| 摘要 |
An electromagnetic apparatus comprises a magnetic assembly having an annular air gap, a wire coil, and an arrangement for energizing the coil only in the air gap, the magnetic assembly being disposed coaxially of the coil so that the coil is movable in the air gap relative to the magnetic assembly. The preferred coil is formed of a plurality of narrow segments axially adjacent and electrically connected in series, successive segments abutting one another, each segment being spirally wound from radially overlapping and abutting turns of wire, the abutting segments being alternately wound inwardly and outwardly such that adjacent sections spiral radially in opposite directions and being electrically connected so that current will flow in the same circumferential direction throughout the coil. The number of turns of wire in the air gap is maximized, ohmic heating of the coil occurs only in that portion which is energized in the air gap, and the magnetic force available from the coil in the air gap is maximized for a given magnetic flux density and a given coil current, while retaining linearity of force obtainable over the length of the coil. The coil segments may be separately formed and axially assembled, and wire of rectangular cross section preferably is used.
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