relative angle is varied one degree every time. But it is considered
to be linear in one degree. Both the inner and outer annular
magnet still can be driven to rotate together by the three-phase
AC asynchronous motor when their relative angle is not varied.
The electromagnetic clutch A must be opened first, and then
closed the electromagnetic clutch B. As it to say, the velocity of
the magnetic field can be circumrotated at a scale which is from
1 to 20 cycles per minute. In Table II, the magnetic flux density
wanted and measured result is shown.