Engr. Abbas Abbasi

Behavior of Ferromagnetic MaterialsSaturation and Hysteresis

Ferromagnetic Material A material whose permeability is very much larger than 1 (from 60 to several

thousand times ), and which exhibits hysteresis phenomena

Material that acquires strong magnetism when placed in an external magnetic field. Examples are iron, cobalt, nickel, and their alloys.

MMF (DC ) Vs Flux Curve

If MMF (Ni) is increased flux also increases There comes a stage when increase in MMF does not produce corresponding

increase in flux The plot above is known as “Magnetization curve” of the core

Saturation

Saturation Region

Unsaturated region

cF Hl F H

BA B

B-H Curve

cF Hl F H

BA B

B-H Curve and Permeability (µ)

Permeability is the slope of the “Magnetization curve”

Constant permeability

Low and unstable permeability

MMF (AC ) Vs Flux Curve

F

φ

Hysteresis Loop

Magnetic Domains (Reason for hysteresis) Within the metals there are very small regions called domains In each domain atoms are aligned, with their magnetic fields pointing in the

same direction (acting like a small magnet) These tiny domains are oriented randomly in the metal

When external fields are applied, energy is required to align these domains in the direction of the main field

These energy losses are called hysteresis losses (core losses) When all the domain have been aligned, the stage is called saturation