Researchers develop magnetic cloak using standard materials

The ‘magnetic cloak’ could be used to protect implanted medical devices such as pacemakers and cochlear implants — although it might also potentially be used surreptitiously to hide metallic weapons from security portals.

Previous attempts at creating cloaking technology have focused on developing entirely new metamaterials that have underlying properties not found in normal matter.

‘Metamaterials are very costly to manufacture since they are often complex, fine-tuned structures,’ Prof Àlvar Sánchez of the Autonomous University of Barcelona (UAB) told The Engineer. ‘The challenge we posed ourselves was to design a cloak that yielded complete, not reduced, invisibility and made from commercially available materials.’

Their device is a cylinder built using a high-temperature superconductor material, easily refrigerated with liquid nitrogen and covered in a layer of iron, nickel and chrome.

‘To come up with the final engineering-like solution, we needed to work a lot with the physics and mathematics of transformation optics,’ Sánchez said.

The superconductor layer of the cylinder prevents the magnetic field from reaching the interior, but distorts the external field and thus makes it detectable.

To avoid detection, the ferromagnetic outer layer, made of iron, nickel and chrome, produces the opposite effect.

It attracts the magnetic field lines and compensates the distortion created by the superconductor, but without allowing the field to reach the interior.

The global effect is a completely non-existent magnetic field inside the cylinder and absolutely no distortions in the magnetic field outside.

Given that magnetic fields are so widely used in the technology — in energy generation, motors, magnetic memory and medical equipment — Sánchez believes the team’s ideas could find use in many applications requiring the shielding of a magnetic field without external field distortion.

‘In other proposals for cloaking electromagnetic waves at some non-zero frequency, the size of the objects was limited by the wavelength — here the wavelength static fields can be regarded as infinite, so any size could be considered,’ he said.