Magnetic Levitation

 

Magnetic levitation is a concept which still sounds like magic to most people, despite its introduction in infrastructure and gadgets around the world - the most popular being the maglev train.

Maglev trains utilize a strong magnetic field in the rail to suspend a train using the forces of repulsion, and to propel the train using both repulsion and attraction.


High speed maglev train
(Image courtesy of FYS)


Bismuth - a diamagnetic material

While maglev trains operate using electromagnets, the same effects can be demonstrated using static magnets, which is will be demonstrated here.

Some metals are attracted by both poles of a magnet, such as iron. These metals are known as ferrous metals.

However, there exists another group of metals which have a property called diamagnetism. Materials such as bismuth, carbon, graphite and aluminium possess this weird property. Diamagnetic materials are seen to slightly repel both poles of a magnet.

The idea behind diamagnetic levitation in the lab is to levitate a small, but very powerful neodymium magnet between two layers of diamagnetic material. This is done by attracting the small magnet using a larger one above the top piece of diamagnetic material.

As the big magnet pulls the small one up, it arrives at an equilibrium state whereby the small magnet has enough force to overcome gravity, but not enough to overcome the additional repelling forces posed by the top piece of diamagnetic material. Thus it appears to hover in mid air.


Location of neodymium magnets inside a hard disk
(Image courtesy of Renewable Energy UK)

Powerful rare-earth neodymium magnets are found in hard disks, CD-rom drives and speakers.

They'll be pretty easy to find in an old hard disk (may need a hammer to bust it open first though), but in a CD-drive you will have to completely dismantle the optical mechanisms PEACEFULLY (avoid the hammer this time). They can be harder to get out of speakers.

As with any salvage job, patience is a virtue.

Although bismuth is by far the best material for this demonstration and provides the best results, it is relatively expensive and hard to come-by. In the mean time... aluminium will have to do. It sucks, and it's tricky to set up, but it works.

Here's the setup in real life. Compare it to the above diagram to see the similarities.

And.... results! Hovering a mere fraction of a millimeter above and below the aluminium disks.

Now here is possibly the easiest, fastest, and cheapest form of magnetic "levitation" ever!

The ring magnets in the photo are magnets from a dismantled magnetron - the heating element in microwave ovens. If you do go salvaging these, they can be found in-between the magnetron cooling fins. A hammer is useful for doing the hard work, provided you don't go smash your way through the magnets themselves.

These magnetron magnets have a lower power density relative to neodymium magnets, but because they are quite large, still pack a lot of punch.

To put this quick and easy demonstration together, a PVC pipe of suitable diameter is simply placed into the rings of a few magnets which serve as a base.

Another magnet is placed through the PVC pipe in the opposite way so that it repels the 'base' magnets.

Note that if the PVC pipe wasn't there, the top magnet would just flip over and snap straight onto the base magnets, and you would probably end up with shards of magnet all over the floor. Though I would like to see this done with transparent PVC tube!

Or... using only a couple of magnets as a base, the rest of them can be suspended in a S-(NS)-(SN)-(NS)... configuration, so that all magnets repel each other.

The width of the gaps between the magnets seem to follow some sort of natural growth trend, although there is a clearly a limiting factor as the top magnet cannot be suspended anymore than its repelling power allows it.

The gaps are evidently smaller towards the base, as the lowest magnet has to carry the weight of all the magnets above it.

 

 

 

 

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