The transmission of a Moon Crescent shape

At first the Brush enters the Guiding Compass. The positive magnetic field affects mainly INWARDS. This is why the Brush has no problems penetrating the Barrier.
Inside the positive Compass the Brush (that also has a positive charge) is forced to take a spiral path.
When it meets the Control Compass, it suddenly receives missing electrones and its charge diminishes (probably isn't completely removed, because then the plasma would disintegrate). This cools down the plasma so that it doesn't bend the stalks anymore.
Inside the C-compass the Brush is slightly drawn to the left and towards the compass perimeter. When it re-enteres the positive zone, the field sucks electrones from it making its charge increase. The Brush heats up again and continues laying down the crop.
All the time both the sound barriers within the Compasses protect the surrounding crop from the air current.
Finally the compasses are released and the Brush escapes.