Estimating Reverberant Electromagnetic Fields in Populated Enclosures by Using the Diffusion Model

Abstract

The ability of an enclosure to protect its contents from electromagnetic interference is quantified by its shielding effectiveness. Previous research has proved that the contents of an enclosure may greatly change the internal field and thus the shielding effectiveness. The power balance method is an efficient approach to analyze shielding problems of populated enclosures. One assumption of the power balance method is that in the steady state, the electromagnetic field in an enclosure is homogeneous. In actual circumstances, however, the presence of losses in an enclosure often compromises the field homogeneity and the power balance method may become inaccurate. A diffusion equation approach has been previously proposed to overcome this problem. In this paper, we predict the internal electromagnetic field of a populated enclosure by using the diffusion model, and compare them with the fields obtained by the power balance method, a fullwave electromagnetic solver and measurements, to demonstrate its efficacy. Comparisons between the diffusion model and the power balance method show that for populated enclosures, the internal electromagnetic field varies with position and that the diffusion model allows this to be observed.

Generalized Algorithm Based on Equivalent Circuits for Evaluating Shielding Effectiveness of Electronic Equipment Enclosures

“…The array of staggered apertures in [32] is considered as two separate arrays with doubled vertical distances dv between the apertures. In this case, Zap = Zarr 1 + Zarr 2, where Zarr 1 and Zarr 2 are the impedances of two separate arrays, which are calculated by multiplying ( 16) and (17).…”

“…At the moment, a large number of analytical models for evaluating the SE of enclosures are known. Some of them are based on the power balance [14,15] and diffusion [16,17] equations, others use Bethe's theory of diffraction by small holes [18,19]. However, models based on equivalent circuits are the most widely used.…”

3-D Diffusion Models for Predicting Reverberant Electromagnetic Power Density in Loaded Enclosures

“…Visentin et al argue in [18] that the point source term in (3) gives rise to a spurious "direct" term due to the fact that a diffuse field has not been established in the close vicinity of the point source. This direct term should be removed to give the true reverberant density: (12) In our diffusion model, we disregarded the power density within 50mm (which is about half the mean free path of the cavity) of the point source when considering (12). The details of the enclosure under test and its diffusion model will be presented in Section III and IV respectively.…”

“…All the FreeFEM++ results were obtained in less than 1 minute on a desktop computer (Intel Core i7-870 @2.93GHz, 8GB RAM), compared with up to 42 hours for the full wave model. The energy density and power density in the enclosure are calculated by (12) and (2) respectively.…”

“…In this paper, which is an extended version of our conference paper [12], we present a 3D diffusion model of an enclosure and compare the results to full wave simulations and measurements. The main differences between our study and that in [11] are: first, the enclosure we use contains an aperture, which makes it more realistic; and secondly the measurements were performed YO10 5DD, UK.…”