‘Cloaking’ device uses ordinary lenses to hide objects across range of angles : NewsCenter

‘Cloaking’ device uses ordinary lenses to hide objects across range of angles : NewsCenter: “This is the first device that we know of that can do three-dimensional, continuously multidirectional cloaking, which works for transmitting rays in the visible spectrum..."

In order to both cloak an object and leave the background undisturbed, the researchers determined the lens type and power needed, as well as the precise distance to separate the four lenses. To test their device, they placed the cloaked object in front of a grid background. As they looked through the lenses and changed their viewing angle by moving from side to side, the grid shifted accordingly as if the cloaking device was not there.  There was no discontinuity in the grid lines behind the cloaked object, compared to the background, and the grid sizes (magnification) matched.

Elastic Cloaking Material Makes Objects “Unfeelable” - Scientific American

Elastic Cloaking Material Makes Objects “Unfeelable” - Scientific American: The unfeelability cloak is a so-called pentamode metamaterial, an artificial structure that, despite being a solid, can behave like a fluid; although difficult to compress, its shape is otherwise easy to shift. The specific material the researchers devised is a three-dimensional hexagonal lattice reminiscent of a honeycomb, with the rods making up this lattice wider at their middles than at their ends...

The unfeelability cloak does have limits. For instance, the dimensions of the cloak's components have to be designed to specifically match whatever the cloak is hiding. Furthermore, although unfeelability cloaks can hide objects from some pokes and prods, it cannot protect against all of them—one can push on a cloak strongly enough to break it and feel the object it hides.

Elastic invisibility cloak hides materials from touch sense

Elastic invisibility cloak hides materials from touch sense: The metamaterial is a crystalline material structured with sub-micrometer accuracy. It consists of needle-shaped cones, whose tips meet. The size of the contact points is calculated precisely to reach the mechanical properties desired. In this way, a structure results, through which a finger or a measurement instrument cannot feel its way.

In the invisibility cloak produced, a hard cylinder is inserted into the bottom layer. Any objects to be hidden can be put into its cavity. If a light foam or many layers of cotton would be placed above the hard cylinder, the cylinder would be more difficult to touch, but could still be felt as a form. The metamaterial structure directs the forces of the touching finger such that the cylinder is hidden completely...

Researchers build optical invisibility cloak for a diffusive medium

Researchers build optical invisibility cloak for a diffusive medium: ...The tank was filled with a white, turbid liquid. Objects inside cast a visible shadow onto the tank wall. Simple metal cylinders or spheres of a few centimeters in diameter were used as test objects... To pass the light around the object, the researchers applied a thin shell made of the transparent silicon material PDMS, to which a certain concentration of light-scattering melamine microparticles was added. The silicon/melamine shell caused a quicker diffusion than in the environment and, thus, passed the light around the objects...

"Ideal optical invisibility cloaks in air have a drawback... They violate Albert Einstein's theory of relativity that prescribes an upper limit for the speed of light.  In diffuse media, in which light is scattered several times, however, the effective speed of light is reduced. Here, ideal invisibility cloaks can be realized."

Researchers design a new structure that absorbs all sound

Researchers design a new structure that absorbs all sound: In their work, the researchers have demonstrated how the designed structure achieves extraordinary sound absorption using an apparently contradictory strategy: the sound attenuation increases when the quantity of absorbent material is reduced. This way, a totally reflective surface becomes a perfect absorbent despite the fact that, for the most part, there is no material that absorbs sound.

Genetic algorithm used to design broadband metamaterial | KurzweilAI

Genetic algorithm used to design broadband metamaterial | KurzweilAI: "...this is the first that can cover a super-octave [more than doubling] bandwidth in the infrared spectrum...”

The new metamaterial is actually made of layers on a silicon substrate or base. The first layer is palladium, followed by a polyimide (plastic) layer and a palladium screen layer on top. The screen has elaborate, complicated cutouts — sub-wavelength geometry — that serve to block the various wavelengths. A polyimide layer caps the whole absorber...

This evolved metamaterial can be easily manufactured because it is simply layers of metal or plastic that do not need complex alignment. The clear cap of polyimide serves to protect the screen, but also helps reduce any impedance mismatch that might occur when the wave moves from the air into the device...

How to create a large-area visible-light invisibility cloak | KurzweilAI

How to create a large-area visible-light invisibility cloak | KurzweilAI: To create the material, they used a nanotransfer printing technique that creates metal/dielectric composite films. These are stacked in a 3-D architecture to achieve nanoscale patterns for operation in the visible spectral range. Control of electromagnetic resonances over the 3-D space by structural manipulation allows precise control over propagation of light...

...he sample they created covers about 4 square centimeters...

Acoustic Cloaking Device Hides Objects from Sound | Duke Pratt School of Engineering

Acoustic Cloaking Device Hides Objects from Sound | Duke Pratt School of Engineering

The acoustic cloaking device works in all three dimensions, no matter which direction the sound is coming from or where the observer is located...

In the case of the new acoustic cloak, the materials manipulating the behavior of sound waves are simply plastic and air. Once constructed, the device looks like several plastic plates with a repeating pattern of holes poked through them stacked on top of one another to form a sort of pyramid...

How To 3-D Print Your Own Invisibility Cloak | Popular Science

How To 3-D Print Your Own Invisibility Cloak | Popular Science: Duke University engineer Yaroslav Urzhumov has designed a plastic disk that makes a small object placed in its hollow center invisible to frequencies from 9.7 to 10.1 GHz (close to the range used by radar speed guns). Holes in the doughnut-shaped cloak can eliminate an object’s shadow and decrease its ability to scatter light. In effect, the cloak guides the microwave beams around the object so they can’t bounce back—rendering it invisible.

How to Build a Time Cloak with Mirrors | MIT Technology Review

How to Build a Time Cloak with Mirrors | MIT Technology Review:  His idea is to use one set of mirrors to divert light through an extra distance before it reaches the clock and another set of mirrors that diverts light through a similar distance after it has hit the clock.

This extra distance essentially slows down the lights before it hits the clock. After it has been reflected, the light can be speeded up by avoiding the diversion so that it does not travel the extra distance.

Time cloak hides events by splicing them movie style

Time cloak hides events by splicing them movie style: Time cloaks work by slowing down light in an optical fibre, creating a gap in the beam. Any outside light that enters the hole becomes cloaked when the original beam is sped up...

A diffraction grating stretches out a laser beam, producing a series of gaps. Pulses of light sent along the fibre at the same time slot into these. A second grating then closes the holes, hiding the pulses from the intended receiver. There is now no record that the pulses ever traversed the fibre... This string of cloaks can hide up to 1.5 gigabytes per second.

Sound cloaks enter the third dimension | Matter & Energy | Science News

Sound cloaks enter the third dimension | Matter & Energy | Science News: ... the researchers came up with a design made up of 60 rings of various sizes that form a cagelike structure around the sphere. Simulations indicated that sound waves scattering off the sphere and the ringed cloak would interfere with each other and cancel out.

Because the cloak did not need to steer sound waves in complicated ways, Sánchez-Dehesa and his team built it out of plastic with the help of a 3-D printer.  They hung their creation from the ceiling of an echo-free chamber, pointed a speaker at it and 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.

‘Metascreen’ forms ultra-thin invisibility cloak

‘Metascreen’ forms ultra-thin invisibility cloak: The trick: a new, ultrathin layer called a “metascreen,” made by attaching strips of 66-micron-thick copper tape to a 100-micron-thick, flexible polycarbonate film in a fishnet design. It was used to cloak (hide) an 18 cm cylindrical rod from microwaves...

Previous cloaking studies have used metamaterials to refract (bend) the incoming waves around an object. The new “mantle cloaking” method uses instead an ultrathin metallic metascreen to cancel out the waves as they are scattered off the cloaked object...

Chinese Physicists Build "Ghost" Cloaking Device | MIT Technology Review

Chinese Physicists Build "Ghost" Cloaking Device | MIT Technology Review: Instead, their device takes the light scattered from the apple and distorts it to look like something else such as a banana.  The symmetry of the effect–light is scattered on both sides of the apple–mean that this approach produces two “ghost” bananas, one on each side of the apple...
The big advantage of this approach is that it can be achieved now with existing technology...
They then go on to build a working prototype using concentric cylinders of split ring resonators that operates in 2 dimensions...

Seafloor Platform 'Cloaks' Big Ocean Waves : Discovery News

Seafloor Platform 'Cloaks' Big Ocean Waves : Discovery News: Alam found that if he used a rippled sheet of material, one that had a specific set of heights and lengths, and put it on the ocean floor, the energy from deep water would make the internal waves in the thermocline more energetic, but cancel out surface waves. That makes for calm water on the surface.

BBC News - Invisibility cloaking in 'perfect' demonstration

BBC News - Invisibility cloaking in 'perfect' demonstration: So someone would not see a cloaked object but rather the scene behind it - however, the reflections from the cloak would make that scene appear somewhat darkened.

Now, Prof Smith and his Duke colleague Nathan Landy have taken another tack, reworking how the edges of a microwave cloak line up, ensuring that the light passes around the cloak completely with no reflections.

The trick was to use a diamond-shaped cloak, with properties carefully matched at the diamond's corners, to shuttle light perfectly around a cylinder 7.5cm in diameter and 1cm tall.

An Invisibility Cloak With An On-Off Switch

An Invisibility Cloak With An On-Off Switch: What makes this possible is a process known as electromagnetically induced transparency--a phenomenon in which certain materials become transparent when zapped by light from two carefully tuned lasers...

If the frequencies of the lasers are close together, they can be tuned in a way that makes them interfere destructively. And when this happens, their ability to excite electrons cancels out.

When this happens, the laser photons suddenly pass through the material unimpeded, sometimes at dramatically reduced at speeds (which is how experiments that stop light are performed)...

Their trick is to use atoms that can exist in five electronic states rather than three. This allows additional control over the refractive index called magneto-electric cross-coupling.


The bottom line is that this allows an external magnetic field to modulate the change in refractive index.

'Schrödinger's Hat' Uses Invisibility to Measure Quantum World

'Schrödinger's Hat' Uses Invisibility to Measure Quantum World: Mathematicians now suspect quirks in energy-cloaking metamaterials could be exploited to create powerful quantum probes called "Schrödinger's hats." Such probes might record extremely subtle signals that would otherwise be scrambled by any attempt to measure them.
Yet no ideal metamaterials exist. All slightly betray the existence of objects they conceal, and none completely divert a wide range of energetic frequencies. Some metamaterials even resonate like tuning forks at specific frequencies, sounding like an alarm instead of hiding something. Where some scientists see flaws, however, Greenleaf and his colleagues see opportunity. If the amount of energy going through a metamaterial and the amount of energy coming out are almost perfectly balanced, the resonating metamaterial should trap a signal that describes the environment it was just in. Over time the signal would leak out, allowing researchers to record it.

Thousands of invisibility cloaks trap a rainbow

Thousands of invisibility cloaks trap a rainbow: "In our array, light is stopped at the boundary of each of the cloaks, meaning we observe the trapped rainbow at the edge of each cloak. This means we could do 'spectroscopy on-a-chip' and examine fluorescence at thousands of points all in one go."

The 25 000 invisibility cloaks are uniformly laid out on a gold sheet, with each having a microlens that bends light around itself, effectively hiding an area in its middle. As the light squeezes through the gaps between each of the cloaks, the different components of light, or colours, are made to stop at ever narrower points, creating the rainbow.

To construct the array of invisibility cloaks, a commercially available microlens array, containing all of the individual microlenses, was coated with a gold film. This was then placed, gold-side down, onto a glass slide which had also been coated with gold, creating a double layer. A laser beam was directed into the array to test performance of the cloaks at different angles.

Cloak of invisibility: Engineers use plasmonics to create an invisible photodetector

Cloak of invisibility: Engineers use plasmonics to create an invisible photodetector: It may not be intuitive, but a coating of reflective metal can actually make something less visible, engineers at Stanford and UPenn have shown. They have created an invisible, light-detecting device that can "see without being seen."
At the heart of the device are silicon nanowires covered by a thin cap of gold...
By carefully designing their device – by tuning the geometries – the engineers have created a plasmonic cloak in which the scattered light from the metal and semiconductor cancel each other perfectly through a phenomenon known as destructive interference.
The rippling light waves in the metal and semiconductor create a separation of positive and negative charges in the materials – a dipole moment, in technical terms. The key is to create a dipole in the gold that is equal in strength but opposite in sign to the dipole in the silicon. When equally strong positive and negative dipoles meet, they cancel each other and the system becomes invisible.