An open electromagnetic coil designed to be placed around a limb or curved around a body part. The magnetic field passes through from all sides simultaneously. Unlike the enclosed donut coil, a loop is open. Limbs can be passed through it for surrounding coverage of arms, legs, or joints. The field profile is similar to a donut coil with peak strength in the ring zone. The open geometry allows flexible placement. Measurements are taken at 50% of the tubing thickness from the surface.
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.
