'Left-handed' material reverses Doppler effect

17 Jun 2002

Physicists at the University of California, San Diego have developed a material that, at microwave frequencies, reverses Doppler shift, Snell's law and the direction in which Cerenkov radiation is emitted.
Sheldon Schultz and David Smith, who call the material 'left-handed', believe that it will have applications in wireless communication. They now hope to extend the effect into the infrared and visible regions.

According to Smith, the key to the work lies in the split ring resonators - structures composed of copper rings and wires - developed by John Pendry at Imperial College, London. The rings have a negative magnetic permeability, while the wires exhibit negative electric permittivity. In combination, these effects reverse wave propagation in the material, so that it appears to travel in a direction opposite to that of the energy. A stationary observer would see red-shifted emission from a source moving towards them, and blue-shifted when moving away. Light passing from a 'normal' to a 'left-handed' medium would be refracted towards the opposite side of the normal - a reversal of Snell's law of refraction.

Smith and Schultz will now investigate other materials for similar properties, hoping to extend the frequency range where the effects are seen into the infrared and visible regions. "There is no problem making the resonators at infrared and optical wavelengths with lithography. The question will be whether or not the magnetic properties that we ascribe to the resonators scale up to higher frequencies," said Smith.
The effects shown by a material with negative permeability were predicted by Russian physicist Victor Veselago in 1968. Up until now, no such materials were known.