How do coded magnets work?

The one idea to hold onto: correlation

Coded magnets borrow a trick from radar and radio. Engineers there use special sequences - correlation codes such as the Barker code - that produce one sharp spike when two matching signals line up and almost nothing when they don’t. That “sharp when aligned, quiet when not” property is called good autocorrelation, and it is exactly what you want if you are trying to build a magnet that grabs hard in one position and lets go everywhere else.

Now apply it to magnetism. Treat North as “+1” and South as “−1.” A coded magnet writes a sequence like + + + − − + − across its face. Its matching partner carries the same sequence. When the two are aligned, every cell meets its like partner, all the little forces add up, and the pair snaps together. Nudge one magnet over by a single cell and suddenly many pairs are mismatched - a North now faces a South that wants to push it away. The forces fight each other and the net pull collapses, or even reverses into a shove.

How a coded magnet is made, in four steps

Why the force can attract and repel

This is the part that surprises people. With ordinary magnets, two North faces always repel and North-to-South always attracts - flip one over and the behavior flips too. Coded magnets break that rule because each face carries both Norths and Souths in a pattern. Whether the pair attracts or repels depends on how the two patterns line up, not on which way you flipped the magnet. Slide one magnet along its partner and you sweep through attract, cancel, and repel - the interactive strip on the home page lets you drag through exactly that.

From one code, many behaviors

By choosing the code and the offset, a designer sets which behavior a pair exhibits:

• Attach - matching codes aligned pull together hard, often stronger for their size than a plain magnet.
• Repel - a mismatched or shifted code turns the same faces into a controlled push.
• Spring / hold-at-a-distance - layered attract-and-repel codes settle at a fixed gap, like a contactless spring.
• Align - the correlation peak drags an off-center or rotated part into one exact position.
• Latch & release - firm in the aligned position, then a small twist drops the correlation to zero and it lets go.
• Coded-pair keying - a magnet engages strongly only with its matching code and ignores others.

See all six with swatches on the behaviors table, or watch them demonstrated on the videos page.

A note on the history

Correlated magnetics was developed by Larry Fullerton beginning in 2008 and commercialized under the Polymagnet brand by Correlated Magnetics Research. Fullerton’s background was in ultra-wideband radio, which is why the magnets borrow correlation-code ideas from the RF world.