Stable modelling of arbitrary thin slots in the finite‐element time‐domain method

A subcell model for arbitrarily located thin wires in the finite‐element time‐domain (FETD) method using modified telegraphers equations has been developed by Edelvik et al . Recently a dual set of equations has been proposed for modelling of thin slots. In this paper, we show that using a similar algorithm as for thin wires we can take thin slots of arbitrary location into account. Previous thin slot models have been susceptible for instabilities. We prove that a symmetric coupling between field and slot yields a stable time‐continuous field–slot system and that the fully discrete field–slot system is unconditionally stable. The proposed method is demonstrated for scattering from straight and circular slots in an infinite conducting wall and for calculating the power delivered to a shielding enclosure including a slot. The results are in good agreement with published experimental data.