Patent ID: 6847284

Claim:
A planar coil comprising a winding formed by arranging a conductor into a flat-spiral shape, the winding including winding portions of N turns (N is an integer greater than or equal to two), wherein: letting r i (n) be a radius of an inner circumference of a winding portion at the n th turn (n is an integer greater than or equal to one and less than or equal to N) from the inner side; r o (n) be a radius of an outer circumference of the same; r min be a radius of an inner circumference of the innermost winding portion; W total be a difference between a radius of an outer circumference of the outermost winding portion and the radius of the inner circumference of the innermost winding portion; and D be a distance between winding portions at adjacent turns, the r i (n) and r o (n) are determined so as to minimize a value of A expressed by equation (1) when the r min , W total and D are given: A = ∑ n = 1 N ⁢ ( log ⁢ r o ⁡ ( n ) r i ⁡ ( n ) ) - 1 ( 1 ) where r i ( 1 )=r min , r i (n+1)−r o (n)=D, and r o (N)−r i ( 1 )=W total .