Someone should call the physics police. A new class of composite materials reverses the behavior of many fundamental electromagnetic properties. During a recent experiment at the University of California in San Diego, electromagnetic radiation travelled through this material in a manner never before seen in nature.
The composite is fabricated from fiberglass and copper. Termed a "metamaterial," it's composed of repeating elements. Essentially, it consists of a series of thin fiberglass sheets coated with copper rings and wires and arranged into squares (see the figure).
When microwaves pass through the material, they bend in a direction opposite to that predicted by the laws of physics. In contrast, when electromagnetic radiation in the form of light or microwaves passes through an ordinary material, the waves are deflected in the same direction. This behavior generates a positive index of refraction.
The larger a material's index of refraction, the slower light travels through the material. Also, a larger index means that light "bends" or changes direction more when going from one material to another. Researchers are describing the UCSD composite as the first material to possess a "negative index of refraction."
Initially, the UCSD scientists created a handheld-sized sample of the material. Then, they fired microwaves at police-radar frequencies through the sample. As the scientists predicted, the microwaves emerged from the sample in a direction opposite to that predicted by Snell's Law (which describes the angle of refraction produced by the slowing of light and other forms of electromagnetic radiation through water, glass, and other materials).
The scientists are currently examining the possibility of similar behavior at optical frequencies. According to the team, this property would generate behavior whereby a small flashlight focused on a flat sheet of the material would produce a focus at a point on the other side. This behavior is unknown in ordinary composite materials.
UCSD physicists Sheldon Schultz, David R. Smith, and Richard A. Shelby believe they have created a new class of materials that reverses the "right-hand rules" of physics. These rules define the relationships between electric and magnetic fields and the direction of their wave velocity.
The team also predicts that the composite will reverse the Doppler effect. Based on Maxwell's Equations, which establish the relationship between magnetic and electric fields, microwave radiation or light from a moving source will shift to lower frequencies as a source approaches the composite and to higher frequencies as it recedes from an observer.
Currently, the composite cannot focus visible light. Yet the scientists believe this obstacle may be eliminated in future negative refractive-index materials. They also say the composite may prove useful in developing novel antennas and other electromagnetic materials for cellular communications.
It additionally may enable the construction of a "perfect lens," one capable of focusing light and other forms of radiation to limits beyond those of normal lenses. A lens manufactured from the UCSD material would not be limited by a diffraction limit. A diffraction limit prevents a standard lens from focusing light that enters its surface into a spot smaller than about half a wavelength in diameter.
The researchers have filed a patent application covering the construction of the new composite material. The Defense Advanced Research Projects Agency and the Air Force Office for Science Research, both supporters of the experiment, are investigating potential applications. For more information, go to www.ucsdnews.ucsd.edu.