The effect of magnetic shaking on nonoriented silicon steel rings
The effect of magnetic shaking on the incremental permeability of nonoriented silicon steel rings was studied. 50H470 silicon steel is a very popular and cheap material, but does not have a high incremental permeability. However, we achieved a value of 27 000 for the target field of 10 Hz, 0.05 A/m, which is comparable to commercial PC permalloy. We also measured the target field, which ranged from 0.05-5 A/m, 1 Hz-1 kHz. Magnetic shaking was effective at 60 Hz is effective at shaking field amplitudes 40-60 A/m, corresponding to a flux density of 0.2-0.6 B/sub s/. We also made ring samples from 50H470 steel plates produced by a nibbling machine and evaluated the effect of stress on their magnetic properties.
Low‐frequency characteristic of the enhanced incremental permeability by magnetic shaking
In order to analyze the mechanism of magnetic shaking, the permeability and the energy losses for a small amplitude, low‐frequency exciting field are studied under magnetic shaking in comparison with those under the normal condition (without shaking). The permeability and the energy losses were measured for a Metglas 2705M amorphous ribbon wound core by a lock‐in technique in the frequency range of 1–20 Hz under both magnetic shaking (2.7 A/m, 1 kHz) and the normal condition. The effects of the magnetic shaking on the domain wall pinning, the mean wall velocity, and the number of the active walls are described. The strong frequency dependence of the enhanced incremental permeability even at low frequency is explained as a result of these effects.
Magnetic shields
Magnetic shielding is interesting in static fields and in alternating fields up to circa 10kHz. Formulas of the shielding factors for single- and double-walled spherical and cylindrical shells are given, in the latter case also for fields longitudinal to the axes (double-walled shells only for static fields). For cylinders with open ends the shielding factors are represented up to 1kHz for transverse and up to 10kHz for longitudinal fields. In alternating fields interesting resonance effects are observed. Suggestions for practical application are given. Texture materials show an anomalous frequency characteristic of the shielding factor; different models for this effect are discussed. In one of these models the shielding factors of grids are treated.