Design of a Single-Ring Mechanically Tunable Halbach Cylinder

Halbach cylinders are arrays of magnets configured radially such that the superposition of the remnant magnetic fields creates a strong and uniform field. The characteristics of the magnetic field and compact nature of their design has led to applications in low-field magnetic resonance imaging. Herein, we report on the fabrication of a single-ring, mechanically tunable Halbach cylinder designed to modulate the magnetic field within the open bore volume. The polarization directions of the magnets are dynamically controlled via a mechanical gearing mechanism. A cylindrical array of twelve $1.00 \times 1.00 \times 4.00 \mathrm{in}^{3}$ neodymium bar magnets was assembled with the 4 in dimension directed along the bore axis producing an open bore of 7 in in diameter. Finite Element Method Magnetics (FEMM) software was used to simulate the Halbach cylinder in three magnet configurations representing weakest to strongest bore magnetic field.