MS3p allows the specification of a uniform volumetric current density that either flows in a particular Cartesian direction, or in a circular arc. This excitation is called a Coil in Analyst. Care should be taken to ensure that use of the excitation does not require a source/sink in open space inside the model. In other words, no volumetric current source should terminate inside the model. Current can flow in a loop, or can come in/exit from a boundary. Current should enter/exit only through Neumann boundary condition surfaces (which allow tangential magnetic field), and the current direction should align with the surface normal at the entry/exit point.