August 2004 
Volume 03, Issue 4 
Tech Talk

Bending microwaves the ‘wrong’ way


cube with embedded copper loops and ringsBoeing research scientists, working with physicists at the University of California–San Diego and other universities under a Defense Advanced Research Projects Agency contract, have been demonstrating something new about the law of refraction, one of the oldest of the laws of physics.

The team’s discoveries involve the fabrication of a new class of artificial materials called “metamaterials” that bend electromagnetic waves in a manner not seen in nature. Such a capability could someday prove useful in the development of significantly smaller, more-powerful and lower-cost antennas and other electromagnetic devices, and could also lead to the development of improved lenses capable of focusing light and other forms of radiation to limits not achievable by normal lenses.

Science magazine cited these discoveries earlier this year in its list of the top 10 science breakthroughs of 2003. And the June 2004 edition of Physics Today magazine, the flagship publication of the American Institute of Physics, showcased a photo of a Boeing-built metamaterial sample on its cover.

“We have been learning a lot more about the novel properties of electromagnetic metamaterials,” said Minas Tanielian, manager of Microsystems and Electronics Technology in Boeing Phantom Works. “Although this technology is still in its infancy, it is clear that it could have a tremendous effect on many aerospace products.”

Phantom Works employees at the Microsystems  and Electronics Technology Lab In its work under the $5.6 million DARPA contract, the Boeing-led team has been engineering and fabricating metamaterials to gain a better understanding of the physics of electromagnetic materials, particularly those that demonstrate a “negative index of refraction.” Materials found in nature always bend electromagnetic waves in the same direction, giving those materials a “positive index of refraction.”

“Our objectives have been to improve existing tools for modeling and simulating more complicated patterns and lattices in the metamaterials, to fabricate the materials using various materials and processes, to test the electromagnetic behavior of the metamaterials in the laboratory and in aerospace environments, and to identify applications where such materials can make a big difference,” Tanielian said.

How it works

If you’ve ever wondered why a drinking straw appears to bend at the point it enters water in a glass, then you’ve thought about the law of refraction, first derived by Willibrord Snell in 1621. The Dutch physicist was the author of Snell’s Law, which describes the angle of refraction produced by the slowing of light through water, glass and other ordinary material.

Physicists measure the bending of light, microwaves and other forms of electromagnetic radiation through a material by its “index of refraction.” The bigger a material’s index, the slower light travels through it, and the more it “bends,” or changes direction when going from one material to another. As it interacts with the atoms and molecules in materials found in nature, electromagnetic radiation always is deflected in the same direction, giving those materials a “positive index of refraction.”

However, in 1968, a Soviet physicist named Victor Veselago hypothesized that a material with a negative index of refraction, or “left-handed material,” could possibly exist, without violating any of the laws of physics. In 2000, physicists at the University of California in San Diego, building on work done at the Imperial College in London and other research, used a combination of copper rings and wires etched on a circuit board to create an experimental metamaterial that confirmed a microwave beam would undergo negative refraction at the interface between the metamaterial and air—unlike any existing material.

Since then, the Boeing-led team, using sophisticated microfabrication and simulation techniques, has produced three-dimensional lattices of copper loops and rings embedded in a nonconducting material that create an electromagnetic field that deflects light in the opposite direction of natural materials. In the process, they have learned a great deal about the curious behavior, and potential possibilities, of these left-handed materials.

“Through this promising research, we are able to explore new frontiers in optical and electromagnetic effects that could yield much higher-performance and lower-cost communications, surveillance and computer systems in the future,” said Minas Tanelian of Boeing Phantom Works.




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