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Posted: Jan 20, 2011

Fractals Offer New Way to Be Cool

(Nanowerk News) Fractal Antenna Systems, Inc., a Boston area firm, today disclosed patent filing for a breakthrough technology in heat transfer and dissipation. Heat transfer is a basic and key technology for making things work and work better, from computers to video game consoles to refrigerators, by taking heat away from where it is not wanted or selectively placing it where it is needed.
The technology uses fractal shapes, a complex pattern built up from repeated and scaled repetitions of a simpler one, to make infrared (IR) resonators that are broadband. Infrared is the part of the spectrum where heat gives off most of its energy and has the same properties as microwave, except at shorter wavelengths.
By juxtaposing the fractal resonators very close to one another in a layered grid, they generate "surface" waves that can transfer IR energy. This fractal "metasurface" metamaterial thus can take heat away from one spot, and almost instantaneously, transfer the energy elsewhere.
Methods for transferring heat have been known for decades, and include: radiation, evaporation, phase transitions, conductivity, convective, thermoelectric, and more. The new "metasurface" heat transfer method is unique and different. Although related to conventional radiative transfer, it exploits coupling of surface waves and thus can be easily directed whereas radiative transfer is not. It is also totally passive, requiring no power.
The use of fractals is key to the practical realization of "metasurface" heat transfer, as their use allows the resonators to best couple to each other, over a broad infrared band, where most of the heat radiates. Other resonators used have not demonstrated this advantage. And in a unique advantage, broadband use of the fractals does not require that they be microns in size, thereby making it possible to fabricate them with a greater range of possible techniques.
"It is now possible, although not yet practical, to transfer heat in a way analogous to how we transfer electric current on a wire, without the delays inherent to heat capacities and cooling rates," noted the firm's CEO Nathan Cohen. "This fascinating application of fractals fell out from experimenting with the wideband invisibility cloak we invented three years ago."
The firm's wideband invisibility cloak, shown aabove, slipstreams microwaves around an obstacle to the opposite side, thereby making the obstacle imperceptible. Using ducting properties from the fractal metamaterial surface waves, it became clear to researchers of the firm that other applications could be enabled by the research, unrelated to cloaking.
"It is natural to extrapolate the findings done at microwave to infrared. In fact it is much easier to prove out ideas at microwave, which we continue to do," said Cohen.
Cohen notes that infrared development for efficient fractal "metasurface" heat transfer is likely to be 2 to 5 years away. "The speed at which we see this new technology proven out in real applications ultimately is determined by who needs it, and who needs it now." Cohen noted that material properties will require the most development and will determine when the new "metasurface" heat transfer technology will become more ubiquitous, such as an enhancement or replacement of heat sinks in electronics.
About Fractal Antenna Systems, Inc.
Fractal Antenna Systems, Inc. (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 (press release)
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