Adjoint variable method for two-dimensional plasmonic structures.

We present, for the first time, an adjoint variable method (AVM) for wideband sensitivity analysis of dispersive materials. The time domain transmission line modeling technique is exploited to calculate the response and its sensitivities with respect to all the designable parameters using at most one extra simulation. A z-domain representation of dispersive materials is utilized in the derivation of this technique. Our approach is illustrated through sensitivity analysis of a two-dimensional teeth-shaped plasmonic resonator. The AVM sensitivities are compared with the accurate and expensive finite difference approach and good agreement is achieved. This theory can be extended to other dispersive materials and dispersive metamaterials as well.