Long linear stroke reciprocating electric machine

A linear stroke reciprocating electric motor, comprising

• two relatively linearly movable members, mounted to be relatively movable with respect to each other in a movement direction along an axis about which each of said members is symmetrical, one of said members being an electric coil wound around said axis, and the other member being a magnetic gap ring having a gap-defining surface having a given length in said movement direction,
• a magnetic stator structure fixed to one of said relatively movable members and symmetrical alout said axis, said structure and said gap ring being gap-defining members, and said structure having a surface spaced from said gap-defining surface to define a gap therebetween, said electric coil being arranged in the gap between the gap ring and the stator structure, and said coil having a length in said movement direction substantially less than said given length,
• magnet means for producing a field flux across at least a portion of said gap,
• means for establishing electrical connection to pass electrical current through said coil, for urging relative motion between said relatively movable members in said movement direction, and
• a flux focusing ring, having a length in the movement direction substantially equal to said coil length, said focusing ring being formed of a magnetic material and arranged in said gap between the coil and one of said two gap-defining members, said focusing ring having a thickness compared to the gap width such that substantially all the field flux passes through the coil and the focusing ring, said focusing ring and said coil being fixed relative to each other,
• whereby relative movement of said coil and gap ring over a stroke equal to the difference between said given length and said coil length provides a long linear stroke, with substantially all the field flux and all the coil turns interacting over the entire stroke.