Sensitivity and spatial resolution of square loop SQUID magnetometers

We calculate the flux threading the pick-up coil of a square SQUID magnetometer in the presence of a current dipole source. The result reproduces that of a circle coil magnetometer calculated by Wikswo with only small differences. However it has a simpler form so that it is possible to derive from it closed form expressions for the current dipole sensitivity and the spatial resolution. The results are useful to assess the overall performance of the device and to compare different designs.