Permeability and Saturation of Iron

Author: E.E. Kimberly

Fig. 7-3. Magnetization Curve of Iron

The permeability of a vacuum, air, or any one of many other media is a constant, regardless of the flux density in it. The permeability of iron, nickel, cobalt, or any one of several of their alloys is a variable function of the flux density in it. Fig. 7-3 is a typical magnetization curve of flux density B in iron plotted against H

Which, from equation (7-1), is

each centimeter of length. For convenience, the magnetization curves for commercial iron are usually given as gausses plotted against ampere-turns per centimeter of length of path. Beyond the point a, Fig. 7-3, called the knee of the curve, the increase in B for a given increase in H becomes very small. It is quite possible, but seldom practicable, to carry the magnetization beyond the point b.

In calculating the number of ampere-turns required to magnetize a piece of iron to a certain flux density, the permeability of the iron at that flux density must be known, or a curve of NI per unit length of path plotted against flux density must be available for the specific magnetic material being used.