Today I’ve just been playing with my software to render this 3D animation of the magnetic field generated by a Helmholtz coil. The objective was to observe how the magnetic homogeneity varies with respect to the distance between coils.
As you can see, we find the maximum homogeneity when the distance between coils equals the radius (70mm). The total central magnetic field is also decreasing as the coils spread apart. In each of the 300 simulations to generate this animation, the central magnetic field is calculated and plotted to the left graph, and then only the 3D vectors fitting the 100ppm volume are shown. The homogeneity is also plotted below the central magnetic field graph, and the maximum variability shown in the right color scale in nT.
Enjoy!