Modified Explicit Finite-Difference Time-Domain Method for Nonparaxial Wave Scattering From Electromagnetic Metasurfaces

An updated method for simulating the scattered fields from a dispersive Huygens' metasurface using the explicit finite-difference time-domain technique has been proposed and numerically demonstrated. The method uses a spatial-temporal averaging of the electric and magnetic fields, using virtual sources in a standard Yee cell grid. This creates a nonparaxial implementation of the generalized sheet transition conditions in the time domain and rigorously solves the scattered fields in reflection and transmission regions separately. The metasurfaces are solved for Lorentzian susceptibilities, and the proposed method is successfully demonstrated using two examples: a uniform metasurface with a strongly divergent beam and a space-modulated metasurface emulating a diffraction grating.