A disc-shaped coil wound in a spiral, often with multiple layers of windings stacked on top of each other. The layered turns reinforce each other, producing a strong, focused magnetic field that projects outward from the face of the coil. Field strength peaks at the center and drops off toward the edges, making it well suited for targeted application to a specific area. The field is delivered by placing the coil face against or near the target tissue. Identified by a peak at or near the center.
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.
