field system; field magnet
Technical term in electrical engineering for the part of a motor, generator, or other electromagnetic device that produces the magnetic field, as opposed to the armature.
In DC motors, permanent magnets are often used for the field system.
界磁巻線に電流を流して磁界を発生させる。
A current is passed through the field winding to generate a magnetic field.
field winding
Compound of 界 (boundary, world, here meaning 'field') and 磁 (magnet). The exact derivation is uncertain, but the word is a modern technical coinage for 'field magnet' or 'field system' in electrical engineering.