Figure of merit and spatial resolution of superconducting flux transformers

A figure of merit relating the magnetic field in one point of space and the output of a superconducting magnetometer system is introduced. This new figure of merit can be understood as the magnetic field gain provided by a flux transformer. By its definition the gain also takes into account the spatial variation of the magnetic field, i.e., its source. Therefore, the gain is a suitable parameter for the optimization of a flux transformer for measuring fields from given sources. As another topic the spatial resolving power of a flux transformer is studied. A simple discrimination criterion gives the result that two magnetic field sources cannot be resolved even with a point vector magnetometer if the separation of the sources is below a threshold value. A second-order flux transformer optimized with respect to gain and resolving power is finally presented.