Thursday, September 23, 2004

"METAMATERIAL: Lens focuses sound, not light"
Metamaterials reverse the ordinary laws of nature, such as Snell's "right-hand" law for electromagnetism, which states that magnetism curls in the same direction in which the fingers of your right hand curl around a wire when you point with your thumb in the direction of current flow. By 2003, researchers had verified that not only were these engineered materials possible, but they also could enable "perfect" lenses that were nevertheless flat. Now metamaterials are being demonstrated not just for electromagnetic waves, but for anything that can be described by wave functions, thereby reversing the laws of nature for acoustic engineering, ultrasound, microwaves, light and magnetism. "What we have is a larger version, structurally, of a photonic crystal, adjusted for the wavelength of ultrasound," said John Page, a professor at the University of Manitoba in Winnipeg. "Our metamaterials use artificial atoms arranged in a lattice that filters acoustic wavelengths the way that photonic crystals filter optical wavelengths." Metamaterials substitute macroscopic objects for atoms in a giant crystalline lattice-here made from tungsten carbide beads surrounded by water and packed flat into planes, with a spacing between beads set to a subwavelength of the wavelength you want to affect.