Efficient estimation of sensitivities in TLM with dielectric discontinuities

We present two novel approaches for efficient estimation of objective function sensitivities related to dielectric discontinuities with time-domain transmission line modelling. Using only two simulations, of the original and adjoint structures, the sensitivities with respect to all parameters are obtained. The first approach utilizes an approximation of the adjoint problem. It adapts a recent approach that handles perfectly conducting discontinuities. The second approach exploits the analytic dependence of the nodal scattering matrix on the material properties. The adjoint problem is exact for this case. Our approaches are illustrated through examples involving waveguide dielectric discontinuities.