Effect of magnetic anisotropy on magnetic shaking

The effect of magnetic shaking on both the transverse and axial shielding factors ~TSF and ASF! is investigated using open-ended cylindrical shields made of Metglas 2705M amorphous ribbons. Shaking enhancement is found to be strongly dependent on the orientation of the magnetic anisotropy of the shielding material, that is, the anisotropy axis should be aligned along the corresponding shielding direction to achieve a greater enhancement of the TSF or ASF. Magnetic shaking provides an ;40-fold increase in the TSF and only an ;twofold increase in the ASF for a shield consisting of a helical structure of the ribbons. The situation is almost completely different if the ribbons’ structure is axial: ;twofold increase in the TSF and ;20-fold increase in the ASF. The shaking field intensity ~;320 mOe at 1 kHz! for axial shielding is found to be about 10 times larger than that for transverse shielding. Experiments with a three-shell axial structure shield show an ;350-fold increase in the ASF ~;40 000, which is one order larger than that of similar conventional shields!. The TSF of this shield is, however, about one tenth of its ASF. Reorientation of the ribbons in the innermost shell, from an axial structure to a helical one, increases the total TSF ~;50 000! while still maintaining a large ASF ~;20 000!. Hence, combining shells of helical and axial structures and having a proper distribution of the shielding material between them may allow the construction of an open shield with a large ~.20 000! total ASF and TSF. © 1999 American Institute of Physics. @S0021-8979~99!55608-9#