A solution of the present invention is to divide each back iron into segments such that there is {TAIL ~ a physical air gap} between the back iron segments of {HEAD ~ two adjacent magnet clusters} 
A solution of the present invention is to divide each back iron into segments such that there is { TAIL ~ a physical air gap } between the back iron segments of { HEAD ~ two adjacent magnet clusters }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD