Variable magnetic layer for wireless charging

A magnetic film assembly comprising:

• a coil comprising a plurality of turns defining a first major boundary surface of the coil, such that when energized, the coil generates an in-plane magnetic field component in a region of interest in air proximate and substantially parallel to the first major boundary surface, the in-plane magnetic field component having a magnetic field strength H that varies between a maximum Hmax and about 10% of Hmax in the region of interest in air, wherein the region of interest comprises a line segment in air that is immediately adjacent and parallel to the first major boundary surface and that extends between first and second endpoints proximate outermost turns of the coil and a midway point aligned with a center of the coil;
• and
• a magnetic layer disposed on the coil so as to comprise the region of interest, such that when energized, the coil generates, in the region of interest, an in-plane magnetic field component having a magnetic field strength H that decreases from a maximum Hmax at a location adjacent at least one of the outermost turns of the coil to not more than 0.10·Hmax at a location adjacent the center of the coil, and the magnetic layer is configured such that, in the region of interest, an induced in-plane magnetic flux density B varies by no more than 5% over the region of interest, wherein the magnetic layer comprises a plurality of discrete magnetic segments arranged along length, width, and thickness directions of the magnetic layer, the magnetic layer comprising a central region proximate a center of the coil, a peripheral region proximate a periphery of the coil, and a middle region disposed between the central and peripheral regions,
• the magnetic layer having respective average thicknesses Tcen, Tmid, and Tper in the central, middle, and peripheral regions such that Tmid is greater than Tcen and greater than Tper.