The field sources can be specified in the blocks, at the edges or at the individual vertices of the model. Possible field sources include space, surface and linear electric currents and voltages applied to conductive areas.
A point source in the xy-plane corresponds to a linear current in out-of-plane direction. In axisymmetric case the point source represents the current in a thin ring around the axis of symmetry. Edge-bound source in the plane of model represents a surface current in three-dimensional world. It is specified by the Neumann boundary conditions for the edge.
There are several ways to specify space-distributed electric current. In a massive conductor, you can specify either a total current or a voltage applied to the conductor. In planar problems, voltage drop is specified per unit depth of the model, and in axisymmetric case voltage is assumed per one turn around the axis of symmetry. Nonzero voltage applied to a conductor in axisymmetric problem means that the conductor has a radial cut, and the voltage is applied to sides of the cut. In practice this option could be used to describe known voltage applied to massive spiral wiring, in which case the total voltage drop for the coil should be divided by number of turns in the coil.
Several blocks with the same value of total current or voltage applied can be considered as connected in series. In that case each conductor carries the same total current, and voltage (if any) is applied to the terminals of the whole group of conductors connected in series.
Note. The meanings of zero total current and zero voltage applied to a conductor are very different. Zero voltage means that the conductor's ends are short circuit, and zero value of the total current means open ends of the conductor.
Field source could also be specified in non-conductive areas. This option is useful to specify current in coils made of thin wire, where skin effect is insignificant. You can specify either a total current or a current density, whichever is easier to calculate in a specific case. Current density in a coil can be obtained from the equation
j = n·I / S,
where n is a number of turns, I is a total current, and S is a cross-sectional area of the coil.
Note. In order to properly model thin wire coils, the source current density j0 in non-conductive areas is assumed to be uniform in both plane and axisymmetric cases. Its behavior is different for massive conductors, where source current density varies as 1/r in axisymmetric case.