Treatment of metal for the FDTD analysis of terahertz devices

A terahertz stop band filter and a resonator consisting of metal gratings are analyzed using the finite-difference time-domain (FDTD) method, with special attention to the treatment of metal. Numerical results based on a perfect electric conductor (PEC) approximation are compared to those with a metal dispersion being taken into account by the Drude model. It is shown that the results of the resonator for the PEC model are favorably compared with those for the Drude model at frequencies of less than 1 THz. However, care must be taken at higher frequencies, since not only the transmittance at the resonance remarkably reduces for the Drude model, but also its resonance frequency deviates, in comparison with those for the PEC model. Metal mesh structures are also investigated using the periodic FDTD. The differences are found to be relatively small, due to the weak confinement of THz waves in metal mesh structures. The results can serve as a guideline for the FDTD analysis of THz devices consisting of metal.