In a first aspect, the disclosure features apparatuses for wireless power transfer, the apparatuses including a coil formed of a conductive material. The coil includes a plurality of loops, where the plurality of loops defines an internal region of the coil that extends along a coil axis. The apparatuses include a magnetic component, where the magnetic component is disposed in the internal region and extends in a first direction parallel to the coil axis and in a second direction perpendicular to the coil axis. A maximum dimension of the magnetic component measured in the second direction varies along the first direction.