Permanent Magnet: ON/OFF Mechanism...

[z_p_e]

You might try this circuit I whipped up tao.

It's perhaps somewhat crude, but it should work. I don't think cross-over in the output should be an issue since only square waves are going through.

z_p_e

Update: A capacitor has been added to minimize or eliminate DC offsets inherent in the level translator. -3dB is at 159 Hz.

[raburgeson]

Maybe square waves work because the resonant frequency fluxuates and the harmonics fill in the fluxuation.

[Esa Maunu]

This ON/OFF mechanism can be caused by the magnetic field that is crated by current flow through the magnet.
The magnetic field, created by current flow, is on 90 degrees with the direction of the current flow through the magnet, so it has a same  direction as there is in a permanent magnet. If the created magnetic pole by current flow is opposite with the permanent magnets pole, they cancel each other. Also,there is a possibility that magnetic flux lines are canceled out by cutting the magnetic field by sharp DC pulses.

Esa

[z_p_e]

The circuit has been updated with an added capacitor to eliminate any offsets in the level translator stage. This should work much better with virtually no DC offset.

http://www.overunity.com/index.php?topic=1119.msg12102;topicseen#msg12102

z_p_e

[Esa Maunu]

Opposing magnetic fields have a tendency to cancel each other.
But it is most likely that this effect occurs because of  sharp edges of the current pulses.Anyway it is clear that the frequency of the pulses must be high.

Esa