Novel Compensated Moment Detection Coil

We constructed a coil system providing a homogeneity of the sixth order and a compensation of the second order to measure the magnetic dipole moment. The coil system consists of six circular filaments connected in series; two of them are connected with the other four in opposition. This coil system is highly insensitive to external magnetic disturbances, even if they are inhomogeneous, whereas its sensitivity inside the coil is constant over a large part of its volume. In this paper, we report our optimization calculation for the system, calculation of the performance, and measurement results. We measured the influence of a magnet and of an iron plate close to the coil on the magnetic dipole moment for the coil system and also for a pair of Helmholtz coils and compared the results with the calculated values. By reason of the principle of inversion, the coil system can also be used as a field-generating coil, where the decay of the field strength outside the system is much more rapid than for noncompensated systems.