Field element

A field element comprising:

• a plurality of permanent magnets circularly disposed about a predetermined axis;
• a first magnetic member being in contact with a magnetic pole surface of one of said permanent magnets in a first direction parallel to said axis;
• a first non-magnetic member which is adjacent to said first magnetic member in a second direction being a circumferential direction with said axis being as a center and overlaps a part of said one of said permanent magnet in said first direction;
• a second magnetic member being adjacent to said first non-magnetic member on a side opposite to said first magnetic member in said second direction;
• and
• a second non-magnetic member being adjacent to said second magnetic member on a side opposite to said first non-magnetic member in said second direction,
• wherein when Pn represents the number of pairs of magnetic poles provided by said permanent magnets about said axis and i represents an integer equal to or more than three, a first angle θ1 defined by a boundary between said second magnetic member and said second non-magnetic member in said second direction with respect to a reference axis which passes through a midpoint between another one of said permanent magnets being adjacent to said one of said permanent magnets on said second non-magnetic member side and said one of said permanent magnets and which is parallel to a radial direction with said axis being as the center, and a second angle θ2 defined by a boundary between said first magnetic member and said first non-magnetic member in said second direction with respect to said reference axis with said axis being as the center satisfying:
• 0<θ1<180/(i·Pn);
• and
• (i·Pn)≦θ2≦180·2/(i·Pn).