Magnetization curves

The development of Remote Field Eddy Current probes requires experience and expensive experiments. The numerical simulation of electromagnetic fields can be used not only for a better understanding of the Remote Field effect but also for the probe lay out. Geometrical parameters of the prohe can be derived from calculation results as well as inspection parameters. An important requirement for a realistic prediction of the probe performance is the consideration of material properties of the tube for which the probe is designed. The experimental determination of magnetization curves is necessary and can be satisfactory done with a simple experimental setup. 

The permeabiHty = B jH is important information for soft magnetic materials. The most often quoted values ate the initial permeabiHty and the maximum permeabiHty ]1. These correspond to the initial and maximum slopes of the virgin magnetization curve, respectively (Fig. 1). Because the value of at S/H = 0 needs to be extrapolated from measurements at finite H, the value often is quoted ia commercial catalogues at specific B or H The quoted values usually are relative to the free-space value p.Q. 

Fig. 2. Magnetization curves of commercial soft magnetic materials.

Figure 1.10 Hysteresis loop and magnetizing curve illustrating hysteresis loss...

This is the point on the magnetic curve of the laminated core of the CT at which the saturation of the core will start. It is defined as the point where an increase of 10% in the secondary voltage will increase the excitation current / i by 50% (Figure 15.19). Beyond this point, a very large amount of primary current would be required to further magnetize the core, thus limiting the secondary output to a required level. 

Actually the design of the dc EMI filter inductor is an easy matter. The core manufacturer provides a graph entitled Normal Magnetization Curves for the MPP cores, as seen in Figure 3-22. A permeability of 60 or below is recommended. 

Fig. 15 Magnetization curves for paramagnetic species with various J = 5-values. These data represent a landmark in that the magnetization of a hydrocarbon molecule [15 m = 4] surpassed for the first time those of transition-metal and lanthanide ions, represented here by NH4Fe(S04)2-12Hj0 and Gd2(S04)3-8H20, respectively.

Fig. 14. Magnetization curves of reconstituted horse spleen ferritin. The solid lines are fits to expression (14). Reproduced with permission from Ref (35).

The first type is the crystal anisotropy which is responsible for the dependence of the magnetization curves on the orientation of the crystal in the magnetic field. The energy E, which is necessary to deflect the magnetic moment in a single crystal from the easy direction into less easy ones is given for cubic crystals by ... 

Fig. 7.11 Room temperature specific magnetization curves of magnetite, maghemite, hematite, goethite, and ferrihydrite (from Coey, 1988, with permission).

Difficulties arise, however, in mixtures and the magnetization curves will then depend on the proportions of the various oxides, including the antiferromagnetic ones (hematite, goethite) and on the crystal type (SD, MD). Positive identification is then only possible with the help of other methods, such as XRD (see for example Resende et al., 1986 Allan et al., 1988). 

Figure 6.9 Properties of superconductors (a) resistivity-temperature curve for a pure (solid) and an impure (broken) superconductor (b) magnetization as a function of external field for type I superconductor (c) magnetization curve for a type II superconductor.

K is noteworthy (Allemand et al., 1991). Cgo TDAE is a soft ferromagnet and is a low-dimensional (possibly Heisenberg) system (Rao Seshadri, 1994). It does not show remnance in the magnetization curve. 

---