'Invisibility cloak' hides objects without using metamaterials


February 3, 2011

Part of the pink object is rendered invisbile to the naked eye under the calcite-based invisibility cloak (Image: Baile Zhang and G. Barbastathis/SMART Centre)

Part of the pink object is rendered invisbile to the naked eye under the calcite-based invisibility cloak (Image: Baile Zhang and G. Barbastathis/SMART Centre)

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The quest to build a working “invisibility cloak” generally focuses on the use of metamaterials – artificially engineered materials with a negative refractive index that have already been used to render microscopic objects invisible in specific wavelengths of light. Now, using naturally occurring crystals rather than metamaterials, two research teams working independently have demonstrated technology that can cloak larger objects in the broad range of wavelengths visible to the human eye.

Both teams, one from the Singapore-MIT Alliance for Research and Technology (SMART Centre) and the other comprised of researchers from the University of Birmingham, Imperial College, London and Technical University of Denmark, made the breakthrough using a natural crystal called calcite.

This transparent mineral boasts an optical property known as birefringence, or double-refraction. This means that when light enters the calcite, it splits into two rays of different polarizations traveling at different speeds and in different directions. This causes objects viewed through a clear piece of calcite to appear doubled.

To create their invisibility cloak, the University of Birmingham team glued two pieces of calcite with differing optical paths together and placed them on a mirror and performed demonstrations in both air and a container of liquid.

Meanwhile, the SMART Centre team used a similar method. They glued together two pieces of calcite to form a small wedge measuring 38mm x 10mm x 2mm and is placed over an intended object. Due to the light bending as it enters the cloak, objects are rendered invisible when the viewer looks from the left and right sides of the wedge, meaning it remains visible when viewed from other angles.

Although currently the cloaks can hide only small objects, such as a pin or paperclip, the technology is limited only by the size of the calcite crystal.

‘‘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,” said Dr Shuang Zhang, lead investigator from the University of Birmingham’s School of Physics and Astronomy. “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.”

Additionally, the calcite-based cloaks are much cheaper to create than those using metamaterials. The cloak developed by the SMART Centre team costs less than $US1,000, which is extraordinarily cheap by research standards.

The SMART Centre team’s research was published in Physical Review Letters on January 18, while the University of Birmingham team’s research was published in the journal Nature Communications on February 1.

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag. All articles by Darren Quick

I invented an invisibility cloak ten years ago. Unfortunately I put the plans in the pocket of the cloak, been looking for it ever since I put it down somewhere...


Based on the photo, it seems that while the object is hidden, the \"cloak\" itself is visible. That would seem to limit the practical uses a bit, don\'t you think? It\'s an interesting exercise, but I don\'t think teenage boys will be using it to sneak into the girls restroom anytime soon.


Now you c-rystal it, now you don\'t!

Perio....blame it on the cloak!


Harpal Sahota


That is a remarkably shortsighted comment. The military potential of this technology, even in its current form, is simply overwhelming. Imagine a platoon of units closing in on your location, but you can only tell that \"something\" is approaching - you can\'t even know whether it\'s infantry or armour! This is the sort of thing that can decide world wars, nothing short of the atomic bomb.


Gizmag gets a blue ribbon for having the first popular article about this kind of tech in the last decade that doesn\'t mention Harry Potter.

Facebook User

It will be intersting to see the next step : Embedding Calcite nano crystals in a metamaterial cloak ... Calcite will block things sideways and metamaterial the rest or multiple layers of nano-calcites reducing the size of the seen object to minimal some mild metamaterial input ....Intersting.

jaison Sibley


That is a remarkably silly comment. A giant wall made of cardboard could do exactly that in a military situation, and doesn\'t break when it gets shot. I am fairly sure that cardboard does not have the same destructive power as an atomic bomb, nor will it win any battles. This trite idea of military use is currently much too complicated, even from a geometric standpoint.


This article screams for a video clip. That would make it much clearer what\'s supposed to be invisible and what\'s not. It\'s hard to show what\'s hidden AFTER you hid it, unless you show what it looked like BEFORE you hide it.


Seems to me magicinas have been rendering things invisible for a long time. Nothing new here.

Kermit Hale


While non sequiturs are a great deal of fun to imagine up, they are useless if you\'re trying to make a point. A giant wall of cardboard? This has nothing to do with an invisibility cloak. Your conclusion does not follow. Also, it is incredibly naive of you to say that invisibility will not win any battles. The art of being hidden, believe it or not, is an enormous tool that is decisive in battles, one example being the sniper. jules_c does have a point. Take the destructive power and psychological power that one sniper can create, multiply it, and you have a fantastic advantage. As to your claim that using this technology is too complicated, I reply with a question-when has a revolutionary advancement in science ever been EASY to use when it was first developed?

Stuart Cleveland

@R Stuart Cleveland Funny

You need to follow the argument not skim read, jules_c makes it explicit that we are talking about it in its current for - all your talk of snipers is what, a straw man. In its current form it is WORSE then current technology all it does is hide what is there behind a giant wall of crystal????

Better off using a bedsheet - cheaper, mobile!!!, proven technology and doesnt scream \"bomb me, I\'m super expensive, unique and valuable\"

Or make things invisable the with current tech, its called camo - makes things behind it invisible by putting something in front of it


So many intelligent people makes me feel kind of out of my depth, however I will give it a go.

You cannot see through card board so anything behind it is not visible however that does not make it invisible just obstructed.

The Ninjas in Japan exploited the blind spots in the eye so as to disappear much smarter and you don\'t have to glue anything.

As for the gentleman who lost his coat, I have found it and I am happy to give it back if he can prove it is his. I will need a description.

Nick Rowney

@benedik - February 6, 2011 @ 03:16 pm PST

Damn, I was thinking \"Yes, you can use it right now. That\'ll work.\" Then I got to your post and laughed my arse off.

Okay, yup. Props to you. As it currently stands, a large piece of cardboard would do exactly the same thing!!!



Am I the only one that thinks that an invisibility cloak would be 1,000 times as valuable to a terrorist than it would be to us? Terrorists rely on stealth, while we generally use brute force. Just think of damage that Al-Quida could do with one of these if they captured one, not to mention the fact that all the research info is being published on sites like this.

David Leithauser

I am not impressed.

I got a much simpler and implementable idea years ago - I have no connections for building a prototype but it should render automobile sight better by eliminating the obtruding effect of windshield struts -for example. Some day my idea will be found by somebody else - I am sure :) , if nobody contacts me first. Best regards.

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