Wideband FDTD-Based Adjoint Sensitivity Analysis of Dispersive Electromagnetic Structures

We propose a wideband adjoint variable method for sensitivity analysis of dispersive structures utilizing finite difference time domain (FDTD). Using only one extra FDTD simulation, the sensitivities of the desired response are estimated over the frequency band of interest with respect to all the design parameters. The presented theory is based on direct discretization of Maxwell's equations. We derive the equations of the adjoint system for problems with different types of dispersion profiles including the Lorentz, Drude, and Debye models. The validation of our approaches is done through comparison with the expensive finite-difference approach applied at the response level.