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February 8th, 2011

Two groups find cheaper, easier route to ‘cloaking’ in visible light

Published on February 8th, 2011 | By: pwray@ceramics.org

A pink object under the cloak becomes invisible. Credit: SMART Center.

Last week I mentioned that someone has found a new, cheap way to optically “hide” objects (other than the metamaterials route). Via Gizmag, I heard about the the work of two groups who, in parallel, are using calcite crystals to make objects seem to disappear — and its one of those things where you immediately say, “Why didn’t I think of that?”

Calcite, boron nitride, silicon carbide and other crystals (and some plastics) are known for having birefringence (aka, double refraction). Briefly put, birefringence causes a ray of light to split into two rays. The property is already used in LCDs and other optical and electronics applications.

What’s novel is the two groups — one from the SMART Center and the other collaboration between researchers at University of Birmingham (U.K.), Imperial College, London and Technical University of Denmark — is to put two prism-shaped pieces of calcite next to each other, aligning their optical axes. If the resultant wedge (the SMART group used a 38mm X 10mm X 2mm wedge) is then put over an object, it appears to disappear when viewed from either side of the wedge, and the two-dimensional effect works for macroscopic objects “larger than 3500 free-space wavelengths, inside a transparent liquid environment.  Its working color range encompassing red, green and blue light has also been demonstrated.”

The U.K./Denmark collaborative group also were able to achieve the effect in air. One of these researchers, Shuang Zhang, lead investigator from the University of Birmingham’s School of Physics and Astronomy, predicted bigger things ahead. He says:

“By using natural crystals for the first time, rather than artificial metamaterials, we have been able to scale up the size of the cloak and can hide larger objects, thousands of times bigger than the wavelength of the light. Previous cloaks have succeeded at the micron level (much smaller than the thickness of a human hair) using a nano- or micro-fabricated artificial composite material. It is a very slow process to make these structures and they also restrict the size of the cloaking area. 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.”

The SMART groups work is published in Physical Review Letters, and the U.K./Denmark group’s work is published in Nature Communications.

Physics World was particularly impressed with the SMART Center’s work, naming it one of the “Top 10 breakthroughs of 2010.”

Here is a video from featuring Zhang showing how the calcite crystal can make part of a panda disappear:

 


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2 Responses to Two groups find cheaper, easier route to ‘cloaking’ in visible light

  1. Sankaravelayudhan Nandakumar says:

    OUT COME OF 2010 NOBEL PRIZE IN PHYSICS :
    Graphene: Boron nitride sandwich with magnetic field levitated –invisible cloaking hydrodynamics unveils electronic potential in Electric and Maglev trains
    Citation:Possible dual role one as a conductor and another as an insulator may be possible with piezo electric crystal by sand witching by magneticfield levitated combinations as well as by John Pendry’s invisible cloaking dynamics.
    A breakthrough in graphene research which could pave the way for new smaller, faster, more powerful computer chips. Graphene has been hailed as a “miracle material” which could revolutionize materials science because of its unique properties.However with induction maglev magnetic properties by a possible piezoelectric properties a better sand witch could be made along with invisible metamaterials tricky invisible cloaking dynamics says Sankarvelayudahn nandakumar which also act as a sliding screen by initiating a dual reaction along with super conductive nitrogen gas reactive systems if possible.
    Graphene encapsulated within boron nitride offers the best and most advanced platform for future graphene electronics. It solves several nasty issues about graphene’s stability and quality that were hanging for long time as dark clouds over the future road for graphene electronics. “Creating the multilayer structure has allowed us to isolate graphene from negative influence of the environment and control graphene’s electronic properties in a way it was impossible before, The structure chosen in this research has the BN-graphene-BN sandwich attached to a substrate and topped with a second graphene layer. “Insulating behaviour in graphene was never observed because of charged impurities on graphene surface. These impurities are responsible for formation of so-called electron-hole puddles. Within each puddle graphene is a good conductor and a network of such puddles makes graphene sheet conducting too. second graphene layer screens these impurities making puddles much shallower and turning first layer into insulator. Graphene becomes insulating in our experiments at rather low temperatures, and when the concentration of charge carriers in the graphene sheet is quite low. At high concentrations it is a pretty good conductor at any temperature, including at very low temperature. Rather than grow graphene and boron nitride on a substrate, the sandwich was built by hand. The famous ‘sticky tape’ method to isolate graphene and thin flakes of boron nitride and then transfer them on top of each other.
    Graphene is a chicken wire-like lattice of carbon atoms that can conduct electricity because a thin cloud of electrons hover either side of the mesh. Boron has a slightly smaller atom than carbon, and nitrogen a slightly larger atom. Together they can also form a chicken wire mesh. “Boron nitride a similar lattice constant [atom spacing] to graphene and the same hexagonal structure. Graphene has six carbon atoms in a ring,”. “Boron nitride has six atoms in a ring alternating boron-nitrogen-boron-nitrogen. It is know as ‘white graphene’ because it is white in bulk.
    Our vision is to have electronic devices which can be integrated with your body or clothing, or computers which can be bent or rolled up and put away, but also conveying signals through magneticfield levitated tracking says Sankravelayudhan Nandakumar.This may be a warning signal for mobile using drivers of electric train with infraray detecting the Red signals with an alarm to warn the drivers while they are are in mobiles to ward off catastrophic evens.
    j.pendry@imperial.ac.uk,news@nature.com
    drsmith@ee.duke.edu
    mobile@imperial.ac.uk
    1) Graphene: Boron nitride sandwich with magnetic field levitated –invisible cloaking hydrodynamics unveils electronic potential in Electric and Maglev trains [Incident: 111017-000017] news@nature.com
    2)OUT COME OF 2010 NOBEL PRIZE IN PHYSICS : [Incident: 111017-000022]news@nature.com

  2. Dan says:

    I am hopeful that better demonstrations will be available soon. Neither the photo nor the video convincingly display that the scene beyond the cloaked object appears unperturbed. The video comes close, using a toy bear as background texture, but the prism structure infront of the bear simply goes from transparent to non-transmitting, and it is not clear that there is any object within that prism structure.
    A more convincing display would be to show the bear, show the bear through the prism structure, and then lower something into the “cloaked” region between the prisms while showing real-time a lack of disturbance of the far field image.

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