Accurate Treatment of Nonconformal Material Interfaces in the Finite Integration Technique

We discuss a generalized strategy to model material interfaces in the finite integration technique (FIT) on Cartesian meshes. It originates from the exact formula for the ratio of grid fluxes and grid voltages, which requires a priori knowledge of the local fields. For axis-parallel material interfaces, this field information is canceled out, yielding the standard expressions of the FIT's material operators. For nonconformal interfaces, two concepts are discussed to obtain feasible implementations. Applied to an exemplary quasistatic example, the generalized formula shows superior accuracy compared with staircase approximations.