have been a mathematical curiosity since first being popularized by
Benoit Mandelbrot(who coined the term) in the 1960s. Perhaps, and in retrospect no coincidence, was
the popularity of the cloaking concept featured in the 1960s phenomenon called
Star Trek. I say coincidence because who
would have guessed that some of the leading research in invisibility cloaking would involve barriers derived from
fractal forms? Have aliens been guiding the technology? If so, maybe they're working at Fractal Antenna Systems,
because in mid December the company issued a
detailing work being done on a cloaking system that works in the microwave band (as opposed
to visible light) - chosen for convenience of size. Results are quite impressive as can be seen in the
I am not totally convinced that fractals are a necessary part of cloaking, but they do make for interesting
publicity photos. After all, if fractals are part of the cloaking equation, then wouldn't fractal-shapes in nature
like coastlines and foliage help make them invisible to something noticeable - sound, light, and/or water waves?
The magic is probably in the increased projected surface area generated by a fractal's stepped outline. A
multitude of similarly dimensioned curved surfaces might actually be better, but curves are broken down into
polygons for computer modeling, so that still leaves you analyzing multifaceted flat surfaces.
(Waltham, MA--21 Dec 2010) Can you see it? Researchers at Fractal Antenna Systems have written a new
chapter in the science of making things disappears. Their wideband microwave invisibility cloak, first revealed in
March 2009, now makes its debut for everyone to see in a new video:
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.
Holy Grail of
Cloak Design 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.
The firm's cloak also marks the steady and remarkable
process of innovation afforded by fractals in antennas and electronics. Oddly, many American antenna researchers
have shied away from fractal design, while interest in Asia and Europe bloomed, noted Cohen. However, as recently
shown on PBS's NOVA television program, fractals have a great impact on antennas and electronics, and researchers
from all continents except Antarctica now boast many dozens of active research programs.
believes that success in cloaking science requires a body of diverse knowledge, which in his case drew upon
experience as an astronomer, and curiously, as a radio ham operator. "I have a Ph.D. in astrophysics and am a
retired college professor. But the experience I gained as a young ham radio operator was invaluable in helping me
make knowledge connections to make the cloak work. That's, in part, why my research group did this first, and why
we continue to lead in innovation in fractal electronics, both in basic research and application to products."
Fractal Antenna Systems, Inc. Fractal Antenna Systems, Inc. (http://www.fractenna.com)
supplies products for the world's most demanding wireless, and electromagnetic applications. Backed by over three
dozen U.S., and international patents, plus dozens of patents pending, Fractal Antenna Systems is the recognized
pioneer in fractal technology, with extensive research and field experience over 15 years in business. The company
is a privately held and headquartered in Waltham, Massachusetts, USA. SOURCE: Fractal Antenna Systems,Inc.
These items are an archive of past Topical Smorgasbord items that have appeared on the RF Cafe homepage. In keeping with the "cafe"
genre, these tidbits of information are truly a smorgasbord of topics. They all pertain to topics that are related to the general engineering
and science theme of RF Cafe. Note: There is also a huge collection of my 'Factoids' (aka 'Kirt's Cogitations') that might interest you as well.