The BH Magnetization Curve (Figure 27) shows how much flux density (B) results from increasing the flux intensity (H). The curves in Figure 27 are for two types of soft iron cores plotted for typical values. The curve for soft iron 1 shows that flux density B increases rapidly with an increase in flux intensity H, before the core saturates, or develops a "knee." Thereafter, an increase in flux intensity H has little or no effect on flux density B. Soft iron 2 needs a much larger increase in flux intensity H before it reaches its saturation level at H = 5000 At/m, B = 0.3 T.

Air, which is nonmagnetic, has a very low BH profile, as shown in Figure 27.

Figure 27 Typical BH Curve for Two Types of Soft Iron

The permeability () of a magnetic material is the ratio of B to H. Equation (1-18) is the mathematical representation for magnetic material permeability.

The average value of permeability is measured where the saturation point, or knee, is first established. Figure 27 shows that the normal or average permeability for the two irons as follows.

In SI units, the permeability of a vacuum is or T-m/At. In order to calculate permeability, the value of relative permeability V_t. must be multiplied by loo. Equation (1-18) is the mathematical representation for permeability.

Example: Find the permeability of a material that has a relative permeability of 100.