I have a 12 slot, 16 pole PM BLDC motor that exhibits a sinusoidal generated voltage.  The magnet consists of a ring magnetized with the 16 poles, full arc (as seen with viewing paper).  There is no skew to the stack or the magnets, and the air gap is not unusually large.  This configuration alone should not have a sinusoidal EMF with simple magnetization.  My question is:  How do you magnetize the magnets for a sinusoidal EMF.  I have heard of this being done, but I don't know the process.  Thanks for your help.