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Author Topic: Innsbruck quantum physicists have constructed a diode for magnetic fields  (Read 403 times)
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First diode for magnetic fields

Luis Veloso
When the left coil is energized, the magnetic field reaches the right coil (top). When the right coil is energized, the magnetic field does not reach the left one (bottom).

Innsbruck quantum physicists have constructed a diode for magnetic fields and then tested it in the laboratory. The device, developed by the research groups led by the theorist Oriol Romero-Isart and the experimental physicist Gerhard Kirchmair, could open up a number of new applications.

Electric diodes are essential electronic components that conduct electricity in one direction but prevent conduction in the opposite one. They are found at the core of any electronic component, being one of the most essential building blocks. Until now there were no such components for magnetic fields. Physicists at the University of Innsbruck and the ÖAW Institute of Quantum Optics and Quantum Information (IQOQI) are now changing that. They designed the first diode for magnetic fields and demonstrated its functionality in the laboratory.

“Our device makes possible to transfer the magnetic field from a first magnetic element - for example a magnet or a coil - to a second one. When roles are inverted and one tries to send magnetic field from the second to the first, no magnetic field is transferred," explains first author Jordi Prat Camps, who is now a researcher at the University of Sussex in England. Technically speaking, this means that the mutual inductances between the two sources, which are routinely assumed to be symmetric, can be made extremely asymmetric. The key element to obtain this result is the use of an electrical conductor that moves with constant velocity. “When the conductor is properly placed near to the magnetic elements and is moved at the right speed, the coupling between them becomes unidirectional, and a diode for magnetic fields is realized”, says Jordi Prat Camps.

Coupled magnetic elements are found in many key technologies like electric motors, transformers, magnetic memories or MRI machines. In all of them, magnetic elements are symmetrically coupled. “The availability of a new magnetic tool like a diode might thus open a bunch of new possibilities”, Gerhard Kirchmair points to the future. For example, the efficiency of wireless charging devices could be improved, since the energy can only flow from the charging station to the device and not in the other direction.

Original publication:

"Circumventing Magnetostatic Reciprocity: a Diode for Magnetic Fields"; J. Prat-Camps, P. Maurer, G. Kirchmair, and O. Romero-Isart; Phys. Rev. Lett.; 121,

end snip
from here http://www.chemeurope.com/en/news/1158513/first-diode-for-magnetic-fields.html

member bistander provided research info here

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contribution from Member F6FLT  at Stefans forum

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Interesting!  makes one wonder whether Lenz' law can be circumvented somehow?

Synopsis: One-Way Transfer of Magnetic Fields
November 20, 2018
Researchers have created a material that acts as a magnetic diode, transferring magnetism from one object to another but not the other way around. 

J. Prat-Camps et al., Phys. Rev. Lett. (2018)

Jordi Prat-Camps creates magnetic metamaterials—structures that manipulate magnetic fields in unconventional ways. Over the last few years, the physicist, who is at the University of Sussex in the UK, and his colleagues have constructed a cloak that makes objects invisible to magnetic fields and a “wormhole” that directs a magnetic field between two points in space along an invisible tunnel, as well as other things. Their latest material—which acts as a magnetic diode—enables unidirectional transfer of a magnetic field between two objects. Prat-Camps says that such a device could increase the efficiency of magnetic-based wireless power-transfer systems.

An electric current flowing through a coil of copper wire induces a magnetic field in the coil. This magnetic field can then transfer to a nearby magnetic object, such as a second coil of wire. The laws of electromagnetism, and experimental demonstrations to date, predict that this transfer is symmetric, meaning that magnetic fields move both from coil A to coil B and from coil B to coil A. Prat-Camps and his colleagues wondered if they could break this so-called magnetic reciprocity and make the magnetic-field transfer one way. The answer, they found, is yes, if both coils are placed in between the two walls of a hollow, rotating, conducting cylinder, where the walls have a U-shaped cross section.

In calculations and a proof-of-principle demonstration, Prat-Camps and colleagues showed that when the cylinder rotates at a constant velocity, a magnetic field from coil A can transfer to coil B, for example, but not the other way around. This nonreciprocity holds as long as the cylinder keeps spinning
. Prat-Camps says that their current device is bulky and impractical for everyday use, but the team is exploring other device designs.

This research is published in Physical Review Letters.
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