Magnetism May Cure the Achilles’ Heel of Big Mechanical Devices

The most sophisticated machinery in the world today, ranging from hard disk drives in computers to turbine engines in jet aircraft, all depend on something quite mundane to keep working. Without bearings to allow one part to move smoothly against another, all of them will fail, sometimes with spectacular results.

Now, one of the grand old men of science says he has come up with a better way to build bearings using something as simple as permanent magnets, such as those used to hold the kids’ latest artwork on the refrigerator.

Four days every week, 81-year-old Richard F. Post returns to Lawrence Livermore National Laboratory, where he has labored for so many years to develop magnetic nuclear fusion as an energy source. Post says he has turned his attention now to a “passive bearing system” because, quite frankly, he knows he won’t be around long enough to see a fusion power plant.

“I spent almost all my professional career on magnetic fusion, and I’m not going to see magnetic fusion in my lifetime,” he says.

“I would like very much to see something in my lifetime that I worked on,” he adds with a robust laugh.

So he returns faithfully to the lab nearly every day, working on a project that Popular Mechanics magazine recently labeled as potentially “the most significant mechanical device of the 20th century.”

But to get to where he is today, he had to figure out how to circumvent a key law of physics postulated in 1839 by the Rev. Samuel Earnshaw.

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Earnshaw’s Theorem, as it came to be known, says basically that it’s impossible to levitate one permanent magnet above another and keep it there without some form of restraint.

Anyone who has ever played with refrigerator magnets knows Earnshaw was right. Like poles repel each other, one magnet held above another will try to keep a space between the two. But let go of it, and it will slip off to the side like a lump of butter on a hot knife.

That’s a shame, because if it could somehow be forced to stay there, the separation between the two magnets would provide an electromagnetic bearing that would never need oiling and would last almost forever. If the upper magnet could be started spinning, there would be no friction to slow it down, and only its inertia would eventually stop it.

Recognizing that, scientists began several decades ago to develop active sensors that could nudge the upper magnet back into position whenever it strayed ever so slightly, and that has led to a worldwide industry that produces active magnetic bearing systems for industrial use.

But Post and a colleague, Jerry Smith, wanted to take that a step further. A passive system, without the need for active sensors, would be far more efficient and cheaper and would require absolutely no maintenance.

Post is the father of a magnetic levitation train that is being developed by the Livermore Lab, and he borrowed from that research to come up with a solution to Earnshaw’s Theorem. The so-called maglev train uses a permanent-magnet array known as a “Halbach array,” named after the Lawrence Berkeley Laboratory physicist, Klaus Halbach, who invented the configuration for use in focusing particle beams in nuclear accelerators.

In an early experiment, Post and Smith placed disk magnets at both ends of a metal shaft.

“At the bottom end of it I stuck a pair of repelling disk magnets which would levitate it, and at the top end another pair so it was sort of caught between these two,” Post says. “That’s just fine as long as it’s standing directly vertical right in the middle. But if I let go of it, it would just fall sideways.”

So they put a doughnut-shaped Halbach array around each end of the shaft. Then they attached a coil of wires to each end of the shaft, just inside the Halbach array.

As the shaft turned inside the array, the Halbach magnets induced an electric current in the wires, which in turn produced another magnetic field.

If the shaft leaned in one direction, it encountered the magnetic field from the wires.

“If one side got closer to the wires than the other, it got pushed back,” Post says. The result was the spinning shaft remained levitated between the disk magnets, and the Halbach array kept it centered.

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Earnshaw had not been proven wrong. But Post and Smith had used one law of physics--a magnetic field can induce a current, which in turn produces a magnetic field--to supersede another, Earnshaw’s Theorem.

Post had the system patented, and the Lawrence Livermore Lab is now working with a Livermore firm, Trinity Flywheel Power, to develop flywheels as stored energy devices, using the lab’s technology. That work is being funded chiefly by the National Institute of Standards and Technology.

The technology offers several advantages over mechanical bearings, mainly in the loss of energy (and production of heat) through friction. Bearings are the Achilles heel of many mechanical devices, often limiting the lifetime of the equipment, and frequently causing shutdowns for repairs and maintenance.

Post believes the passive magnetic bearing system would save enough during the lifetime of an industrial motor, for example, to pay for another motor.

You are probably never going to see this technology in common household appliances, such as mixers, because cheap ball bearings can do the job. But Post is convinced that you will see it in many applications ranging from industrial motors to space-based devices and equipment that is hard to reach for servicing.

It may even find a place in hard drives.

Hopefully, Dick Post will still be around to see it.

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Lee Dye can be reached at leedye@ptialaska.net.