An analytical formulation has been developed for the shielding effectiveness of a rectangular enclosure with an aperture. Both the magnetic and electric shielding may be calculated as a function of frequency, enclosure dimensions, aperture dimensions and position within the enclosure. Theoretical values of shielding effectiveness are in good agreement with measurements. The theory has been extended to account for circular apertures, multiple apertures, and the effect of the enclosure contents.

This paper presents an intermediate level circuit model (ILCM) for the prediction of the shielding effectiveness (SE) of a rectangular box containing a rectangular aperture, irradiated by a plane wave. The ILCM takes into account multiple waveguide modes, and is thus suitable for use at high frequencies and/or relatively large boxes. Inter-mode coupling and reradiation from the aperture are taken into account. The aperture may be positioned anywhere in the front face of the box, and the SE at any point within the box may be found. The model is presented in such a way that existing ILCM techniques for modelling elements such as monopoles, dipoles, loops, or transmission lines may be seamlessly incorporated into the circuit model. Solution times using the ILCM technique are three orders of magnitude less than those required by traditional numerical methods such as FDTD, TLM, or MoM. Accuracy however is not significantly compromised. Comparing the circuit model with TLM over nine data sets from 4 MHz to 3 GHz resulted in an rms difference of 7.70 dB and mean absolute difference of 5.55 dB in the predicted SE values.

The inclusion of thin lossy material layers, such as carbon-based composites, is essential for many practical applications for modeling the propagation of electromagnetic energy through composite structures such as those found in vehicles and electronic equipment enclosures. Many existing schemes suffer problems of late time instability, inaccuracy at low frequency (LF), and/or large computational costs. This paper presents a novel technique for the modeling of thin-layer lossy materials in finite-difference time domain (FDTD) schemes, which overcomes the instability problem at low computational cost. For this, a 1-D subgrid is used for the spatial discretization of the thin-layer material. To overcome the additional time-step constraint posed by the reduction in the spatial cell size, a Crank-Nicolson time-integration scheme is used locally in the subgridded zone, and hybridized with the usual 3-D Yee-FDTD method, which is used for the rest of the computational domain. Several numerical experiments demonstrating the accuracy of this approach are shown and discussed. Results comparing the proposed technique with classical alternatives based on impedance boundary condition approaches are also presented. The new technique is shown to have better accuracy at LFs and late time stability than existing techniques with low computational cost.

This paper examines the coupling between two arbitrarily positioned wire segments inside a rectangular enclosure. The enclosure is treated as a superposition of analogous transmission lines which have been short circuited at two positions on the propagation axis. Each analogous transmission line is associated with a particular waveguide mode in the cavity. Previous work has used this analogy to predict the coupling between two monopoles inside a small box using the dominant TE/sub 10/ mode. This paper considers the general case of high-frequency coupling between two wire monopoles in a large rectangular cavity, where several higher order modes are active. By taking into account higher order modes, and the mutual coupling between the modes, a simple equivalent circuit is presented which can give a prediction for the coupling between the monopoles. Experimental results for various monopole pair positions are shown, which indicate the success of the multimode theory. The technique requires far less computer resources than traditional methods for solving such a problem (e.g., MoM, TLM or FDTD), with solution times of less than a second on an average PC. In addition, considerable insight into the coupling process can be gained by including or excluding particular waveguide modes. This is not possible with numerical methods.

Absorption by the contents of an equipment enclosure, particularly printed circuit boards (PCBs), affect the enclosure's shielding performance. At high frequencies, this absorption can be quantified using the angle of arrival and polarization averaged absorption cross-section (ACS). However, there is no available data on the high-frequency absorption characteristics of modern PCBs. In this study, we apply a reverberation chamber to the determination of the average ACS of a large number of PCBs taken from contemporary information and communication technology (ICT) equipment to provide a unique and comprehensive dataset. The ACS was found to range from 4 × 10 ^-4 -10 ^-2 m ² from 2-20 GHz and different classes of PCB could be identified according to their surface characteristics. The “shadowing effect” of densely packed PCBs was also quantified for a subset of the PCBs. It was found that the ACS of a PCB in the stack was reduced by 20%-40% compared to its value when isolated. By way of a review of the general power balance analysis of an electrically large populated equipment enclosure in an external environment, we show how the acquired data will be useful for future qualification methodologies for ICT enclosures and PCBs.

The finite-difference time-domain (FDTD) method is a numerical technique that is widely used to solve Maxwell's differential equations in the time domain [1]. Both space and time are discretized. Space is discretized into rectangular-shaped elements in two-dimensional (2-D) or cuboid elements in three-dimensional (3-D). Cuboid elements, where the electric fields are located on the edges of the cuboid and the magnetic fields are normal to the faces, are called Yee cells and are the fundamental elements of most FDTD methods [2]. By filling up the problem space with these cells, we obtain a 3-D mesh, where neighboring cells share edges and faces. Each cell has three associated electric and magnetic field components, while the other field components belong to adjacent cells. The properties of each cell are adjusted to represent materials such as dielectrics or conductors by adjusting the constitutive parameters used in the field equations in the corresponding cells, hence forming the geometrical structure of the problem to be solved. For example, Figure 1 shows a sphere and a version of the sphere discretized using cubic elements.