16 July 2009

Now you see it, now you don't

Seeing is believing, but not seeing something may also be believable as a new device can make objects invisible under certain light.

By using very low frequency electromagnetic waves, it is possible to make the inside of the magnetic field zero while not altering the exterior field. The device, which up until now has worked in theory, can act as an invisibility cloak, making the object completely undetectable to these waves.

“The theoretical work provides the details for constructing a real dc metamaterial and represents another step towards invisibility,” said Àlvar Sánchez, director of the research in the Department of Physics at the Universitat Autònoma de Barcelona (UAB). “Now comes a very important stage: Building a prototype in the laboratory and applying this device to improving magnetic field detection technology.”

Technically, any object could be invisible if covered with something that could make the light surround it, instead of absorbing or reflecting it. Thus, it would be impossible to see the object since the light would only pass around it, and if one were to look directly at the object, one would only see what is behind it. The object would become imperceptible.

Until recently, scientists believed this type of “invisibility cloak” would be impossible to create, given that the trajectory of light in a specific environment is the end result of the medium electric and magnetic properties, with values scientists thought they could not modify and therefore made invisibility impossible. However, more recent scientific discoveries show they can modify these values with the help of artificial materials containing unusual physical properties: Metamaterials. These materials have unique electric and magnetic properties which, at least theoretically, could affect light in a way they would make light pass around an object, and thus make it invisible.

Invisibility in visible light, the rainbow-color spectrum we can see with our own eyes, has not yet occurred with experiments. Nonetheless, scientists are working with other types of light such as microwaves, low frequency electromagnetic fields (such as radio or television waves), or even with constant magnetic fields such as magnets or the Earth’s magnetic field.

The metamaterial designed by the research group at UAB consists in an irregular network of superconductors, which give materials specific magnetic properties that can create “invisible” areas in the magnetic field and in very low frequency electromagnetic fields. The discovery can work for medical purposes, such as magnetoencephalographic or magnetocardiographic techniques (used to measure the magnetic fields created by the brain or the heart), which in order to function properly need to shield out all other existing magnetic fields. They also can see use in other areas in which magnetic field detection is important such as in sensors, or to prevent the magnetic detection of ships or submarines.

For related information, go to www.isa.org/manufacturing_automation.