Transient application of sub-cell wire and slot models to unstructured, tetrahedral-element meshes

In principle, small features in electromagnetic simulations can be modeled by arbitrary unstructured meshes. In practice, however, the increase in cell count and the reduction in the time step in an explicit algorithm can be prohibitive. Therefore, the ability to model small features using sub-cell models is important. Early work in sub-cell models for thin wires and slots was restricted to simple rectangular-cell grids. Extensions to tetrahedral-element grids are developed in this paper. The algorithms have been implemented into the 3D, transient electromagnetic field solver, VOLMAX. VOLMAX is a fully explicit solver that operates simultaneously on unstructured grids (finite-volume time domain, FVTD) and structured grids (finite-difference time domain, FDTD). VOLMAX is based on an interleaved primary- and dual-grid formulation.