Archive for January 2010
Hold still, now, this will take a while:
When J. K. Rowling described Harry Potter’s invisibility cloak as “fluid and silvery”, she probably wasn’t thinking specifically about silver-plated nanoparticles suspended in water. But a team of theorists believe that using such a set-up would make the first soft, tunable metamaterial the “active ingredient” in an invisibility device.
The fluid proposed by Ji-Ping Huang of Fudan University in Shanghai, China, and colleagues, contains magnetite balls 10 nanometres in diameter, coated with a 5-nanometre-thick layer of silver, possibly with polymer chains attached to keep them from clumping.
The chains and columns would lie along the direction of [a] magnetic field. If they were oriented vertically in a pool of water, light striking the surface would refract negatively bent in way that no natural material can manage.
The trick, so far, has been widening the spectrum within which the metamaterials can function: while they’ve successfully blocked infrared in similar experiments, they’re a long way from blocking the complete range of visible wavelengths.
This ruling plugs a loophole in existing law, which forbids the display of humans and animals, live or animated, in such advertising; even having the characters offstage is forbidden.