Jeff's Diamagnetic Levitation
Demonstrator
A rig I built in
2003 to demonstrate
diamagnetic
levitation. Diamagnetic materials repel magnets, without regard to the
polarity of the magnet. The effect is much weaker than the attraction
of
magnetic materials to magnets, but it is strong enough to observe in
some materials such as bismuth. The diamagnetic materials in this demo
are
two bismuth plates spaced 7 mm apart with aluminum standoffs.
I cast the plates in the
recessed bottoms of a couple of soft drink cans. Bismuth in the form of shotgun shot is available from reloading
supply dealers or it can be found in small quantity lots on ebay.
A 2 mm cube shaped high energy magnet is placed between the plates. If the bismuth plates and that little magnet were located in a zero gravity environment the magnet would be repelled by both bismuth plates and assume a stable position midway between them. However, here on earth the pull of gravity on that little magnet is greater than the diamagnetic repulsion from the lower bismuth plate and the little magnet needs some help to let it float.
A strong suspension magnet located a few inches above the bismuth plates attracts the little magnet just enough to offset its weight. A knob at the top of a threaded mounting rod permits adjusting the location of the suspension magnet until the little magnet floats halfway between the two bismuth plates. The suspension magnet is far enough away from the bismuth assembly so that the strength of its magnetic field is nearly constant over the short distance between the bismuth plates.
When the suspension
magnet is adjusted correctly the little magnet
assumes a free floating stable position between the two plates. If it
tries to rise or fall, the diamagnetic
repulsion of the upper or lower bismuth plate pushes it back to the
center
again. It is fun see a solid object "floating in air" touching nothing
else, right before your
eyes, without needing any electronics, servomechanisms or
cryogenics to help it float.
The adjustment of the
suspension magnet is quite critical. If the demo is set up so the
little magnet floats between the bismuth plates while it is
on a wooden desk and then moved onto the top of a
steel
file cabinet. the steel distorts the
field of the suspension magnet enough to require a little readjustment
to get it floating again.
The web site below sells materials and has more information about diamagnetic levitation: