Power Dissipation in Reverberation Chamber Metallic Surfaces Based on Ferrous Materials

Models predicting the composite quality factor (QF) of a reverberation chamber (RC) consider, among several potential contributors, dissipation in its metallic boundaries. The related partial QF, Q
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, is of fundamental importance, as it controls the asymptotic high-frequency behavior of an RC and, ultimately, its ability to generate high-intensity fields. Yet, the current model has been known to overestimate in certain cases the composite QF by up to several decibel. This paper provides insight into the causes of these disagreements by introducing generalized models of dissipation in ferrous materials found in RCs, by first acknowledging that their magnetic permeabilities are complex quantities, which is shown to theoretically boost dissipation well beyond the gigahertz (GHz) range. A more general dissipation model is presented, taking into account the layered nature of steel plates. Among its predictions, confirmed by experiments, are extra losses from steel surfaces in the lower frequency range and the linear increase in Q
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over the GHz range, as opposed to a square-root dependence expected for homogeneous bulk metals. Metallic coating layers, originally introduced to protect steel plates, have therefore a more fundamental role to play, controlling dissipation levels by reducing interactions with ferrous materials and should therefore be designed accordingly.