Document 1, wherein said regions made of {HEAD ~ magnetic material} are spaced by {TAIL ~ magnetically blank portions} 
Document 1 , wherein said regions made of { HEAD ~ magnetic material } are spaced by { TAIL ~ magnetically blank portions }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL