Hybrid model for estimating the shielding effectiveness of metallic enclosures with arbitrary apertures
Electronic enclosures often require ventilation and electromagnetic shielding, which have conflicting design requirements. This study proposes a hybrid model, based on circuit model and full-wave method, for estimating the shielding effectiveness of empty metallic enclosures with ventilation apertures of arbitrary shape or aperture arrays of arbitrary distribution on one side of the enclosures. Such perforated enclosures are split into a perforated plate and semi-enclosed waveguide that is shorted at the end. The S parameters of the perforated plate are calculated by a full-wave method and used to estimate the aperture impedance. An equivalent circuit model of a perforated enclosure is established, considering arbitrarily-positioned apertures, arbitrarily-chosen observation points, and higher-order modes. A modified plane wave decomposition technique is adopted to solve the problem of plane waves with arbitrary incident and polarisation directions. In particular, the effects of the electric field components perpendicular to the perforated plate are considered. The efficiency and accuracy of the hybrid model are evaluated by the transmission line matrix method, finite integration technique, experimental observations and existing circuit models. The hybrid model requires much less simulation time than pure full-wave methods such as the transmission line matrix method.
