Practically, there is no such term as absolute “parameters of a magnetic material” because magnetic performance is strongly shape dependent (due to the demagnetizing £eld that causes nonuniformity of magnetization and the change of parameters during the preparation of the sample*). Therefore, when parameters are given, it is recommended to indicate what kind of the sample was used for the investigations (Epstein frame, ring core, sheet, strip, etc.). In such a case, we usually test the average parameters of the whole sample, which is often advantageous because this way we take into account possible heterogeneity of the material.†

It is also possible to determine only the local values of the material parameters (Figure 5.1). So it is also important to take into account the possible heterogeneity of the material. For example, in the case of a grainoriented steel, the performance can differ signi£cantly from grain to grain. Thus, if we use very small sensor, we can determine local parameters of individual grains. If we are interested in average performance, the sensor should be appropriately large to cover signi£cant number of grains (Overshott and Blundell 1984, Moses and Konadu 2001).