magnetic circuit

Magnetic field (green) induced by a current-carrying wire winding (red) in a magnetic circuit consisting of an iron core C forming a closed loop with two air gaps G in it. In an analogy to an electric circuit, the winding acts analogously to an electric battery, providing the magnetizing field H, the core pieces act like wires, and the gaps G act like resistors. B – magnetic field in the core BF – "fringing fields". In the gaps G the electric field lines "bulge" out, so the field strength is less than in the core: BF < B BL – leakage flux; magnetic field lines which do not follow complete magnetic circuit L – average length of the magnetic circuit. It is the sum of the length Lcore in the iron core pieces and the length Lgap in the air gaps G.

A magnetic circuit is made up of one or more closed loop paths containing a magnetic flux. The flux is usually generated by permanent magnets or electromagnets and confined to the path by magnetic cores consisting of ferromagnetic materials like iron, although there may be air gaps or other materials in the path. Magnetic circuits are employed to efficiently channel magnetic fields in many devices such as electric motors, generators, transformers, relays, lifting electromagnets, SQUIDs, galvanometers, and magnetic recording heads.