Systems and methods for improving winding losses in transformers are disclosed. In one aspect, a transformer includes a first magnetic core having an interior portion and an exterior portion, a second magnetic core in contact with the interior and exterior portions, a plurality of primary and secondary windings formed around the interior portion, where the interior portion is formed from one of a first magnetic material and a second magnetic material, and the exterior portion is formed from one of the first magnetic material and the second magnetic material, where the first magnetic material has different properties than the second magnetic material. In another aspect, the first magnetic core includes a third portion that extends across and is in contact with the interior portion and the exterior portion, where the third portion is formed from one of the first magnetic material and the second magnetic material.

A coil electronic component includes a magnetic body having an internal coil part embedded therein, in which the internal coil part includes an insulating substrate, a first insulator, a coil conductor, and a second insulator. The first insulator is disposed on at least one of first and second main surfaces of the insulating substrate and has a groove formed therein. The coil conductor is formed inside the groove. The second insulator encloses the insulating substrate, the first insulator, and the coil conductor. The first insulator may be formed to a thickness larger than (and no more than 40 μm thicker than) a thickness of the coil conductor on the insulating substrate. The first insulator may be formed to a width of 3 μm to 50 μm. Further, the second insulator may extend to a thickness 1 μm to 20 μm larger than that of the first insulator on the insulating substrate.

A coil electronic component includes a magnetic body having an internal coil part embedded therein, in which the internal coil part includes an insulating substrate, a first insulator, a coil conductor, and a second insulator. The first insulator is disposed on at least one of first and second main surfaces of the insulating substrate and has a groove formed therein. The coil conductor is formed inside the groove. The second insulator encloses the insulating substrate, the first insulator, and the coil conductor. The first insulator may be formed to a thickness larger than (and no more than 40 μm thicker than) a thickness of the coil conductor on the insulating substrate. The first insulator may be formed to a width of 3 μm to 50 μm. Further, the second insulator may extend to a thickness 1 μm to 20 μm larger than that of the first insulator on the insulating substrate.

An inductive filtering device includes a first toric magnetic core without an air gap formed around a central void; a first electrical conductor formed of turns that are wound around the first magnetic core without passing through the central void, wherein no electrical conductor passes through the central void.

A coil component includes a magnetic body containing metal magnetic particles; a coil embedded in the magnetic body; and an outer electrode at at least the bottom surface (for example, a first main surface) of the magnetic body and electrically connected to the coil. The outer electrode (for example, a first outer electrode) includes, in order from the side of the magnetic body, an underlayer containing Ag, and a plating layer. At an interface between the magnetic body and the underlayer, an oxide film containing a metal element contained in metal magnetic particles is between the metal magnetic particles and the underlayer. In the inside of the magnetic body, an oxide film having a thickness smaller than the thickness of the oxide film between the metal magnetic particles and the underlayer is at surfaces of metal magnetic particles adjacent to the metal magnetic particles positioned at the interface.

A coil component includes a magnetic body containing metal magnetic particles; a coil embedded in the magnetic body; and an outer electrode at at least the bottom surface (for example, a first main surface) of the magnetic body and electrically connected to the coil. The outer electrode (for example, a first outer electrode) includes, in order from the side of the magnetic body, an underlayer containing Ag, and a plating layer. At an interface between the magnetic body and the underlayer, an oxide film containing a metal element contained in metal magnetic particles is between the metal magnetic particles and the underlayer. In the inside of the magnetic body, an oxide film having a thickness smaller than the thickness of the oxide film between the metal magnetic particles and the underlayer is at surfaces of metal magnetic particles adjacent to the metal magnetic particles positioned at the interface.

An inductor includes a coil that is constituted by a conductor having a coating layer and includes a winding portion where the conductor is wound and an extended portion extended from the winding portion, a base body that envelops the coil and is constituted by a magnetic body containing magnetic powder and resin, and an outer electrode that is arranged on a surface of the base body and connected to the extended portion. The extended portion of the coil includes a conductor portion that does not have the coating layer in an end portion of the extended portion, and the conductor portion includes a first region connected to the outer electrode and a second region in contact with the magnetic body.

An inductor includes a coil that is constituted by a conductor having a coating layer and includes a winding portion where the conductor is wound and an extended portion extended from the winding portion, a base body that envelops the coil and is constituted by a magnetic body containing magnetic powder and resin, and an outer electrode that is arranged on a surface of the base body and connected to the extended portion. The extended portion of the coil includes a conductor portion that does not have the coating layer in an end portion of the extended portion, and the conductor portion includes a first region connected to the outer electrode and a second region in contact with the magnetic body.

A coil component includes a body having one surface and the other surface and a plurality of wall surfaces, first and second insulating substrates spaced apart from each other, first and second recesses disposed in both end surfaces of the body and extending to one surface of the body, first and second coil portions disposed on the first and second insulating substrates, one ends and the other ends of the first and second coil portions being exposed to the first and second recesses, first and second external electrodes disposed along an inner surface of the first recess and one surface of the body and connected to one ends of the first and second coil portions, and third and fourth external electrodes disposed along an inner surface of the second recess and one surface of the body and connected to the other ends of the first and second coil portions.

A coil component includes a body having one surface and the other surface and a plurality of wall surfaces, first and second insulating substrates spaced apart from each other, first and second recesses disposed in both end surfaces of the body and extending to one surface of the body, first and second coil portions disposed on the first and second insulating substrates, one ends and the other ends of the first and second coil portions being exposed to the first and second recesses, first and second external electrodes disposed along an inner surface of the first recess and one surface of the body and connected to one ends of the first and second coil portions, and third and fourth external electrodes disposed along an inner surface of the second recess and one surface of the body and connected to the other ends of the first and second coil portions.