prototypes.
In a paper published in Science in 2006,
John Pendry of Imperial College London and David Schurig and David Smith of Duke University wrote
that "a cloak of invisibility is in principle possible, at least over a narrow frequency band" and presented the first practical realization of such a cloak.
Their "cloaking" prototype was impressive but still not perfect as probably expected.
Refining the cloaking technology continues all the time.
The Duke University team has extensive experience in creating "meta-materials," man-made objects that have properties often absent in natural ones.
Structures incorporating meta-materials can be designed to guide electromagnetic waves around an object, only to have them emerge on the other side as if
they had passed through an empty volume of space, thereby cloaking the object.
"In order to create the first cloaks, many approximations had to be made in order to fabricate the intricate meta-materials used in the device,"
said Nathan Landy, a graduate student working in the laboratory of senior
investigator David R. Smith, William Bevan Professor of electrical and computer engineering at Duke's Pratt School of Engineering.
"One issue, which we were fully aware of, was loss of the waves due to reflections at the boundaries of the device," Landy said. He explained that it was much
like reflections seen on clear glass. The viewer can see through the glass just fine, but at the same time the viewer is aware the glass is present due to light
reflected from the surface of the glass.
Landy and his team have successfully constructed a working prototype.
"It split light into two waves which traveled around an object in the center and re-emerged as the single wave
with minimal loss due to reflections."
Landy presents the cloak.
Landy said this approach could have more applications than just cloaks. For example, meta-materials can "smooth out" twists and turns in fiber optics,
in essence making them seem straighter. This is important, Landy said, because each bend attenuates the wave within it.
The researchers are now working to apply the principles learned in the latest experiments to three dimensions, a much greater challenge than in a
In 2011, Janos Perczel, a 22-year old undergraduate at the University of St Andrews in Scotland published a paper describing an
'invisible sphere' that slowed down light, potentially allowing the device to remain invisible in front of ever-changing backgrounds of different colors.
This makes us wonder - what are the differences between an invisible sphere and an invisibility cloak?
In an interview with the Voice of Russia,
Janos Perczel explained that people should not confuse these two devices. "There are substantial differences between our sphere and what you see in the
Harry Potter movies.
Most important of them being that the invisibility cloak in Rowling's novel is moldable, while our optical device is a rigid sphere-like object.
You cannot change its shape or wrap it around yourself. The flexibility of the cloak that you so often see in the movies is incredibly difficult to
achieve in reality.
Admittedly, there are certain proposals how to do this, especially from St Andrews.
Dr Andrea Di Falco has recently come up with the idea of flexible meta-materials which might eventually lead to the creation of Harry-Potter-like cloaks.
For now, however, rigid box or sphere-like invisibility
devices seem to be more realistic and, indeed, are already being produced in experimental science labs," Perczel said
Perczel hopes that if an invisible sphere will be used in reality it will be done to achieve something good.
"The decision about how the device will be used in
practice usually belongs to the engineers, designers, and production managers who know the market well and can foresee what will sell better.
Imagine all you could do if you were invisible…
Obviously, our device can be used to make things invisible when needed. I am worried about the potential military use of our optical sphere, especially in the
area of the development of new invisible weapons.
My hope is that the invisible sphere would be used in more peaceful ways. One of them might be shielding people from hazardous forms of radiation.
Still, these are just suggestions."
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