The Surface Current node adds a boundary condition for a surface current density Js:

These expressions apply to exterior and interior boundaries respectively. Add a contribution as a Harmonic Perturbation by right-clicking the parent node or clicking Harmonic Perturbation on the Physics toolbar. For more information see Harmonic Perturbation — Exclusive and Contributing Nodes in the COMSOL Multiphysics Reference Manual.

Enter values or expressions for the Surface current density Js0 (SI unit: A/m) coordinates. The defaults are 0 A/m.