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Build a Halbach Array

And a one-sided refrigerator Magnet!

The late Klaus Halbach of Lawrence Livermore National Laboratories discovered an interesting permanent magnet configuration that concentrates magnetic flux on one side of the array and cancels it on the other. He originally designed it for focusing the beams of particle accelerators. LLNL scientists Post and Ryutov developed the idea into a model Maglev train, the only one so far that uses permanent magnets--it floats over a series of short-circuited coils at only 5 mph or so (the 'Inductrack' system). Maglev trains, motors and generators using circular Halbach arrays have already been patented--the advantages include minimized drag from eddy current effects (drag decreases as speed increases), reduced power consumption (no giant electromagnets needed), reduced exposure of train passengers to high magnetic fields, and other things that we haven't even begin to explore yet.

Our only result from experimentation so far has been a one-sided refrigerator magnet. Though it seems trivial at first, this magnet array seems frighteningly close to a magnetic monopole...it was enough to freak out the entire Wondermagnet.com staff!

One side of it sticks to the fridge....but the other does not.

Arrangement of magnets in a simple Halbach array

Halbach Magnet Array

Magnetic Flux Diagram of a Halbach Magnet Array

Halbach Array Flux Diagram

Illustrations used by permission from DMBoss1021@aol.com--thanks!

To build our strange, one-sided refrigerator magnet, we simply routed out a slot in a piece of wood to accept 5 of our Item #12, a 7/16 inch Neodymium-Iron-Boron cube magnet. The magnets are difficult to place in the correct pole configuration--they want to violently rotate into a N-S arrangement! First, mark the polarity of each magnet of the array by testing it against another magnet. Observe the first diagram above for the proper polarity configuration. It does not matter which pole is North and which is South, only that the poles you mark are the same, and that they match the diagram above.

Using a C-clamp to hold a magnet down into the slot, and another C-clamp to push each magnet toward the next, each magnet can be affixed into the slot in the proper polarity configuration using cyanoacrylate glue and accelerator, also available from us. Place one magnet at a time, and glue into the slot. If you try to clamp and glue all of them down at once, they will rotate out of the proper alignment and your experiment will fail!

In the photos below, the side that says 'augments' will stick to the fridge...but the side that says 'cancels' will not!

Homemade Halbach Array