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How To Build An Antimagnet

A cloak that hides magnets from the outside world could have remarkable applications, say physicists

A metamaterial is a bizarre substance with properties that physicists can fine tune as they wish. Tuned in a certain way, a metamaterial can make light perform all kinds of gymnastics, steering it round objects to make them seem invisible.

This phenomenon, known as cloaking, is set to revolutionise various areas of electromagnetic science.

But metamaterials can do more. One idea is that as well as electromagnetic fields, metamaterials ought to be able to manipulate plain old magnetic fields too. After all, a static magnetic field is merely an electromagnetic wave with a frequency of zero.

So creating a magnetic invisibility cloak isn’t such a crazy idea.

Today, Alvaro Sanchez and friends at Universitat Autonoma de Barcelona in Spain reveal the design of a cloak that can do just this.

The basic ingredients are two materials; one with a permeability that is smaller than 1 in one direction and one with a permeability greater than one in a perpendicular direction.

Materials with these permeabilities are easy to find. Superconductors have a permeability of 0 and ordinary ferromagnets have a permeability greater than 1.

The difficulty is creating a material with both these properties at the same time. Sanchez and co solve the problem with a design consisting of ferromagnetic shells coated with a superconducting layer.

The result is a device that can completely shield the outside world from a magnet inside it.

That could be a useful toy. As it becomes superconducting, such a device would suddenly become opaque to a magnetic field inside it. To an observer, it would be as if the magnet had been switched off.

Sanchez and co call their device an ‘antimagnet’ and say it could have some interesting applications: “Antimagnet devices may bring important advantages in fifields like reducing the magnetic signature of vessels or in allowing patients with pacemakers or cochlear implants to use medical equipment based on magnetic fifields, such as magnetic resonance imaging or transcraneal magnetic stimulation.”

All they have to do now is build one.

Ref: arxiv.org/abs/1107.1647: Antimagnets: Controlling Magnetic fiFields With Superconductor-Metamaterial Hybrids

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