How to Make a Liquid Invisibility Cloak
Photo via flickr by all-i-oli
If researchers at Fudan University in Shanghai are right, we may all someday possess Harry Potter’s invisibility cloak. The theorists believe that silver-plated nanoparticles suspended in water and aligned in a magnetic field could allow for creating a metamaterial—the “active ingredient” in an invisibility device.
The fluid proposed by Ji-Ping Huang and colleagues of Fudan University 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.
In the absence of a magnetic field, such nanoparticles would simply float around in the water, but if a field were introduced, the particles would self-assemble into chains whose lengths depend on the strength of the field, and which can also attract one another to form thicker columns.
The chains and columns would lie along the direction of the magnetic field. If they were oriented vertically in a pool of water, light striking the surface would refract negatively—bent in a way that no natural material can manage.
This property could be exploited for invisibility devices, directing light around an object so that it appears as if nothing is there, or be put to use in lenses that could capture finer details than any optical microscope.
This isn’t the first attempt at building an invisibility device. David Smith and his team at Duke University in September 2006 had built a device that could hide an object from view, but only from the “eyes” of a microwave detector—and then only at a very specific microwave frequency.