a method for winding a coil on an object , wherein the coil includes a plurality of first coils and a plurality of second coils , may have winding the first coils on an exterior circumferences of the second coils , wherein an outer circumferences of the respective second coil is enclosed and in contact with outer circumference of at least three first coils , and wherein cross - sectional area of the second coil is smaller than that of the first coil , and wherein the outer circumference of the at least three first coils are in contact each other .