Tag Archives: invisibility cloak

Hiding a peppercorn with your invisibility cloak

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It’s the first time I’ve heard of an invisibility cloak that can hide something visible to the naked eye.  A peppercorn may not sound like much but compared to cloaked objects that are usually measured at the nanoscale (nano means one billionth of a metre), this is a huge step forward. What makes this discovery even more interesting is that it’s simple and inexpensive compared to the other systems used to achieve invisibility. From the Jan. 25, 2011 news item on Nanowerk,

Unlike the other attempts to produce invisibility by constructing synthetic layered materials, the new method uses an ordinary, common mineral called calcite — a crystalline form of calcium carbonate, the main ingredient in seashells. “Very often, the obvious solution is just sitting there,” says MIT mechanical-engineering professor George Barbastathis, one of the new report’s co-authors.

The work is being done by a team of researchers from the Singapore-MIT Alliance for Research & Technology (SMART). From the SMART website,

Established in 2007, the SMART Centre is MIT’s first research centre outside of Cambridge, MA and its largest international research endeavor. The Centre is also the first entity in the Campus for Research Excellence and Technological Enterprise (CREATE) currently being developed by NRF.

Here’s how they created an invisibility cloak,

In the experiment reported in this paper, the system works in a very carefully controlled setting: The object to be hidden (a metal wedge in the experiment, or anything smaller than it) is placed on a flat, horizontal mirror, and a layer of calcite crystal — made up of two pieces with opposite crystal orientations, glued together — is placed on top of it. When illuminated by visible light and viewed from a certain direction, the object under the calcite layer “disappears,” and the observer sees the scene as if there was nothing at all on top of the mirror.

The latest invisibility cloak

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Fractal Antenna Systems Inc. has released a video which demonstrates an invisibility cloak. From the Dec. 20, 2010 news item on Nanowerk,

The video conclusively shows that invisibility science has taken a huge leap with fractal design. Fractals are geometric patterns that have complex structure built from scaled repetition of a simple pattern. Fractals make up the cloak and its ‘object’ layer, producing a wideband invisibility that slipstreams microwaves around obstacles. The other side appears with good fidelity, without the detectable presence of the obstacle. Although a proof-of-concept of an invisibility cloak was shown in 2006 at Duke University, such non-fractal efforts had limitations. The Duke cloak worked in one narrow band, had many more cloaking layers, possessed a discernable shadow, and required the obstacle to already be hiding behind a mirror. All of those obstacles have been solved using fractals, in grids called fractal metamaterial, as the firm’s cloak reveals.

I located the 2006 video from Duke University,

It’s Fractal Antenna System’s ability to project a wideband invisibility cloak that distinguishes this effort from Duke’s (from the news item),

Notes the firm’s CEO and chief inventor Nathan Cohen: “In 2008, Chinese researchers said it was impossible to make a wideband invisibility cloak. We not only did it, but reduced the number of cloak layers, and, most importantly, made a cloak you can see out of. That means a sensor, for example, can be made to disappear into the background over a wideband, but still be able to see what’s outside. These attributes are really the ‘holy grail’ of cloak designs, and strongly point towards a bright future for invisibility science.”

The fractal cloak works at microwaves; radio waves used by cell phones and wireless devices. The technology directly applies to infrared, and with technology advances in nanotechnology, can be made to make visual light invisibility cloaks, although Cohen cautions that it will be many years before visual light invisibility cloaks are perfected. “Other researchers are still hiding objects behind mirrors. What’s the point of a cloak if you are already hiding behind a mirror?” asked Cohen.

As best as I can tell, the objects that are being cloaked are not visible to the human eye as they are measurable at the nanoscale. Here’s the Fractal Antenna Systems video (from YouTube),

The narrator seems to have some an unfortunate vocal habit, he overmodulates so some parts are a bit ‘sing-song’.