Efficient time-domain sensitivity analysis using coarse grids

We propose an efficient coarse-grid approach to the sensitivity analysis with full-wave electromagnetic (EM) time-domain simulations. In order to compute the response sensitivity using an adjoint approach, waveforms at all perturbation grid points need to be saved and post-processed. Therefore, the memory requirements of the response sensitivity analysis may become excessive for electrically large objects or problems with a large number of optimizable parameters. The use of coarse grids can reduce these memory requirements drastically and improve the computational efficiency of the sensitivity analysis while maintaining good accuracy. In this paper, we show that the discretization step size used in the sensitivity computation can be many times larger than the step size used in the finite-difference time-domain (FDTD) simulation. The effects of the coarseness of the grid on the accuracy of the sensitivity analysis are investigated. Verification is carried out through 1-D, 2-D and 3-D lossy dielectric structures using commercial FDTD solvers.