Coil, planar coil and method for making coil

A coil comprising:

• main coil surfaces which are opposite each other and are substantially planar;
• and
• a multilayer film which is wound to form a plurality of loops which are substantially concentric,
• wherein the plurality of loops comprise an innermost loop comprising a first longitudinal direction end of the coil, and an outermost loop comprising a second longitudinal direction end of the coil,
• wherein the multilayer film comprises a plurality of first electro-conductive layers which alternate with each other, and one or more second electrical insulation layers,
• wherein the first electro-conductive layer and the second electrical insulation layer have a length which is substantially coextensive therebetween along a winding direction of the coil, and have a thickness which is substantially coextensive along a thickness direction of the coil, such that the main coil surfaces, which are substantially planar, comprise corresponding end surfaces of the first electro-conductive layer and the second electrical insulation layer, respectively,
• wherein the multilayer film has respective average widths W1, W2 along a first in-plane direction and a second in-plane direction of one or more of the main coil surfaces which are planar,
• wherein the multilayer film has average widths W3, W4 along two or more directions which form an angle of 20° to 160° inclusive therebetween, and wherein a width difference between the average widths in the two or more directions belongs to 0% to 10%,
• wherein the first in-plane direction and the second in-plane direction have an angle of 90° therebetween,
• wherein 11.47≥W1/W2≥1.02.