Some properties and tests of magnetic powders and powder cores

Powders of iron or iron-nickel alloys can be made either mechanically or chemically. The particles are then insulated and pressed into cores; high-permeability cores must be annealed after pressing. The permeability of the core depends mainly on the effectiveness of packing of theparticles. Various systems of expressing the electrical losses are in use: Table 1 gives conversion factors. In laboratory work, bridges and a Q-meter technique can be used to measure the permeability and losses; for control of core production, a permeameter is useful as well as the bridges. Table 4 gives data for various materials, both commercial and experimental, including some ferrites; and Figs. 4 and 5 show that, in typical inductors, the losses in the windings may exceed the losses in the cores.