A Negative Index of Refraction

Has been generated in a specially engineered structure. An electromagnetic wave in air that is incident on a conventional medium with a positive index (such as glass or water) will be refracted toward the normal, with an angle given by Snell’s Law. With a negative-index medium, Snell’s Law still applies, but with a peculiar result: The wave will be refracted at a negative angle—it never crosses the normal. In the recent experiment, David Smith, Sheldon Schultz, and Richard Shelby (all at the University of California, San Diego) found that a beam of microwaves entering the special structure came out on the “wrong” side of the normal, confirming the negative index. As shown here, the structure is a two-dimensional array of copper split-ring resonators and wires mounted on fiberglass boards. Last year, the UCSD team showed that a similar “metamaterial” has negative values of both the electrical permittivity ε and the...