English: Magnetic field around a Fanselau coil[1] consisting of four round current loops symmetric around their common axis with identical current. This arrangement removes variations in the magnetic field, up to its 5th-order derivative with respect to the center.

The inner loops have an axial position ${\displaystyle z_{1}=\pm 0.29759\,R_{1}}$ and radius ${\displaystyle R_{1}}$. The outer loops have an axial position ${\displaystyle z_{2}=\pm 0.90673\,R_{1}}$ and radius ${\displaystyle R_{2}=0.76322\,R_{1}}$. The current through all loops is ${\displaystyle I}$. The central magnetic field is ${\displaystyle B_{0}=1.23038\mu _{0}I/R_{1}}$.

The dots symbolize where the current flows out of the image plane, whereas the crosses are where the current flows into the plane.