Cloaking device

A device that can block magnetic fields using metamaterials has been modelled by a team in Spain, according to a study released Friday, which could be used in a variety of medical and security contexts.

In the study, published in the Institute of Physics and German Physical Society's New Journal of Physics, researchers from the Universitat Autonoma de Barcelona presented their computer model that both prevents magnetism from leading out of a containment device or which shields it from external magnetic fields.

The scientists said such a cloak, which they call an "antimagnet," could be built using practical and available materials and technologies and developed for use in a variety of applications.

One use could be with patients who have pacemakers or cochlear implants. Because those devices are sensitive to MRI scanners or other magnetism-based equipment, often people cannot be tested with them. A magnet cloak could solve that problem.

Another potential application could be protecting a ship's hull from mines that are designed to explode when they encounter a magnetic field.

Metamaterials

The design consists of several layers of metamaterials, or materials not found in nature which are created with specific electromagnetic properties, for example with extremely tiny holes or coils that perform certain functions.

One layer of the cloak would consist of a superconducting material that would stop a magnetic field from leaking outside. However, that would distort the magnetic field placed over the cloak, thereby making it detectable.

Therefore, the device would have to have several additional metamaterial layers that would correct the distortion.

"The function of the superconducting metamaterial layers is to guide, jointly with other homogeneous magnetic layers, the magnetic field lines through the antimagnet in order to keep the exterior magnetic field undisturbed," Alvar Sanchez, the lead author on the story, told Deutsche Welle.

In the paper, the team used computer simulations of a ten-layered cylindrical device that cloaked a single small magnet.

However, they believe that in the real world, devices could be built in almost any geometric shape. Alvar said that even an antimagnet that was not fully closed would have good cloaking properties.

Building on previous finds

The findings of the Spanish team are built on research by John Pendry and his team at Imperial College London. In 2008, he and his colleagues also proposed a cloaking device using a combination of materials that had limited permeability, but their research did not move past the computer modelling phase.

"The Spanish group has come up with a new design for the metamaterials which builds on what he have done," Pendry, who was not part of the new research team, told Deutsche Welle. "They claim it is a much more realistic possibility than what we proposed."

He said the difficulty lies in the creation of the extremely complicated metamaterials, which require substances be cooled down to extremely low temperatures. If the computer model demands using a material that is too complex, he said, it can be very difficult to make.

"The simpler the theorist can make it, the more likely his ideas will be picked up by experimenters," he added. "That's what the Spanish group has done."

Alvar said his team has been in contact with other researchers about building a simple model of the antimagnet and they hope to start working on a prototype in the near future.

Security downside

One downside to the technology, however, is that is could enable criminals to get by security systems in airports and buildings, which machines might not be able to detect metal objects hidden behind the cloak.

That could mean that security officials would have to design new types of detection systems.

However, Alvar said that is probably fairly far off in the future. The proposed antimagnet needs cryogenics because of the superconducting materials, putting it out of reach for most criminals.

Probably, he added, it would only work initially for quite small magnetic fields.

"It's probably not yet time to design new detection system because of the antimagnet, but maybe it should be taken into account in not-so-distant future," he said.

Author: Kyle James

Editor: Cyrus Farivar