Research in Electromagnetic Shielding Theory. Part 1. Shielding by Rectangular Enclosures

摘要

General expressions for the electric and magnetic fields at any point inside slotted and continuous, rectangular enclosures exposed to arbitrary external, time harmonic source fields are obtained under the assumption that the enclosures are constructed from good conductors and the slot is small compared to the wavelength of the source field. These expressions consist of infinite series summed over the TE waveguide modes where each term is the product of one or more mode functions and a Fourier coefficient that depends on the spatial variation of the source magnetic field. The Fourier coefficients were evaluated in closed form for two cases: the outside surface of the slot exposed to a spatially uniform magnetic field and the outside surface of one wall of the continuous enclosure exposed to a spatially uniform magnetic field. Frequency domain calculations based on these expressions showed that for frequencies below the enclosure cutoff frequency, the magnetic field at all locations inside a typical slotted enclosure is independent of frequency. For the same range of frequencies the field inside a continuous enclosure is a monotonically decreasing function of frequency. At frequencies above cutoff, the fields in both slotted and continuous enclosures show very complex behavior associated with cavity resonances.