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A litz wire comprises three or more insulated strands consisting essentially of an inner conductor and an outer insulating layer on said conductor. The strands are twisted symmetrically with respect to the center line of the wire, so that a current density distribution in the litz wire becomes unifo

A litz wire comprises three or more insulated strands consisting essentially of an inner conductor and an outer insulating layer on said conductor. The strands are twisted symmetrically with respect to the center line of the wire, so that a current density distribution in the litz wire becomes uniform. Three or more such litz wires are twisted to form a composite litz wire. The composite litz wires are suitable for use in a high-frequency coil.

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1. In a litz wire for conducting high frequency current comprising a plurality of insulated strands which are twisted to form said wire, each of said strands consisting essentially of an inner conductor and an outer insulating layer on said conductor, the improvement comprising said wire being forme

1. In a litz wire for conducting high frequency current comprising a plurality of insulated strands which are twisted to form said wire, each of said strands consisting essentially of an inner conductor and an outer insulating layer on said conductor, the improvement comprising said wire being formed of three of said insulated strands which are twisted in such a manner that said strands are arranged concentrically in said litz wire whereby the loss resistance of the litz wire due to the skin effect when a high frequency current is conducted by said litz wire is greatly reduced. 2. In a litz wire for conducting high frequency current comprising a plurality of insulated strands which are twisted to form said wire, each of said strands consisting essentially of an inner conductor and an outer insulating layer on said conductor, the improvement comprising said wire being formed of three of said insulated strands which are twisted to form a fundamental unit wire of said litz wire, said three insulated strands being twisted in such a manner that said strands are arranged concentrically in said fundamental unit wire, and wherein a plurality of said fundamental unit wires are twisted to form said litz wire, said fundamental unit wires being twisted in such a manner that said fundamental unit wires are arranged concentrically in said litz wire. 3. A litz wire for high frequency current according to claim 2, wherein said plurality of fundamental unit wires are twisted around an axial member. 4. A litz wire for high frequency current according to claim 3, wherein a peripheral portion of said axial member is formed of an insulating layer and a central portion of said axial member is formed of a conductor for conducting a control signal instead of said high frequency current. 5. A litz wire for high frequency current according to claim 4, wherein an adhesive layer is provided at an outermost portion of said insulating layer of said axial member. 6. In a litz wire for conducting high frequency current comprising a plurality of insulating strands which are twisted to form said wire, each of said strands consisting essentially of an inner conductor and an outer insulating layer on said conductor, the improvement comprising said wire being formed by twisting said strands about an insulated axial member disposed along a center line of the litz wire with each of the strands being arranged concentrically in said litz wire and the number of said strands in said litz wire being at least four. 7. In a litz wire for conducting high frequency current comprising a plurality of insulated strands which are twisted to form said wire, each of said strands consisting essentially of an inner conductor and an outer insulating layer on said conductor, the improvement comprising said wire being formed of at least four of said insulated strands which are twisted around an insulated axial member to form a fundamental unit wire where said insulated axial member is disposed along a center line of said fundamental unit wire, said at least four insulated strands being twisted in such a manner that said strands are arranged concentrically in said fundamental unit wire, and wherein at least three fundamental unit wires are further twisted to form said litz wire, said fundamental unit wires being twisted in such a manner that said fundamental unit wires are arranged concentrically in said litz wire. 8. A litz wire for high frequency current according to claim 7, wherein said fundamental unit wires are twisted around a second axial member. 9. A litz wire for high frequency current according to any one of claims 6, 7 and 8, wherein a peripheral portion of said axial member is formed of an insulating layer and a central portion of said axial member formed of a conductor for conducting a control signal instead of said high frequency current. 10. A litz wire for high frequency current according to claim 9, wherein an adhesive layer is provided at an outermost portion of said insulating layer of said axial member. 11. In a litz wire for conducting high frequency current comprising a plurality of insulated strands which are twisted to form said wire, each of said strands consisting essentially of an inner conductor and an outer insulating layer on said conductor, the improvement comprising at least one fundamental unit wire of said litz wire formed with at least three of said insulated strands, each of said insulated strands of said fundamental unit wire being concentrically arranged with respect to and twisted about the center line of said fundamental unit wire as seen in cross section whereby the loss resistance of the litz wire due to the skin effect when a high frequency current is conducted by said litz wire is greatly reduced. 12. A litz wire according to claim 11, wherein at least three of said fundamental unit wires are concentrically arranged and twisted with respect to each other to form a composite wire. 13. A litz wire according to claim 12, wherein at least three of said composite wires are concentrically arranged and twisted with respect to each other to form said litz wire.