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BU Bridge Logo

11 Dec. 1998 - 7 Jan. 1999

Vol. II, No. 17

Feature Article

MET prof's fractal antenna finds a strong reception

By Eric McHenry

When Nathan Cohen first submitted a paper documenting his fractal antenna research to a scholarly journal, the editors thought it was a practical joke.

"I submitted it in February of 1994, to be considered for the April issue of a technical magazine," says Cohen, assistant professor of applied science and director of science and engineering at MET. "They thought it was an April Fool's joke!"

Nathan Cohen

Nathan Cohen, inventor of the compact and highly sensitive fractal antenna (see photo below). Cohen photo by Fred Sway

Although time and continued research have vindicated Cohen, he hasn't forgotten the episode. "I'm not used to being pegged a charlatan," he says. Not long ago, editors of the same journal came to him in hopes of soliciting an article. He'd be happy to write one, he told them, just as soon as they apologized for calling him a prankster. He has yet to receive that apology, and the journal has yet to receive that article.

The whole exchange is illustrative, Cohen says, of the scientific community's occasional tendency to hector fresh ideas right out of its discourse. Essentially, he had discovered that bending conventional antennas into repeating geometric or "deterministic fractal" shapes helped save space and did not adversely affect reception. It's a very simple idea -- and that simplicity, coupled with the fact that Cohen is a radio astronomer by training, not a fractal mathematician, made the antenna an easy target for expressions of skepticism.

"It seems particularly ironic if you think about what I was really asking people to do: bend a 30-cent piece of wire," he says. "It's not like this is a hard experiment to reproduce."

Indeed, Cohen first conducted it on his own ham radio, which he was trying to operate in an apartment complex with a no-antenna rule. He, too, was something of a skeptic at the time, but that didn't prevent him from giving the fractal a chance.

"I had heard Benoit Mandelbrot, who's really the fractal guru, speaking at a conference in 1987," Cohen recalls. "At that time a lot of people, including me, looked upon fractals as snake oil. They were being used to explain everything. When Mandelbrot put up some of his diagrams at the conference, I thought, Oh, wouldn't it be funny to see if this could work for an antenna. A few months later I tried it at home, and found that I could get equivalent reception and save a lot of space."

The operability of antennas in fractal shapes has continued to be their best argument. Since the April Fool's debacle, Cohen has published several articles about them in respected scientific journals. More, he says, should be forthcoming: together with longtime friend and collaborator Robert Hohlfield, CAS research associate professor of computational science, Cohen has recently shown that the efficacy of fractal antennas has a "firm mathematical foundation in Maxwell's equations." (Maxwell's equations are "the Rosetta stone for how electromagnetic waves such as radio and light are made, transmitted, and received," Cohen explains.)

"We've used Maxwell's equations in a novel way," adds Hohlfield, "together with the principles of fractal geometry and symmetries, to identify a class of antennas with some interesting properties" -- properties that have proven, not surprisingly, to be of interest in spheres far larger than those of fractal mathematicians and radio engineers. Earlier this year, Cohen was named a finalist in Discover magazine's ninth annual Technological Innovation Awards. He has also created a high-tech startup company, Fractal Antenna Systems, Inc., which manufactures small, inexpensive antennas for cellular phones and other wireless devices. Unlike the somewhat cumbersome wand-style antennas that cellular phones currently carry, a fractal antenna can fit neatly inside the handset.

"We've just signed a joint-product agreement with a company that makes antennas for cell-phone manufacturers," Cohen says. "In the spring it will be possible to buy cell-phones that use fractal antenna technology."

In addition to making him an entrepreneur, Cohen says, the fractal antenna has made him a student once again. Understanding the subtleties of his discovery has required him to get better acquainted with electromagnetics, a discipline that is not his specialty.

"My background is in radio astronomy," he says, "and I would say my understanding of electromagnetics is modest-to-good, because it's not principally my field. So I've really had to bootstrap my way up. The fractal antenna was really a fantastic invitation for me to become my own grad student."

Ultimately, he says, he'd like to make the interdisciplinary education he's undertaken part of the BU curriculum. The University is already a hotbed for the study of fractal mathematics and fractal physics, he points out. "My aspiration is to start a center for fractal engineering at BU. I think there are so many ways in which engineering can benefit from the study of fractals," he says.

Visit the Fractal Antenna Systems, Inc., Web site at www.fractenna.com.