Tag Archives: invisibility cloak

Invisibility cloak designed for military renders anything behind it invisible

Credit: Hyperstealth Biotechnology.

A paper-thin material that requires no power source can render anything — be it soldiers, tanks, or ships — invisible as long as the object is behind the panel. The cloak not only hides things in the visible spectrum, but also bends ultraviolet, infrared, and shortwave infrared. The end result is a complete “broadband invisibility cloak.”

The smart material was designed by Hyperstealth Biotechnology, a Canadian firm that specializes in manufacturing camouflage gear for militaries across the world. Recently, the company filed for a patent that describes what may be the ultimate camouflage: the Quantum Stealth (Light Bending Material), otherwise known as the Invisibility Cloak.

Hyperstealth Biotechnology claims that it has developed 13 versions of the material, one of which works in any environment and in all four seasons.

According to Guy Cramer, CEO of Hyperstealth Biotechnology, the material works by bending light such that only the background is visible and the target, a person for example, is removed from view when behind the material. You can watch more than an hour’s worth of footage showing the technology in action on the company’s website.

The technology has already been tested by both the U.S. and Canadian military, which have confirmed that it also works against military IR scopes and thermal optics.

Real life invisibility cloaks are closer than we think

It might not be the Harry Potter’s invisibility cloak just yet, but researchers from Queen Mary University of London (QMUL) have successfully created a practical cloaking device using nano-size particles to make curved surfaces appear flat to electromagnetic waves.

Image credit Luigi La Spada

Image credit Luigi La Spada

In addition to its potential to someday lead to the creation of a real-life invisibility cloak, the team believes that the device could help broaden the potential ways that antennas can be tethered to platforms, allowing for the utilization of different sized and shaped antennas in awkward places.

“The design is based upon transformation optics, a concept behind the idea of the invisibility cloak,” said Yang Hao, a professor from QMUL’s School of Electronic Engineering and Computer Science and co-author of the study. “Previous research has shown this technique working at one frequency. However, we can demonstrate that it works at a greater range of frequencies making it more useful for other engineering applications, such as nano-antennas and the aerospace industry.”

The team took a curved surface roughly the size of a tennis ball and coated it with nano-particles to form seven unique layers, creating a material called a graded index nanocomposite medium. This material features varying electric properties in each layer depending on their position.

The result is the “cloaking” of the curved object by preventing it from scattering electromagnetic waves through the reduction of its electromagnetic signature.

The manipulation of surface waves seen in the new invisibility cloak is an important achievement for the development of numerous technological solutions and the advancement of many fields of science.

“We demonstrated a practical possibility to use nanocomposites to control surface wave propagation through advanced additive manufacturing,” said Luigi La Spada, also of QMUL and first author of the study. “Perhaps most importantly, the approach used can be applied to other physical phenomena that are described by wave equations, such as acoustics. For this reason, we believe that this work has a great industrial impact.”

Journal Reference: Surface Wave Cloak from Graded Refractive Index Nanocomposites. 15 July 2016. 10.1038/srep29363

invisibility cloak

Scientists make everyday objects invisible from multiple angles

invisibility cloak

Credit University of Rochester

Improving on the design of the famous Rochester Cloak, the first practical invisibility cloak, researchers used lenses to extend the invisibility effect over multiple, larger angles. Previously, the Rochester Cloak could make objects seem invisible over small angles only, and cloaking large objects would be impractical using it.

Don’t trust your eyes

To make an object seem invisible you need to preserve the appearance that light coming from a distant object has traveled in a straight line, even as the viewer moves. At every depth and every viewing angle, the background must change correctly or the observer will detect that something is wrong.

To accomplish this, the University of Rochester team’s new design uses a commercially available digital camera to scan the background and proprietary algorithms to encode the visual information. The system computes where all of those rays should end up in the future, then displays this information on a display, like an Apple iPad, placed right in front of the object we want to disappear. This is fundamentally different than previous cloaking attempts. 

“Many other approaches to invisibility cloaking try to guide light around an object,” said John C. Howell, lead author of the study. “We collect light rays at one position and display them at another position, making everything in between invisible.”

Unlike a single flat image recorded by your camera, the experimental setup encodes the pixel on the screen from multiple angles using lenticular lenses. The cloaking effect works even at an incredible 30 degrees angle.

It takes several minutes to scan and update the background behind the cloaked object, but the researchers claim making it real-time is technically possible, albeit at a lower resolution. For an object to become cloaked, its shape needs to remain fix and not deform.

For this particular demonstration, a spatial resolution of 20 pixels per inch for 51 possible viewing angles was achieved, as reported in the journal Optics Express. Adding more lenses to the array and using a higher-resolution display would increase both the number of viewing angles and the spatial resolution.

“Because the views are relatively close to each other it looks like it’s continuous,” said Joseph S. Choi of the University of Rochester. “The views change every half a degree, but in such a small way that it is hard to tell that it changed.”

The practical applications of this kind of cloak may seem obvious, but the researchers aren’t interested in fooling people objects aren’t there. It would be very difficult to conceal an object actively anyway.

Instead, the cloak could be useful in situations where hiding objects that the viewer knows are present is useful. For instance, a surgeon could look at a display and not see his hands, thus enabling the team to have an obstructed view of the operation. You could also place it on a blind spot inside your car so the driver can see through it, or even inside a home to act as a digital window.

“We usually think about cloaking in terms of spies, eavesdropping and Harry Potter’s cloak,” said Howell. “However, there are many situations where we don’t necessarily want to prevent someone from seeing something. Maybe an observer simply doesn’t like how something looks or needs to look through it. We’re not tricking them into thinking it’s not there, just enabling them to not see it.”

The team is also considering to make the cloak flexible so that it could be worn on the body.

“Since we already know what pixel needs to go where even if the detector and display deform or change in some way, making a wearable invisibility cloak is, in theory, possible based on our digital cloaking method,” said Howell. “It would, however, require heavy engineering and a lot of computational power to always know the position and orientation of the detector and display.”

(a) Schematic process. Charge-stabilized ​gold NPs exhibit single particle plasmons (SP) at 532 nm resonance. Particles glued into chains by ​CB molecules give CCPs (745 nm resonance). Illumination with femtosecond laser pulses (schematic b) connects chains by metal thread into strings, producing TCPs (1,100 nm resonance). (c) TEM images of NP chain gaps before and after femtosecond irradiation. (d) After adding ​CB molecules to the NPs, spectra are different with/without femtosecond laser irradiation. Single NP response is subtracted from spectra. As the threads develop, a spectral dip around the laser wavelength and a peak at the rising TCP emerge. (e) Numerical simulations of resonant six-NP-long chains display TCP mode and indicate the range of nanothread widths contributing to the signal in d.

Sewing an invisible cloak with lasers

Invisibility cloaking is already a reality, but don’t expect it works just like in Harry Potter. For the past decade or so, extremely promising advances have been reported. Using either metamaterials – artificial materials with properties typically not found in nature – or natural materials, scientists have devised all sorts of invisibility cloaks. All of these work, yet all of them are flawed in one way or the other. They render an object invisible only from one angle or only for a particular set of frequencies like microwaves and so on. In order to make a perfect invisibility cloak, one needs extremely advanced manufacturing methods. Scientists at University of Cambridge have devised a breakthrough technique that will allow us to build materials previously unavailable, including those that could be used to build invisibility cloaks – the genuine kind.

A laser that threads at the nanoscale

So, what do you see? You don’t see objects, trees or the sky, but the light that becomes reflected off each atom or molecules. Some frequencies are absorbed, while others are reflected eventually bouncing into our retinas, before eventually the brain taps in and decodes this information in manner we all recognize as sight. It’s not absurd to claim everything we see isn’t real, but a projection.

An invisibility cloak, in theory, has a surface geometry that refracts light in complex patterns and unusual directions. There are certain nanoparticles that can be used to refract light in this manner, but assembling them in the right pattern has proven so far impossible. The research by the team at University of Cambridge offers a viable solution for building this sort of metamaterials. They designed and built an unfocused laser that scatters light in millions of tiny needles. The laser is fired upon gold nanoparticles that line up in a string, then more strings are stacked ontop so eventually you wind up with a macroscopic piece of the metamaterial you can then use to fit a purpose.

(a) Schematic process. Charge-stabilized ​gold NPs exhibit single particle plasmons (SP) at 532 nm resonance. Particles glued into chains by ​CB molecules give CCPs (745 nm resonance). Illumination with femtosecond laser pulses (schematic b) connects chains by metal thread into strings, producing TCPs (1,100 nm resonance). (c) TEM images of NP chain gaps before and after femtosecond irradiation. (d) After adding ​CB molecules to the NPs, spectra are different with/without femtosecond laser irradiation. Single NP response is subtracted from spectra. As the threads develop, a spectral dip around the laser wavelength and a peak at the rising TCP emerge. (e) Numerical simulations of resonant six-NP-long chains display TCP mode and indicate the range of nanothread widths contributing to the signal in d.

(a) Schematic process. Charge-stabilized ​gold NPs exhibit single particle plasmons (SP) at 532 nm resonance. Particles glued into chains by ​CB molecules give CCPs (745 nm resonance). Illumination with femtosecond laser pulses (schematic b) connects chains by metal thread into strings, producing TCPs (1,100 nm resonance). (c) TEM images of NP chain gaps before and after femtosecond irradiation. (d) After adding ​CB molecules to the NPs, spectra are different with/without femtosecond laser irradiation. Single NP response is subtracted from spectra. As the threads develop, a spectral dip around the laser wavelength and a peak at the rising TCP emerge. (e) Numerical simulations of resonant six-NP-long chains display TCP mode and indicate the range of nanothread widths contributing to the signal in d.

The gold particles were electrically connected to form a strand, while spacer molecules called cucurbiturils (CBs) were used to  form a scaffold that keeps the particles just the right distance apart so that ripples of electrons can flow along the surface of the chain.

This is only the first step towards building metamaterials that not too long ago would have been deemed impossible. Findings appeared in Nature Communications.

Touch invisibility cloak prevents objects from being felt

With the finger or a force measurement instrument, no information is obtained about the bottom side of the material. Credit: T Bückmann / KIT

In the past years, several types of invisibility cloaks have been developed, hiding objects not only from light, but also from sound and even heat. But this is the first time an invisibility cloak for touch has been developed.

Recently, we’ve written quite a lot about invisibility cloaks – how they work, how they can be improved, and what real life applications they have (aside from being really cool) – like for example protecting cities from earthquakes (yeah, really). But what about a  “touch invisibility cloak” ? Naturally, it is constructed very differently – based on a metamaterial that consists of a polymer with a special structure.

“We build the structure around the object to be hidden. In this structure, strength depends on the location in a defined way,” explains Tiemo Bückmann, KIT, the first author of the article. “The precision of the components combined with the size of the complete arrangement was one of the big obstacles to the development of the mechanical invisibility cloak.”

The metamaterial in case is actually in a crystalline material, built with extreme sub-micrometer accuracy; it basically consists of needle-shaped cones, whose tips meet. The size of the contact points is calculated precisely to reach the mechanical properties desired. The resulting structure is built in such a way that a finger or a measuring instrument cannot feel its way through it.

“It is like in Hans-Christian Andersen’s fairy tale about the princess and the pea. The princess feels the pea in spite of the mattresses. When using our new material, however, one mattress would be sufficient for the princess to sleep well,” Bückmann explains.

So far, this is pure research – no end goal in sight. However, since it paves the way for producing materials with freely selectable mechanical properties, it could have a myriad of applications. The first that pop to mind are comfier mattresses or rugs under which you can sneak a cable or two and not feel them; however, investing in such a high-end technology for this type of results is not something doable at the moment.

Journal Reference:
T. Bückmann, M. Thiel, M. Kadic, R. Schittny, M. Wegener. An elasto-mechanical unfeelability cloak made of pentamode metamaterials. Nature Communications, 2014; 5 DOI: 10.1038/ncomms5130

Invisibility cloak could help protect cities from earthquakes

French researchers say they are close to developing seismic ‘invisibility cloaks’ which would cancel out potentially hazardous earthquake shockwaves, protecting key buildings or even entire cities.

Destroyed buildings in the aftermath of the Japan 2011 earthquake. The system proposed here could protect key areas like the Fukushima nuclear plant, or even entire cities. Via BBC.

Nuclear power plants especially, and potentially entire cities could be cloaked using this technology – if the researchers’ theories are true (which seems highly likely). They believe that by drilling boreholes in a precise pattern into the ground, they could divert seismic waves and averting any negative results. They’ve already teamed up with geo-engineering company Ménard to build upon their results.

“You can build on this knowledge to create an invisibility cloak which will actually protect a specific site from seismic waves,” says the leader of the team, physicist Sebastien Guenneau, who published the work in Physics Review Letters in late March.

They are currently testing to see if they can protect an area the size of a football field from an earthquake.

Invisibility cloaks and earthquakes

In the early 2000s John Pendry from Imperial College London, shook the world when he proposed an invisibility cloak. Several years later, in 2006, he actually built one, but it wasn’t invisible in visible light, but in microwaves. The big problem when trying to develop invisibility cloaks is the sheer difference in size between light waves and real life objects. However, seismic waves are relatively similar in size to large objects like buildings or even cities. This technology works on the same basic principles as proposed invisibility cloaks – but this approach is incredibly creative, a pure example of out-of-the-box scientific thinking.

Seismic waves are basically acoustic waves – but instead of propagating through air, they propagate through the ground. They therefore share a similar behavior (in some cases) with light waves. Invisibility cloaks work by developing materials with geometric structures smaller than the wavelength of the light they are deflecting. In the case of the earthquakes, the holes are boreholes in the ground. The team calculated that for earthquake wavelengths of around 1.5 meters, the boreholes would need to be 30 cm wide and spaced 1.73 meters apart. How this works is that the holes scatter the incoming waves, and if you place the boreholes just right, the scattering makes the waves to cancel each other out. But there are several issues with this approach.

First of all, you can’t really control the properties of soil – like you can do to a material in the lab. Soils vary laterally, and are dynamic in nature.

“Soil is a different story. Its properties are difficult to characterize, and depend on different things, such as the weather! It makes the mathematical models much more difficult.”

Other researchers have toyed with a different approach for an earthquake invisibility cloak, but when the French scientists first come up with this idea in 2010, they were ridiculed by many. However, they stuck to their idea and convinced Stephane Brûlé, an open-minded geo-engineer to join them. Luckily enough,  Brûlé has a company -Ménard, and he was able to jump start the project.

Practical results

In 2012, they got the first practical results. After looking carefully through the weather prognosis, they chose three days of consistent sunny weather in August, near Grenoble, at the foot of the Alps. They measured the seismic waves naturally hitting the area, and after that, they dug their holes: three rows of five meter deep boreholes. They then stopped an measured again – it worked.

Sebastien Guenneau. Leave him alone ladies, he has work to do!

Just as the model predicted, most of the earthquake’s energy was scattered – only 20% of the earthquake’s energy actually reached the surface in the protected area!

“It’s interesting because these are the first experimental results on this topic,” says physicist Boris Kuhlmey who studies electromagnetic metamaterials at the University of Sydney. But he points out the bore pattern the team used would only reflect seismic waves of a specific frequency. “If your aim is to stop an earthquake you don’t get to choose the frequency,” he says.

That’s the second problem with this approach. While you can study a statistical distribution of earthquake frequencies and make a very educated guess (in some cases more than others), you might still be off in your estimates. But Guenneau developed a mathematical model that might provide a “zero stop band”, which can stop a wide range of earthquake waves.

“That would be really key to get it to work well. Maybe it’s possible, on the scale of a city, to diminish the impact of an earthquake considerably,” says Kuhlmey.

Now, they’re set to try it out for good – they’re going to simulate really big earthquakes (magnitude 6) around their test site, which will be protected by boreholes. The boreholes are arranged in a ring with a diameter of about 200 meters. To say that I’m really looking forward to the results is an understatement.

“It would be a dream for me to see this done for real one day, not just tests,” muses Guenneau. In the meantime he is already turning his skills to other problems, such as tsunami control. “Imagine some columns of wood, 200 m from the sea shore, arranged in a similar fashion to the bore holes in the seismic experiments. The effect will be that you deflect the tsunami to a non-sensitive coastal area.”


Invisibility cloak

Human-sized invisibility cloak makes use of magic trick to hide large objects

Invisibility cloaks have become the object of study for many research institutes out of a number of considerations. There’s the simple scientific thrill of breaching the SciFi barrier, something every researcher dreams of. Then of course, there’s always the corporate and military tail that always likes to meddle with concepts that shine with the possibility of profit or strategic edge, and is always quick to offer incentives – money. Advancements in this direction have been nothing short of mind boggling, as we’ve reported in the past about a few working models, developed at great pace in the past few years alone. The latest invisibility cloak comes from scientists at University of Rochester in New York, and differentiates itself by extremely simple design, reminiscent of tricks magicians use on stage to hide objects, and its high potential for scaling the cloak for large objects like the human body or even satellites.

Most invisibility cloaks today work by exploiting two core ideas: transformation optics (bending light around a region of space to make it look as if it weren’t there) and metamaterials ( synthetic substances with optical properties that can’t be found anywhere else in nature designed specifically for cloaking). The ultimate goal is to produce an invisibility cloak that can hide a human from optical observations, Harry Potter-cloak style. This hasn’t been possible as of now, though.

The problem lies in compromise. So far, cloaks have been made that can hide objects in 3-D only at a single microwave frequency. Then, there are cloaks that can hide objects over a wide range of optical frequencies, but only work from a certain viewing angle. Apparently, you can’t have both – not just yet at least.

Invisibility cloakThe  University of Rochester cloak unveiled just recently had to make a compromise as well, and the researchers chose settled for a limited viewing angle for their device. It makes up for it, however, by functioning over the entire optical spectrum and, most importantly, through its potential of being scaled for extremely large objects.

Besides, their approach is extremely simple and doesn’t require expensive and difficult to implement metamaterials. To cloak, the device makes use of an array of lenses or mirrors that steer light around the region of space they want to hide. Mirrors can be fashioned into any size, easily and cheaply.

To demonstrate the cloaking ability of their device, the researchers cloaked a chair with a trash can behind it. “This volume is sufficient to cloak a human, albeit with not as much convenience as Harry Potter’s cloak,” say John Howell at the University of Rochester in New York.

Can their work have any potential application? The researchers seem to think so. Despite being unidirectional, the cloak can be scaled to very large sizes and could have value, for example, in cloaking satellites in mid- to high-earth orbit, making them optically invisible from Earth-based observations. A system might be employed to constantly shift the angles of the mirrors as the satellite swirls through orbit.

Findings were reported in a published paper.

A cagelike cloak surrounds a plastic sphere in an echo-free chamber. The cloak shielded the sphere from detection at a particular sound frequency, the first time a three-dimensional object has been cloaked from sound waves. Credit: L. Sanchis et al

Sound cloak devised that works for 3-D objects

After scientists have devised materials that rend objects optically invisible, researchers in Spain have developed a method that allowed them to cloak 3-D objects from sound waves for the first time. While sound cloaking has been demonstrated before, this was the first time that a full 3-D object was concealed. The findings might help engineers build buildings and machinery with considerable noise reduction to help battle noise pollution, and of course aid in the design of submarines and ships that avoid enemy sonar detection.

A cagelike cloak surrounds a plastic sphere in an echo-free chamber. The cloak shielded the sphere from detection at a particular sound frequency, the first time a three-dimensional object has been cloaked from sound waves. Credit: L. Sanchis et al

A cagelike cloak surrounds a plastic sphere in an echo-free chamber. The cloak shielded the sphere from detection at a particular sound frequency, the first time a three-dimensional object has been cloaked from sound waves. Credit: L. Sanchis et al

What’s important to note about the findings, however, is that the cloaking was achieved using readily available, commercial materials, instead of synthetic, lab-built meta-materials that are very expensive and difficult to manufacture. With this in mind, the present sound cloak is actually a multi-layered plastic shell.

What we see is actually light bouncing off objects into our retina – in a way, we’re not actually seeing objects themselves, but their reflections. Invisibility cloaks take advantage of this simple phenomenon and work by steering off the scattering of light around the object. The same effect can be achieved for a sound cloak if you steer away sound waves. The main drawback however is that this requires highly complex materials for this to work.

The researchers at the Polytechnic Institute of Valencia in Spain chose to walk on an alternate route, and instead of preventing sound waves from hitting an object (in this case, an 8-inch sphere), they devised a cloak to eliminate the scattered waves left in the sphere’s wake.

Muting objects with a sound cloak

Using a sophisticated computerized model that told them what kind of design they needed to build around the sphere, the team of scientists lead by José Sánchez-Dehesa built a structure comprised of 60 rings of various sizes that form a cagelike structure around the sphere. Simulations showed that the scattered sound waves bouncing off the sphere and the cloak would interfere and cancel each other out, essentially rending them mute and  undetectable.

To test the sound cloak in real life, the sphere-ringed cloak pair was  positioned on the ceiling of an echo-free chamber, while a speaker that was pointed at it played a range of sound frequencies.  For most frequencies, the sphere scattered an easily detectable amount of sound. But at 8.55 kilohertz — an audible high pitch — the cloaked sphere became imperceptible to the sensors behind it.

This means that the sound cloak works, but it’s still far from being a complete solution. For one,  the cloak works only for a narrow frequency range coming from one direction, so if the speaker would have been positioned an inch farther to the right, the cloaking wouldn’t have worked. Then, it has to be custom designed and built for each object, which is quite a hassle. With this in mind, Sanchez-Dehesa and colleagues plan to broadband and multidirectional cloaks.

While submarines and ships will still have a long way to go until they can avoid enemy detection using such technology, the researchers claim that their findings are far from being useless, even in their present state. Structures capable of manipulating a specific sound frequency from one direction could help minimize noise pollution from a congested highway. “The cloak does one thing quite well, with a very simple structure,” said Steven Cummer, an electrical engineer at Duke University, who was not involved in the study.

Findings were reported in the journal Physical Review Letters.

New invisibility cloak takes things to the next level

It may be a little off to talk about invisibility when we’re not even in the visible spectrum, but ‘invisibility cloak‘ sounds just to awesome not to use it. Using a new kind of cloak that uses a very thin multilayer dielectric coating made of natural material (as opposed to metamaterials which are often used), researchers from Michigan University demonstrated better cloaking efficiency than a similarly sized metamaterial cloak designed with a different technology.


The materials they used are relatively simple – dielectric materials such as ceramics having differing dielectric permittivity (the measure of resistance created when forming an electric field; usually with invisibility studies, researchers use metamaterials – which are artificially developed and have different characteristic to anything found in nature. Yet using this simple technique, they were able to cloak larger cylindrical objects more effectively than ever before, with any kind of material.

The so-called metascreen they created has a fishnet like structuer, covering an 18 cm cylindrical rod from microwaves. The reason why we see things is because light bounces on and off of them; previous such technologies used metamaterials to divert, or bend, the incoming waves (including light) around an object, this uses an ultrathin metallic metascreen to cancel out the waves as they are scattered off the cloaked object.

“When the scattered fields from the cloak and the object interfere, they cancel each other out and the overall effect is transparency and invisibility at all angles of observation,” said co-author of the study Professor Andrea Alu.

According to their report in the Applied Physics Letters article, Semouchkina and Wang used a very thin multilayer dielectric coating and compared it with cloaks of a similar size which use a different principle, called transformation optics.

“The new cloak demonstrated better cloaking efficiency than did a similarly sized metamaterial cloak designed by using transformation optics relations,” said Semouchkina.

Not only does the new cloak outperform previous cloaks, which caused more reflection and more shadows, as well as distortion of the electromagnetic waves, but it is also more scalable and cheaper to produce; about 8-9 times cheaper, they noted.

“The multi-layer dielectric cloak could easily be scaled to work in a variety of frequency ranges,” Semouchkina said. “The design procedure developed in this work could be used to further advance the cloak parameters and for adjusting it to practical needs.”

Invisibility cloak now a reality – perfect demonstration

It may still be a while until we get our Harry Potter-like invisibility cloak, but researchers have managed, for the first time, to render a cylinder invisible to microwaves.

Science, not magic

Invisibility is a notion that fascinated humans for centuries or even millennia; it’s just one of those things which never gets old, regardless of the period. We now know that, since we see objects because light bounces of their surface, if we want to make something invisible, you have to prevent it from reflecting light – simple in theory, extremely hard to practice. However, in 2006, invisibility became more of a practical matter, with the suggestion that artificially structured metamaterials could enable a new electromagnetic design paradigm – something which is now called transformation optics.

Since this term was coined, transformation optics has developed significantly – so greatly that it forced researchers to make simplifying approximations to achieve even a subset of the desired functionality. The problems with most devices spawned here – despite many ‘invisibility cloaks’ being tested successfully, they all reflected some of the incident light, which made the illusion incomplete.

This new research, published in Nature Materials showed how to pull that trick off flawlessly. Nathan Landy & David R. Smith teamed up in an effort to take things to the first level. Despite the perfection of their method, this only works from one direction, and with microwaves. But this is no spherical cow approach – it holds great promise for the future.

Where’s my invisible cloak?

The material structures which can create such remarkable features are all but impossible to create, and again, some approximations were made. So when you would use your invisibility cloak, while you would see the image behind your object, you would see it distorted, mostly darkened – not very useful to make something invisible, but noticeable.

Previous example of invisibility cloak. Source

Now, Prof Smith and his Duke colleague have used a different approach. They have reworked the edges of the cloak, ensuring the light passes with around the cloak with completely no reflections. The trick was to used a diamond shaped cloak with properties carefully matched at the diamond’s corners.

“This to our knowledge is the first cloak that really addresses getting the transformation exactly right to get you that perfect invisibility,” Prof Smith told BBC News.

However, it was a “win some lose some” approach. While the illusion is perfect, it only works from one direction.

“It’s like the card people in Alice in Wonderland,” Prof Smith explained. “If they turn on their sides you can’t see them but they’re obviously visible if you look from the other direction.”

Lengthy problems

This wouldn’t even be the biggest problem. It would be extremely hard to make the device function at optical wavelengths, which are much larger than those of the microwaves. However, this could be extremely useful in many applications, principally telecommunications and radar, for which it could greatly improve the performance.

“The cloak we demonstrated in 2006 as a kind of microwave device would be very poor, but this one gets us to something that could be potentially useful,” Prof Smith said. “I think it’s something that a lot of people can build on. Everything in this field is going to come down to what you can make, what you can design. And I think this steps up the design.”