By Andrew Nusca
Posting in Energy
A team of scientists believe that silver-plated nanoparticles suspended in water could help make a real-life invisibility cloak.
A team led by Ji-Ping Huang of Fudan University in Shanghai, China has developed a fluid that contains magnetite balls 10 nanometers in diameter, coated with a 5-nanometer-thick layer of silver with polymer chains to help discourage clumping, reports the New Scientist.
With the introduction of a magnetic field, the nanoparticles self-assemble into chains positioned along the direction of the magnetic field, with lengths and widths that correspond to the strength of the field.
Oriented vertically in a pool of water, light that strikes the surface would refract negatively -- bent in a way that no natural material can manage.
That would theoretically make the team's fluid the first pliable metamaterial, a core ingredient in an invisibility cloak.
An invisibility cloak works by directing light around an object so that it appears as if nothing is there. The technology could also be used in lenses to capture finer details than an optical microscope.
A solid metamaterial that negatively refracts the long wavelengths of red light has already been developed. For now, the Fudan team has only simulated three wavelengths to confirm negative refraction for the red portion of the visible spectrum into infrared wavelengths -- meaning a liquid invisibility cloak that refracts all visible light is theoretically sound on paper, but not yet in practice.
The question is whether the researchers can extend their technique to the rest of the visible light spectrum in practice. If any light is absorbed or redirected, "dark spots" would result.
Why so difficult? The smaller the wavelengths of light, the smaller the structures needed to control them must be, which in turn are progressively more difficult to build.
Jan 11, 2010