Coil, electrical system including the same and method of making coil

A coil comprising

• a multilayer film which is wound to form a plurality of loops which are substantially concentric,
• wherein the multilayer film comprises
• a plurality of first electro-conductive layers which are spaced apart from one another in a thickness direction;
• a second adhesive layer which is disposed between two or more adjacent first electro-conductive layers;
• and
• a third magnetic-conductive layer,
• wherein one or more of the plurality of first electro-conductive layers are disposed on the third magnetic-conductive layer,
• wherein the first electro-conductive layer, the second adhesive layer, and the third magnetic-conductive layer have a width and a length which are substantially coextensive thereamong, such that main coil surfaces, which are substantially planar, comprise corresponding end surfaces of the first electro-conductive layer, the second adhesive layer, and the third magnetic-conductive layer, respectively,
• wherein the two or more first electro-conductive layers have different average thicknesses to reduce an alternating current resistance of the coil by 3%-6.6% inclusive in a frequency of about 143 kHz or higher.

An electrical system comprising:

• a wireless charging system comprising a substantially planar coil which comprises a plurality of loops which are concentric;
• and
• an electrical circuit configured to be charged wirelessly by the wireless charging system,
• wherein each of the concentric loops comprises a metal layer which is substantially coextensive with the loop,
• wherein the metal layers of the two or more concentric loops have
• different average thicknesses to reduce a charging time spent by the wireless charging system by 3%-6.6% inclusive in a frequency of about 143 kHz or higher.