TY - JOUR
T1 - Coil geometry for efficient active compensation with separated magnetic shields
AU - Nakashima, Yoshihiro
AU - Sasada, Ichiro
N1 - Funding Information:
We would like to thank Mr. Takashi Yamaguchi for his helpful discussions. This work is supported by the Grant-in-Aid for Scientific Research (A) and Grant-in-Aid for JSPS Fellows from Japan Society for the Promotion of Science. Table I. Comparison of compensation currents. Position of the coil FEM (dc, 10 Hz) Experiment θ = 45 ° 6.7 A turns 8.2 A turns θ = 60 ° 5.1 A turns 6.3 A turns θ = 80 ° 4.1 A turns 4.7 A turns Middle 3.4 A turns 3.9 A turns Edge 2.7 A turns 3.0 A turns FIG. 1. Cross-sectional view of the magnetic shell and positions of coil conductors (small circles) used in the FEM analysis. The Neumann boundary condition is set on the x -axis whereas Dirichlet boundary condition on the y -axis. r = 12 cm , θ = 45 ° , 60°, and 80°, Middle = ( 17 , 6.5 ) , Edge = ( 22 , 6.5 ) FIG. 2. Distribution of attenuated magnetic fields (FEM) inside the shield along the x -axis. 0 cm is the center and 20 cm is the end of the flange. (a) dc magnetic field. (b) ac magnetic field (10 Hz). Broken lines in (b) show results without phase adjustment, in which the phase of the compensation current is simply inverted 180° from that generates B y o . FIG. 3. Distribution of the attenuated magnetic field. (Experiment.) FIG. 4. Compensation magnetic fields depicted by flux lines for two different saddle coils, where 6.7 A currents is used in (a) and 2.7 A in (b). Very similar magnetic field are generated inside the magnetic shells (only upper part is shown) FIG. 5. Phase delays vs frequency for two different magnetic fields; uniform magnetic field and compensation magnetic field. Difference in the phase delay between two cases is fairly small, for example, about 1° angle at 10 Hz.
PY - 2009
Y1 - 2009
N2 - We have already proposed a new method of magnetic shielding aiming for magnetocardiography, in which magnetic shells are separated and a new compensation scheme is employed to allow for wide space between them. Each magnetic shell that consists of a half of the cylinder (diameter=20 cm and length=60 cm) and two flanges at both ends of the half cylinder extending along the radial direction has a saddle coil on its outer surface with the coil's long straight section running parallel to the axis of the cylinder. In this paper, the relationship between the width of the long straight sections of the saddle coil and the efficiency of the active compensation is investigated by the finite element method (FEM) analysis and by experiments. A magnetic shield used in this study is a double shell structure where each shell is made of stacked amorphous tapes and the outer shell has a magnetic shaking coil for the enhancement of the permeability. We have found that for a given magnetic field, the compensation current necessary for a given magnetic field varies by a factor of 3 depending on the width of a saddle coil and that its value monotonically decreases with increasing the width. We have also confirmed that the phase delay of the compensation magnetic field experienced while it comes in the magnetic shell is small.
AB - We have already proposed a new method of magnetic shielding aiming for magnetocardiography, in which magnetic shells are separated and a new compensation scheme is employed to allow for wide space between them. Each magnetic shell that consists of a half of the cylinder (diameter=20 cm and length=60 cm) and two flanges at both ends of the half cylinder extending along the radial direction has a saddle coil on its outer surface with the coil's long straight section running parallel to the axis of the cylinder. In this paper, the relationship between the width of the long straight sections of the saddle coil and the efficiency of the active compensation is investigated by the finite element method (FEM) analysis and by experiments. A magnetic shield used in this study is a double shell structure where each shell is made of stacked amorphous tapes and the outer shell has a magnetic shaking coil for the enhancement of the permeability. We have found that for a given magnetic field, the compensation current necessary for a given magnetic field varies by a factor of 3 depending on the width of a saddle coil and that its value monotonically decreases with increasing the width. We have also confirmed that the phase delay of the compensation magnetic field experienced while it comes in the magnetic shell is small.
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U2 - 10.1063/1.3086291
DO - 10.1063/1.3086291
M3 - Article
AN - SCOPUS:65249138128
SN - 0021-8979
VL - 105
JO - Journal of Applied Physics
JF - Journal of Applied Physics
IS - 7
M1 - 07A336
ER -