• Corpus ID: 219303589

Designing Coils to Produce User-specified Magnetic Field Profiles Inside a Closed Finite-length High-Permeability Cylinder

@article{Packer2020DesigningCT,
  title={Designing Coils to Produce User-specified Magnetic Field Profiles Inside a Closed Finite-length High-Permeability Cylinder},
  author={M. Packer and P. J. Hobson and Niall Holmes and James Leggett and Paul Glover and Matthew J. Brookes and Richard Bowtell and T. Mark Fromhold},
  journal={arXiv: Applied Physics},
  year={2020}
}

• M. Packer, P. J. Hobson, +5 authors T. Fromhold
• Published 4 June 2020
• Physics
• arXiv: Applied Physics

Commercially available passive magnetic shields with active components that allow the generation of a tailored low-field environment are required for many applications in science, engineering, and medical imaging. Until now, accurate field nulling, or field generation, has only been possible over a small fraction of the overall volume of the shield. This is due to the interaction between the active field-generating components and the surrounding high-permeability passive shielding material. Such material distorts the field generated by the active parts, making it hard to optimize the spatial variation of the field ab initio. Here, we show that this design problem can be overcome for cylindrical shields with planar end-caps by explicitly including the interactions with the passive shielding layers in the optimization procedure for the active field-generating components. We modify the Green's function for the magnetic vector potential so that it satisfies the boundary conditions of the passive shield, and then apply a harmonic minimization method. We design two hybrid active--passive systems inside a closed cylindrical perfect magnetic conductor, which generate a constant transverse field, $B_x$, across the cylinder, and a linear transverse field gradient, $\mathbf{B}=(z~\mathbf{\hat{x}}+x~\mathbf{\hat{z}})$, along the axis of the cylinder. The fields generated by both the constant transverse and linear gradient systems are within $0.1\%$ and $0.5\%$ of the desired target field, respectively, over $40\%$ of the central radial and axial extent of a simulated passive magnetic shield. Our optimization procedure can be adapted to design active--passive systems that generate any user-specified static magnetic field in the interior of a closed cylindrical shield of any length, enabling the development and miniaturization of systems that require accurate magnetic shielding and control.