Adjoint Sensitivity Analysis of Dielectric Discontinuities Using FDTD

We propose an accurate central adjoint variable method (CAVM) for estimating objective function sensitivities related to dielectric discontinuities with structured-grid finite difference time domain (FDTD). Our novel approach features accuracy comparable to that of the central finite difference approximation at the response level. Using only two simulations, of the original and the adjoint EM structures, the sensitivities with respect to all the designable parameters are obtained regardless of their number. Our approach uses the same update equations of the conventional FDTD for the adjoint problem which simplifies the implementation. The proposed technique is extended to evaluate the sensitivities of the S-parameters of multi-port electromagnetic structures. Very good agreement is obtained between our approach and the expensive finite difference approximations.