Memory efficient adjoint sensitivity analysis exploiting 3D time domain transmission line modeling

We present a memory efficient implementation of transmission line modeling (TLM)-based adjoint sensitivities. In the original theory, all the transmission line voltage impulses are stored for all the perturbed cells at each time step for both the original and adjoint simulations. This storage can be extensive especially for problems with dielectric discontinuities. We show that only 10% of this storage is required to estimate the adjoint sensitivities with the same accuracy. Our technique exploits a factorization of the scattering matrix that eliminates redundancies in the stored impulses. This technique is illustrated through a three dimensional example that incorporates multiple parameters.