Modeling and design of shielding enclosures for EMI mitigation: Experiments, and finite-difference time-domain and method of moments modeling

Electromagnetic interference (EMI) problems associated with shielding enclosure designs are studied herein. EMI from slots and apertures resulting from the coupling of interior sources through enclosure cavity modes is investigated experimentally and numerically using the finite-difference time-domain (FDTD) method, and the results indicate that radiation at cavity mode resonances through slots and apertures of non-resonant dimensions can be as significant as the radiation at aperture or slot resonances. EMI through aperture arrays for airflow in shielding enclosures resulting from coupling of interior sources is also investigated numerically, and experimentally. Mutual coupling between apertures or slots in airflow arrays is also studied numerically by means of the method of moments (MoM). Justification for a simple empirical design approach for the relation between the number N and size a of apertures, and the shielding effectiveness ∼Na3 of an airflow aperture array is given.; A relatively simple, closed-form expression has been developed to estimate the EMI from perforated shielding enclosures excited by interior sources through enclosure cavity modes. A power balance method, Bethe's small hole theory, and empirical formulae for the relation between radiation and slot length and number of slots, were employed to calculate the far-field radiation from shielding enclosures. Comparisons between measurements and estimated field strengths agreed within engineering accuracy. The estimate is presently most useful for comparing the EMI levels from different enclosure design options.; The measurements and numerical modeling (FDTD and MoM) generally agree well throughout the investigations, and demonstrate the usefulness of numerical modeling for investigating aspects of shielding enclosure design such as coupling to slots and apertures, and slot or aperture interactions.