Making Objects Invisible to Magnetic Fields

After a bit of math wizardry, making the device appear was deceptively simple

2 min read
Making Objects Invisible to Magnetic Fields


Researchers have been trying for years to figure out how to pull a fast one: move an object through an electromagnetic field without disturbing the magnetic field lines. But all their efforts have fallen short.

Today, a team of engineers and physicists at the Slovak Academy of Sciences and Universitat Autònoma de Barcelona reported in Science that they have cracked the code. They say they have created a magnetic cloak that makes objects inside of it invisible to static dc magnetic fields such as the ones in magnetic resonance imaging machines in hospitals and security checkpoints at building entrances.

How did they make the breakthrough when countless other teams’ experimental demonstrations were studies in compromise—with some reflection and shadowing, effectiveness limited to narrow frequency bands, and only partial elimination of field scattering effects? The long and the short of it is that they were diligent math students (Which answers the question of whether math is still relevant). The Spanish and Slovakian researchers first figured out theoretically, “directly from Maxwell equations, that a specially designed cylindrical superconductor-ferromagnetic bilayer” could act as a cloak against uniform static magnetic fields. With their math homework (and perhaps a gold star) in hand, they set about producing just such a cylinder.

They knew what to do to generate just the right amount of repulsion from the inner superconducting layer, and attraction to the outer ferromagnetic one. As it turns out, making the device required little more than a few turns of a commercially available high-temperature superconductor tape wrapped in a few turns of a thick iron-nickel-chromium commercial alloy sheet.

When placed in a magnetic field with a field strength of 40 milliteslas (between two racetrack magnets, as shown in the photo above and in this video), the cylinder left the field lines practically undisturbed. The researchers attributed the slight deviations from their calculations to the possibility that the cylinder’s length-to-diameter ratio was too small and to the fact that they used off-the-shelf materials for the superconducting and ferromagnetic layers. 

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Restoring Hearing With Beams of Light

Gene therapy and optoelectronics could radically upgrade hearing for millions of people

13 min read
A computer graphic shows a gray structure that’s curled like a snail’s shell. A big purple line runs through it. Many clusters of smaller red lines are scattered throughout the curled structure.

Human hearing depends on the cochlea, a snail-shaped structure in the inner ear. A new kind of cochlear implant for people with disabling hearing loss would use beams of light to stimulate the cochlear nerve.

Lakshay Khurana and Daniel Keppeler

There’s a popular misconception that cochlear implants restore natural hearing. In fact, these marvels of engineering give people a new kind of “electric hearing” that they must learn how to use.

Natural hearing results from vibrations hitting tiny structures called hair cells within the cochlea in the inner ear. A cochlear implant bypasses the damaged or dysfunctional parts of the ear and uses electrodes to directly stimulate the cochlear nerve, which sends signals to the brain. When my hearing-impaired patients have their cochlear implants turned on for the first time, they often report that voices sound flat and robotic and that background noises blur together and drown out voices. Although users can have many sessions with technicians to “tune” and adjust their implants’ settings to make sounds more pleasant and helpful, there’s a limit to what can be achieved with today’s technology.

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