Evaluation of the diffusion equation for modeling reverberant electromagnetic fields

Determination of the distribution of electromagnetic energy inside electrically large enclosed spaces is important in many electromagnetic compatibility applications, such as certification of aircraft and equipment shielding enclosures. The field inside such enclosed environments contains a dominant diffuse component due to multiple randomizing reflections from the enclosing surfaces. The power balance technique has been widely applied to the analysis of such problems; however, it is unable to account for the inhomogeneities in the field that arise when the absorption in the walls and contents of the enclosure is significant. In this paper we show how a diffusion equation approach can be applied to modeling diffuse electromagnetic fields and evaluate its potential for use in electromagnetic compatibility applications. Two canonical examples were investigated: A loaded cavity and two cavities coupled by a large aperture. The predictions of the diffusion model were compared to measurement data and found to be in good agreement. The diffusion model has a very low computational cost compared to other applicable techniques, such as full-wave simulation and ray-tracing, offering the potential for a radical increase in the efficiency of the solution high frequency electromagnetic shielding problems with complex topologies.