The Magnetic Field boundary condition

specifies the tangential component of the magnetic field. As the equation suggests, the boundary condition only guarantees that the tangential components of H and H0 are equal. Their normal components might deviate depending on specific situations.

The Harmonic Perturbation subnode (it is of the exclusive type) is available from the context menu (right-click the parent node) or on the Physics toolbar, click the Attributes menu and select Harmonic Perturbation. For more information see Harmonic Perturbation — Exclusive and Contributing Nodes in the COMSOL Multiphysics Reference Manual.

Enter the value or expression for the components of the Magnetic field H0 (SI unit: A/m). The defaults are 0 A/m.