ferromagneticcore

A ferromagnetic core is a solid piece or assembly of ferromagnetic material used to provide a low-reluctance path for magnetic flux in magnetic circuits. By concentrating flux and increasing permeability, such cores raise inductance in windings and improve transformer efficiency by reducing magnetic leakage.

Common core materials include iron and iron-based alloys (such as silicon steel and nickel–iron alloys like permalloy), as well as ferrites. Cores may be solid or laminated to reduce eddy currents, or made from powdered iron bound in epoxy to create distributed gaps. Ferrite cores, made of ceramic ferrites, offer high electrical resistivity and are especially suited for high-frequency applications, while laminated steel cores are favored in low-frequency power transformers and large inductors.

Ferromagnetic cores exhibit nonlinear magnetic behavior characterized by a B–H hysteresis curve. They have a saturation flux density Bsat, a remanent flux density, and a coercive field. Permeability is high at low flux, but declines as the core approaches saturation. The performance is temperature dependent; rising temperature reduces permeability and the Curie temperature marks the loss of ferromagnetism.

Losses in cores arise from hysteresis and eddy currents. To minimize losses, designers select materials with low coercivity and high resistivity, and control the geometry. Laminations, thin sheets, reduce eddy currents; ferrites minimize eddy losses at high frequency. At high power levels, core design also considers saturation, flux density, and allowable temperature rise.

Applications include power and signal transformers, inductors and chokes, motors and generators, electromagnets, and magnetic shielding components in electronics. The term ferromagnetic core encompasses various configurations from toroids and E-cores to pot cores and laminated sheets.