The Material Discontinuity node, found under the Interior Conditions submenu, adds an interior boundary condition to handle jumps in material properties. As the interface is based on the discontinuous Galerkin method special handling is necessary when a jump exists in the specific characteristic impedance Z0 = ρc of the medium.

Subscripts “up” and “down” in the equation refer to the up and down sides of the interior boundary, relative to the normal n.