Magnetic Field Coils for Gradiometer Balancing

We present a design of a compact set of biplanar coils which produces magnetic fields of eight different profiles for the purpose of gradiometer balancing. The magnetic field profiles correspond to uniform magnetic fields in three orthogonal directions and five linearly independent first-order gradients. The coils are made by etching square printed circuit boards that have dimensions of 0.5 m times 0.5 m. The typical inhomogeneity of the magnetic fields and gradients produced by the ideally assembled coil set in a cylindrically shaped volume that measures 50 mm in diameter and 225 mm in height is of the order of 10 ^-5. The coils yield uniform fields and first-order gradients of at least 1(muT/A) and 1(muT/Amiddotm), respectively. The influence of manufacturing tolerances on the performance of the set is investigated by means of Monte Carlo simulations. Based on these simulations, we concluded that the coil set needs to be assembled with a tolerance of 0.1 mm in order to reach a required uniformity of order of 10^-5-10^-4