Magnetic diode?

Question

Non-reciprocal electromagnetic devices are fairly common but not static magnetic devices; reciprocity tells us that the coupling between two coils must be the same from one to the other as from the other to the one.

This paper claims to have found a way to break that symmetry:

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It is modestly titled:

"Circumventing Magnetostatic Reciprocity: a Diode for Magnetic Fields"

I've skimmed through it and while some of the math is beyond my rusty competence but I didn't see any obvious "divide by zero" or other unphysical boo-boos.

(There's a kind of "trick" involving a moving conductor near two otherwise non-moving coils but I think that can be similarly done with a time-varying field in a static conductor.)

Anybody? Does this break some conservation law? Possible applications?

Mark L. Fergerson

Phil Hobbs · Accepted Answer

I think that's the same principle as the shaded-pole motor, circa 1890.

Consider two coils whose axes are parallel but offset by some distance, with a rapidly rotating copper disk between them. Say coil 1 is at the left, coil 2 is at the right, and the disk is rotating left to right.

An AC current in coil 1 will induce a rotating current in the disk, which will be carried towards coil 2 by the disk. An AC current in coil

2 will do the same, except that the rotating current will be carried away from coil 1. Thus the resulting coupling will be different.

Calling that "breaking the Lorentz reciprocity principle" is a bit hyperbolic.

Cheers

Phil Hobbs

John Larkin · Answer

Given a power supply, I can accomplish the non-reciprocal coupling with a little electronics. --  John Larkin   Highland Technology, Inc   trk jlarkin att highlandtechnology dott com

Alan Folmsbee · Answer

Two iron magnets repel each other with less force than the force of those two magnets when they attract each other. Alan Folmsbee

Joseph Gwinn · Answer

On Nov 21, 2018,  wrote (in article): Reminds me of an acoustic circulator published in 201$: . The key was spinning media. Question is if what works with acoustic waves also works for EM waves. The  doppler effect works differently, because they speed of sound can be  exceeded. Joe Gwinn

bill.sloman · Answer

Nothing non-reciprocal about that. When the magnets are attracting one another the magnetic field from the first magnet intensifies the magnetic field in the second magnet.

When the same two magnets are repelling one another the magnetic field from the first magnet diminishes the magnetic field in the second magnet.

Magnetic diode?

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