Coming soon: Knavish electromagnetic acts

It could be a new sequel to Alice in Wonderland. Only in this story, the protagonist finds that ordinary optics become wildly unfamiliar. Looking glasses turn oddly opaque, for instance, and convex lenses spread rather than focus light.

Refraction disperses rays (above) from a point source that hit a slab (between red lines) of ordinary transparent material. An odd, new material (below) is expected to refocus electromagnetic radiation. Rick Shelby/UCSD

Rick Shelby/UCSD

Setting the scene for that sequel is a team of California scientists who have created a new type of device with bizarre electromagnetic properties. Their invention exhibits its queer traits only at microwave frequencies, but versions that function at the much higher frequencies of visible light might become possible, the scientists say.

Unlike Alice, who found that things were getting “curiouser and curiouser,” Sheldon Schultz of the University of California, San Diego (UCSD) says he and his team expect to find them becoming “reverser and reverser.”

Within the device, radiation will act contrary to the way it does in ordinary materials, the scientists predict. For example, the Doppler effect should reverse, so that radiation bouncing off an approaching object would decrease rather than increase in frequency. Moreover, pressure ordinarily exerted by electromagnetic radiation should become an attractive force. The researchers say they plan to conduct experiments soon to verify these and other peculiar behaviors.

Schultz and David R. Smith, who together led the UCSD team, unveiled their creation March 21 in Minneapolis at a meeting of the American Physical Society. “It’s really clever work,” comments physicist Douglas L. Mills of the University of California, Irvine. “They are to be congratulated for a very great step forward,” says John B. Pendry of Imperial College in London. Research by Pendry and his colleagues laid groundwork for the new development.

To make their device, Schultz, Smith, and their colleagues electroplated C-shaped copper rings onto a strip of backing, one row per strip. They then wedged these strips between upper and lower aluminum plates. The researchers also stood rows of copper rods, each connecting the top and bottom plates, in the 1-centimeter-wide spaces between the strips. The structure requires no power.

Although made from discrete components, the new device influences electromagnetic waves as if it were a continuous material, the researchers say. That’s because the spacing between components is small compared with the wavelengths of microwaves, they explain.

For any material, two properties known as permittivity and permeability determine how it responds to electric and magnetic fields, respectively. If either property takes on a negative value, something unusual is going on.

In computer simulations and experiments, the researchers found that within a narrow band of microwave frequencies, both the permittivity and permeability of their device were negative. That condition had never been seen before in any material or device, although negative permittivity alone has been observed, the researchers say. A Soviet physicist in the late 1960s predicted many strange effects in a hypothetical material with negative values of both properties.

Schultz and Smith say that their innovation promises to lead to new types of microwave components, such as oscillators, antennae, and delay lines. That’s important, Pendry says, because “the range of materials for controlling microwaves is very limited.”

To make a visible-light version of the device, researchers would have to fabricate components on the scale of nanometers instead of centimeters—a much tougher challenge. Schultz predicts, nonetheless, that such a material’s strangeness and possible usefulness will spark a mad dash among researchers to build it.

Will they be like Alices chasing after an ever-elusive rabbit? Mills and Schultz both say that infrared versions seem possible, but visible-frequency ones are more iffy. Says Schultz, “The race to higher frequency has begun!”

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