The winding pattern of a coil, most often a flat pancake spiral or a ring-shaped loop. From its measured field a coil is also classified as pancake (center-strong), donut (ring-strong), or loop.
How the wire is wound sets where the field is strongest. Each profile is a real measured cross-section. A pancake coil is a tight flat spiral, so its field stays strong across a broad center. A donut coil leaves a hole in the middle, so its field peaks in a ring and dips at the center. A loop coil is one large turn, so its field peaks over the wire ring and eases off toward the middle and the rim. Copper dots are the wire seen end-on.
