Central-Node Approach for Accurate Self-Adjoint Sensitivity Analysis of Dielectric Structures

The field solution at the perturbation grid points is needed to perform sensitivity analysis usingadjoint approaches. On the other hand, the field solutions provided by time-domainsolvers are the least accurate at dielectricinterfaces, especially in the caseof significant losses. These interfaces are the places where some or all perturbation grid points reside. We propose acentral-node approach for the case of dielectric mediums with or without loss. The accuracy of this approach is one orderhigher than that of ouroriginal adjoint approach in the case of dielectric discontinuities, while the computational efficiency remains the same. Verification is carried out through examples using commercial finite-difference difference time-domain solvers.