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Science for Friday? Sure thing! Anybody remember Halbach arrays?

Sure you do, we all do...

Now remember that a similar technique can be used to make a magnetic face which has a pattern of different magnetic strengths and polarities. Two such faces could be made to click together when in the same orientation... or repel when at 180 degrees (or any degrees, really). Moreover, by making them rotationally differentiated, you could have them spin to orient themselves to one of the "valid" interlock positions.

As an easy example, imagine those old U-bend magnets where one tip is + and one is -. Put two of them in a vice arranged such that the vertical face is four tips, arranged

- +
+ -

Now, make another one of those. These two faces want to repel at certain orientations and attract at others. Also, they will tend to spin to lock together cleanly. You can add a lot of complexity to this by adding more complex structures.

In fact, you can add very complex structures to get very complex behavior.

For example, imagine you have created a "target" surface where there are rings, each of which has the opposite polarity. Create an exactly opposite face and bring them towards each other.

At even a small distance, the magnetic pull is essentially zero, because the rings are equal and opposite and very close to each other. The thinner each ring, the shorter the range before the fields cancel out. However, when brought very close together, the opposing faces stick extremely tightly! Magnetic glue - no significant force at a distance, lots of force within a millimeter.

Lots more!

Instead of the magnetic surface consisting of poles facing "out" of the surface, imagine a simple ring system where the rings are pointed somewhat "away" from or "towards" the center of the rings. Imagine faces where the patterns on any given patch resolve differently depending on range. In either case, you can create a "sweet spot": any further away, the magnets are attracted. Any closer, they are repelled!

Imagine a magnetic face that could shift how it was magnetized, and therefore rotate, repel, and attract a specially made target face... loading bays where the crates are all moved by ceiling-mounted magnets and there are no forklifts. Load up the trucks with a "magnetic tether" that just reaches right through the top of the trailer.

Or, if you want to go old-tech, charging someone's flywheel car by hooking up to the magnetic interface and spinnnnnnnnnning. Or how about oldschool magtape computers where the instructions change depending on how closely you read the tape...

You can make science fiction out of anything.
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