Järnkärna

Järnkärna, or iron core, is a magnetic core used in electromagnetic devices to route and intensify magnetic flux. Made from soft magnetic materials with high permeability and low coercivity, järnkärnor reduce magnetic reluctance and form a closed magnetic path that improves coupling between windings and increases inductance.

Common materials include silicon steel laminations, soft iron, and ferrite. Laminations are thin metal sheets insulated from each other to limit eddy current losses; shapes include lamination stacks, toroidal cores, and open- or closed-loop geometries such as E-cores, U-cores, and C-cores.

At low frequencies, iron cores made of silicon steel or laminated iron provide high permeability, allowing efficient transformers and inductors. At higher frequencies, ferrite or powdered-iron cores are preferred due to higher resistivity, which reduces eddy current losses.

Key performance factors include magnetic permeability, saturation flux density, hysteresis losses, and eddy currents. Saturation limits the maximum flux; hysteresis losses arise from magnetization cycles, while eddy currents circulate within the core material and cause heat. Design often uses lamination, ferrite composition, and core geometry to balance efficiency, size, and cost.

Applications include transformers, inductors, chokes, electromagnets, and electric machine cores in motors and generators. In transformer design, the iron core concentrates flux from the primary coil to the secondary, enabling efficient energy transfer. In inductors, a järnkärna increases inductance and reduces device size for a given current and frequency.