Physicists scale up invisibility cloaks using natural crystals

Feb 01, 2011

(PhysOrg.com) -- Physicists from the University of Birmingham, with colleagues at Imperial College, London, and Technical University of Denmark, have demonstrated an 'invisibility cloak' that can hide a three-dimensional object, centimetres in dimension, large enough for the cloaking area to be visible to the human eye, according to research published today in the journal Nature Communications.

The scientists have shown that they are able to hide an object that is much bigger than those cloaked by other research groups. Previous studies have demonstrated cloaking by using a metamaterial - a fabricated composite with not found in nature - which limits the size of the cloaking region, while the team from UK and Denmark have used a natural crystal called calcite, which has enabled them to hide a larger object.

Calcite is a transparent mineral with birefringent or double-refraction properties, which means that light enters the calcite and splits into two rays of different polarizations travelling at different speeds and in different directions.

The team has been able to cloak larger objects because it has employed a cloaking design that did not require inhomogeneous material properties, as all the previous works did. This demonstration was performed, both in the air and in a container of liquid, by using two triangular pieces of calcite glued together, placed on a mirror. The size of the cloaking area is not limited by the technology available, only by the size of the calcite crystal.

Dr Shuang Zhang, lead investigator from the University of Birmingham’s School of Physics and Astronomy, said: ‘‘This is a huge step forward as, for the first time, the cloaking area is rendered at a size that is big enough for the observer to ‘see’ the invisible object with the naked eye.

‘By using natural crystals for the first time, rather than artificial meta-materials, we have been able to scale up the size of the cloak and can hide larger objects, thousands of times bigger than the wavelength of the light.’

He continues: ‘Previous cloaks have succeeded at the micron level (much smaller than the thickness of a human hair) using a nano- or micro-fabricated artificial composite material. It is a very slow process to make these structures and they also restrict the size of the cloaking area. We believe that by using calcite, we can start to develop a cloak of significant size that will open avenues for future applications of cloaking devices.’

Explore further: Tabletop experiment could detect gravitational waves

More information: This research has been published in the journal Nature Communications in a paper titled “Macroscopic Invisibility Cloak of Visible Light”.

Provided by University of Birmingham

5 /5 (9 votes)

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jjoensuu
1 / 5 (8) Feb 01, 2011
"...which means that light enters the calcite and splits into two rays of different polarizations travelling at different speeds..."

What I thought that the speed of light was a constant? So if it is not a constant then I guess all those calculations expecting it to be a constant do not necessarily match the reality?
Bob_B
4.2 / 5 (5) Feb 01, 2011
In a vacuum, in a vacuum. Calcite is not a vacuum.
Mr_Man
3.7 / 5 (3) Feb 01, 2011
What I thought that the speed of light was a constant?


Air, glass, water, human eyes, any matter that light can pass through slows down light.
Yellowdart
1 / 5 (3) Feb 01, 2011
What I thought that the speed of light was a constant? So if it is not a constant then I guess all those calculations expecting it to be a constant do not necessarily match the reality?


The speed of light does not suggest direction, only magnitude. It is a scalar, and frankly an average value determined in a vacuum. You can not, at least currently, determine the one way or velocity of light in a vacuum.

nuge
1 / 5 (3) Feb 01, 2011
Correct me if I'm wrong, but I think you can still see the metamaterial cloak itself when they do this, just not the object inside the cloak. So despite all the excitement, these invisibility cloaks are actually fairly pointless. I guess folks are just capitalising on the popularity of Harry Potter for research funding to fuck around with metamaterials. Which is actually okay by me, but anyway..
hylozoic
2 / 5 (3) Feb 01, 2011
Great. A civilization that loves to believe its own lies may be able to hide stuff better. Just perfect.
Ramael
3 / 5 (2) Feb 01, 2011
lol hylozoic. What would you rather have for this civilization, if cloaking falls outside your arena of acceptability?
hard2grep
1 / 5 (1) Feb 02, 2011
I think they should get funding from Oscar Meyer.
TechnoPagan
5 / 5 (5) Feb 02, 2011
Correct me if I'm wrong, but I think you can still see the metamaterial cloak itself when they do this, just not the object inside the cloak. So despite all the excitement, these invisibility cloaks are actually fairly pointless. I guess folks are just capitalising on the popularity of Harry Potter for research funding to fuck around with metamaterials. Which is actually okay by me, but anyway..


History is full of this kind of silly research. The first light bulbs lasted only a few hours. What a joke! And the Wright brothers first flight only lasted 12 seconds! I mean, what's the point, right? ENIAC, one of the first real computers cost half a million dollers (in 1943) and didn't have the processing power of some scientific calculators today. I don't know why they even bother.
antialias
5 / 5 (2) Feb 02, 2011
Who cares if you can still see the metamaterial?
This stuff isn't for making Harry Potter gadgets. Use a few cm wide strip of these metamaterials to direct EM radiation (like data transmissions) around immobile objects (like mountains or buildings). Use it in highly integrated photonic circuits to route signals around non-transparents switches or amplifiers. This way can still go the shortest path without haing to use mirrors or additional amplifiers.
MarkyMark
5 / 5 (1) Feb 06, 2011
@ antialias

Exactly such technology is for more than making an 'invisabilaty' cloak. Though i admit it would be fun to go around scaring people in my skintight invisabilaty cloak, only when drunk tho ;)
Oxensraiser?
1 / 5 (1) Mar 23, 2011
This is not cloaking. This is a victorian era parlor trick done with glass and mirrors. LITERALLY.(just substitute calcite for glass). And the calcite itself isnt invisible, so you have LARGE slabs of crystal either moving around on a frame, or just set in place, and boy is that pretty frickkin' obvious. "OMG stuff becomes invisible when you hide it behind other stuff!" This is just a version of Solid Snake's box, without the helpful programed ignorance of those its supposed to fool. And as for passive security, might as well hide stuff behind a billboard that says "Hey guys, the valuables are here!"

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