Nearly perfect, ultrathin invisibility cloak could have wide practical applications

January 17, 2013 by Lisa Zyga, feature

The dc invisibility cloak has a thickness of just one unit cell and can cloak an object nearly perfectly. The inset shows an enlarged view of the cloak’s resistor network. Credit: Wei Xiang Jiang, et al. ©2013 American Institute of Physics
(—Researchers have created a dc invisibility cloak made of a metamaterial that not only shields an object almost perfectly, but at 1-cm thick is also the thinnest cloak ever constructed, reaching the ultimate limit of thinness for artificial materials. As the first invisibility cloak that combines both near-perfect performance and extreme thinness, it could open the doors to practical applications. In the past, invisibility cloaks have been too large to be used in many real-world applications.

The researchers, led by Tie Jun Cui at Southeast University in Nanjing, China, have published their paper on the ultrathin but nearly perfect in a recent issue of Applied Physics Letters.

The key to making a material that can prevent another object from being seen—or from being detected by electromagnetic waves in any way—is to control two material parameters: electric permittivity and magnetic permeability. Electric permittivity corresponds to the degree to which a material permits the formation of an electric field within itself, while magnetic permeability corresponds to the degree to which a material can be permeated by a .

As the researchers explain, a perfect invisibility cloak must have a and permeability that are both strongly anisotropic (directionally dependent) and inhomogeneous (made of different materials). A metamaterial with these parameters is currently beyond the reach of current technology. However, by loosening these strict requirements, researchers have been able to fabricate metamaterials that mimic these properties and can be used as imperfect invisibility cloaks.

During the past several years, researchers have fabricated different kinds of invisibility cloaks using the loosened requirements. One kind is a free-space cloak, which guides incoming electromagnetic waves to propagate around the enclosed objects and continue along their original paths without interacting with the objects. Mathematically speaking, this is the equivalent of compressing the objects into a point. A second cloak, called a ground-plane or carpet cloak, can hide objects on the ground by making incoming electromagnetic waves appear to be reflected by a flat plane instead of the objects. This time, the objects are mathematically compressed into a two-dimensional sheet instead of a point. Both of these two types of cloaks hide objects imperfectly, and they also both take up large amounts of space due to being inhomogeneous, which limits their applications.

More recently, researchers have turned their attention to dc cloaks, which are used to hide static electric and magnetic fields. In 2012, some of the authors of the current study fabricated a dc cloak using a resistor network. This design could mimic the anisotropic property so well that the cloak had a nearly perfect cloaking performance. However, the cloak was still very large due to the material being inhomogeneous.

"If a device is inhomogeneous, that is, the device is composed of different-property materials, then such a device will be fabricated by multi-layer materials to reach the inhomogeneity," Cui told "If a device is homogeneous, however, it is possible to be fabricated by only one single cell. For , one single cell is the thinnest."

Simulation results of a metallic disk (blue circle) being cloaked by a dc invisibility cloak (thin blue circle surrounding the metallic disk). The color scale represents electric potentials and the thin black lines represent equipotential lines. Outside the cloak, the equipotential lines are almost concentric circles, showing nearly perfect cloaking effects. Credit: Wei Xiang Jiang, et al. ©2013 American Institute of Physics

Now, the researchers have demonstrated that it's possible to make a dc invisibility cloak that is made of a homogeneous and anistropic material, resulting in an ultrathin and nearly perfect cloak. They found that they could use a homogeneous material for this cloak, even though inhomogeneous materials were required for the other cloak types, by using a special optical transformation. They explained that, for a dc cloak, the transformation optics equations that are typically used to control the path of are simplified to transformation electrostatics equations. This simplification means that the metamaterial compresses the hidden object into a short line segment instead of a point.

Using transformation electrostatics, the researchers designed and fabricated a dc line-transformed invisibility cloak for the first time. The cloak is elliptical, but has such a small focal length that it is nearly circular. As a result, the cloak compresses the hidden object into such a short line segment that it is nearly a point, and therefore enables nearly perfect cloaking.

Equally as important as its performance, the cloak's thickness of a single unit cell makes it the thinnest invisibility cloak constructed to date. The researchers used a network of resistors as the metamaterial, and showed that a nearly perfect invisibility cloak could be made with just a single unit cell, which is the ultimate limit for . They explained that this extreme thinness is possible due to the metamaterial being homogeneous.

The researchers hope that this invisibility cloak could make it possible to realize a variety of applications, such as electric impedance tomography (EIT), a medical imaging technique that can detect cancer. Another application could be cloaking or detecting land mines.

"Electrostatics has wide potential applications in EIT technology, graphene, natural resource exploration, and underground archaeology," Cui said. "In our paper, we designed and fabricated a dc cloak, which is possible to be used in such potential applications. The dc cloak may be used to cloaking the landmines to make them invisible. Knowing the physical principle, we may also find ways to detect the cloaked landmines."

In the near future, the researchers plan to study three-dimensional ultra-thin dc cloaks and ultrathin cloaks for harmonic fields.

Explore further: One size cloaks all

More information: Wei Xiang Jiang, et al. "An ultrathin but nearly perfect direct current electric cloak." Applied Physics Letters 102, 014102 (2013). DOI: 10.1063/1.4774301

Journal reference: Applied Physics Letters search and more info website


Related Stories

One size cloaks all

November 21, 2012

A metamaterial invisibility cloak that can adapt to hide different sized objects is demonstrated by in Nature Communications this week. The findings represent a useful advance for more practical applications of metamaterial ...

New invisibility cloak hides objects from human view

July 27, 2011

For the first time, scientists have devised an invisibility cloak material that hides objects from detection using light that is visible to humans. The new device is a leap forward in cloaking materials, according to a report ...

Scientists create first free-standing 3-D cloak

January 26, 2012

Researchers in the US have, for the first time, cloaked a three-dimensional object standing in free space, bringing the much-talked-about invisibility cloak one step closer to reality.

Recommended for you

Unique insights into an exotic matter state

December 19, 2018

The properties of matter are typically the result of complex interactions between electrons. These electrically charged particles are one of the fundamental building blocks of nature. They are well researched, and theoretical ...

Focus on this: Team increases X-ray laser focusing ability

December 19, 2018

An X-ray free-electron laser (XFEL) is an X-ray produced by a beam of free electrons that have been accelerated almost to the speed of light. XFELs produce laser beams with exceedingly high peak power intensity, which makes ...

Magnetoresistance ratio enhancement in Heusler-based alloy

December 18, 2018

Magnetic field sensors can enhance applications that require efficient electric energy management. Improving magnetic field sensors below the picoTesla range could enable a technique to measure brain activity at room temperature ...


Adjust slider to filter visible comments by rank

Display comments: newest first

2.8 / 5 (16) Jan 17, 2013
Someone needs to coat the house behind me with it to give me back my view of the mountains :P
4.2 / 5 (10) Jan 17, 2013
it takes a while to realise that this cloak only masks direct current.
1 / 5 (10) Jan 17, 2013
Science fiction and UFO/alien stories are becoming science fact!? That is what I love about PhysOrg. (Stories about Yelp adding restaurant health inspection grades are not cutting edge.)
1.7 / 5 (11) Jan 17, 2013
A simple video demonstration would be nice.
1 / 5 (4) Jan 18, 2013
nothing good will come from this
1 / 5 (4) Jan 18, 2013
This is fantastic!!!!!!

Now, where's my goddam cold fusion?
2.1 / 5 (15) Jan 18, 2013
"The dc cloak may be used to cloaking the landmines to make them invisible. Knowing the physical principle, we may also find ways to detect the cloaked landmines."

Sorry , what kind of science is this ? Is this for the sake of humanity ? The stupidity is really astounding , cloaking land mines .
1.8 / 5 (5) Jan 18, 2013
those inter-continental nuclear ballistic missiles can now travel invisibly free...dangerous technology in the hands of determined terrorists.
1 / 5 (5) Jan 18, 2013
What I think about regarding cloaking advancements is the potential for an escalation of State/corporate sponsored acts of sabotage and State level paranoia. The last thing anyone needs is leaders of nuclear capable states desperately looking for a "boogyman".
2.1 / 5 (11) Jan 18, 2013
Ok ladies, I am just one step away from your locker room!
1 / 5 (3) Jan 18, 2013
Now, where's my goddam cold fusion?

If the cold fusion research would be as widespread, like the metamaterial research at the universities, you would see the results... Instead of it, the cold fusion researchers are


Admittedly, the sarcasm was a bit heavy-handed, but I was making exactly the same point.

Pointless(in the sense that it doesn't promote the common good), dangerous tech like this is endlessly and lavishly funded, while truly breakthrough tech like cold fusion --which would go a long way toward eradicating the conditions that make such cloaking devices attractive to paranoid, aggressive(but mostly just greedy) individuals, groups and states-- is given Zero attention or promotion.

The reasons for this sorry state of affairs is all too obvious, but that doesn't make it right. A fact that I continue to try to make plain.

3.7 / 5 (3) Jan 19, 2013
If the cold fusion research would be as widespread, like the metamaterial research at the universities, you would see the results.

If you remember back then cold fusion research WAS widespread - but people quickly realized that it din't work - so they dropped it again.

Metamaterials work and continue to produce results - so people continue to work on it.
That's just how research funding goes: show that something works and has potential and you get funding. You don't get funding for castles in the sky (especially if no one can even show a prototype)
1.1 / 5 (9) Jan 20, 2013

If you remember back then cold fusion research WAS widespread - but people quickly realized that it din't work - so they dropped it again.

From the font of ignorance. Just read the literature.
Whats that I hear from the Font of Ignorance?
"La la.La la I can't hear you."
Forget about the loser folks
Listen to Dr Edmond Storms. He knows his stuff.
1 / 5 (2) Jan 21, 2013
Don't the military have enough ways to kill people already without having them invisible too?
As has been said already in different ways dangerous tech in the wrong hands will all end up going bad. Enough toys in the tin soldiers tool box already. In fact far too many. Time to downsize I think not upgrade to another dimension of warfare that we don't need.
1 / 5 (2) Jan 21, 2013
And one other thing that crossed my mind was the amount of money being wasted on this unnecessary technology. If as much was spent on solving the current batch of global problems as is spent on further the war machines existence then we would actually have a happier and healthier existence instead of potentially more blood and gore.......especially from invisible mines and invisible fools.
The human race is sick in the head for permitting this sort of research ahead of all our other problems. But I guess there is no profit in peace boys and girls.
3 / 5 (2) Jan 21, 2013
From the font of ignorance. Just read the literature.

Did you even READ the link you just postd?

It's a list where EVERY article contains words like
"possible mechanisms"
There's a friggin' "Good morning America" segment listen on there as a source! That's not science. That's a quack list.
Not one of these is a source that claims to have anything working.

If that is what you call showing that something does work - you have GOT to be kidding.

And Stroms doesn't seem to be able to show anything, either.
1 / 5 (1) Jan 21, 2013
Guys. Read the article. This clokes DC (direct current) - not light.
It cloaks something from static electrical fields.
1 / 5 (1) Jan 21, 2013
I am not amused.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.