'Left-Handed' Material Puts Twist on Physics

MINNEAPOLIS--Physicists are marveling over a small, fairly simple contraption of wires and copper rings that can reverse the magnetic field in microwaves, seemingly thumbing its nose at a venerated standard of high school physics. The device, presented here Tuesday at the annual March meeting of the American Physical Society, may someday lead to innovations in microwave technology and cellular communications.

Place almost any material in a magnetic field, and an internal magnetic field pointing in the same direction will arise inside it. However, no law of physics prohibits the internal field from pointing in the opposite direction in some material. More than 30 years ago, Russian physicist Victor Veselago speculated about how electromagnetic waves would behave in such a material, should it ever be discovered or created. Now David Smith, Sheldon Schultz, and their co-workers at the University of California (UC), San Diego, have produced one.

Their device consists of a square grid of vertical wires roughly a centimeter long. Between the rows of wires lie metal rings a few millimeters in diameter. When microwaves enter the assembly, their oscillating magnetic fields cause electric currents to slosh back and forth in the rings; at frequencies of roughly 5 gigahertz, the rings resonate to produce a large magnetic field in the opposite direction of the incoming waves. At the same time, a more common phenomenon occurs: The wires reverse the oscillating electric field that is also part of the microwaves.

The twinned reversed fields give rise to some weird phenomena, such as electromagnetic waves that flow in the opposite direction of the energy they carry. This seems to violate the cherished "right-hand rule," which is usually taken to say that if the electric field points to twelve and the magnetic field points to nine on an imaginary clock, then both the wave and the energy it carries flow out of the clock's face. But the new material doesn't really challenge the accepted laws of electricity and magnetism, says UC Berkeley theoretical physicist Marvin Cohen: Strictly speaking, haggard students should use the external magnetic field when figuring the direction of energy flow and the internal magnetic field when figuring the direction of wave propagation, which puts an end to the apparent paradox.

Physicist Costas Soukoulis of the Iowa State University in Ames says he's excited about the potential for these "left-handed" materials. Combined with nanotechnology, he says, they may help produce outlandish devices for visible light such as lenses that focus even though they are flat. But such advances may take time. "It's like looking at a baby and saying, 'What is it good for?'" Cohen says. "It takes a while to develop."