Science

'Invisibility cloak' hides objects without using metamaterials

'Invisibility cloak' hides obj...
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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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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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)
The wedge measuring 38mm x 10mm x 2mm visible to the naked eye.
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The wedge measuring 38mm x 10mm x 2mm visible to the naked eye.
Part of the pink object is rendered invisbile to the naked eye under the calcite-based invisibility cloak
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Part of the pink object is rendered invisbile to the naked eye under the calcite-based invisibility cloak

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.

The wedge measuring 38mm x 10mm x 2mm visible to the naked eye.
The wedge measuring 38mm x 10mm x 2mm visible to the naked eye.

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.

15 comments
Ianspeed
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...
bobmeyerweb
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.
Harpal Sahota
Now you c-rystal it, now you don\'t! Perio....blame it on the cloak! Brill!!!
jules_c
@bobmeyerweb: 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.
Facebook User
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.
jaison Sibley
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.
benedik
@jules_c 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.
jimbo92107
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.
Kermit Hale
Seems to me magicinas have been rendering things invisible for a long time. Nothing new here.
Stuart Cleveland
@benedik 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?