The Fluxball A Test Coil for Point Measurements of Inhomogeneous Magnetic Fields

Abstract

The value of a magnetic field at a point is equal to the volume average of the field over the interior of any sphere centered at the point and not containing any sources of the field. It is therefore possible to wind a coil on the surface of a sphere in such a way that the flux through the coil is proportional to the field at a point even though the field varies over the region occupied by the coil. By combining concentric windings of this type one obtains a solid spherical winding equivalent to a series of coaxial cylindrical windings of different lengths but of equal and constant axial turn spacing, and therefore not difficult to wind. Design formulas are derived and construction procedures described.