An interesting reply post from a guy in Sweden:

<h3><table align="center" width="98%"><tr><td class="small">Quote </td><td width="99%"><hr/></td></tr><tr><td colspan="2" class="small">this switched DC changes from full + to full - instantly. <hr/></td></tr></table>
If it had said it is shifting between full + and zero instantly. It would have been DC.

But then you change polarity it's AC no matter the form of the curve! AC when you pass zero. DC when you don't reverse the electron flow. You can go to zero but not reverse the flow!

So if you only push OR drag the magnets you use DC. But if you push AND drag you use AC!

So you can use both type of waves. For DC minimum is zero and for AC it is as much negative as positive. Depend how much force you wanna have your electrons to make!

Here you can see <font color="#810081">DC on wikipedia</font> and <font color="#810081">AC on wikipedia.</font></h3>