Power Dissipation in Reverberation Chamber Metallic Surfaces Based on Ferrous Materials

Abstract

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 quality factor, Qw, 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 dB. 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 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 Qw over the GHz range, as opposed to a squareroot 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.

Assessment of Broadband Shielding Effectiveness of Composite Panels for Protective Enclosures

“…For both enclosures with the Al cover, the numerical model shows a good agreement with the experimental result from 100 Hz to 30 kHz, before observing some variations in the experimental measurements. However, for the steel cover, the numerical result is significantly higher than the experimental one for the two following reasons detailed in [27]. First, permeability exhibits an imaginary part that is not considered in our simulations and leads to magnetic losses, which are hard to assess in the microwave range.…”

“…Its influence is not included in our simulations as its thickness is not known. As explained in [27], the distribution of the induced currents in the different layers is a function of frequency. From Fig.…”

Understanding the Apparently Poor Conductivity of Galvanized Steel Plates

“…Normal incidence through all internal layers is assumed, as argued in Section III-A. Surge reflectivity Γ i at each internal interface (i < 4) can be computed as in (9), substituting the contrast ratio σ i+1 /σ i under the square root. The bulk DC conductivities are used instead of the effective bulk ones, since none of the ZnFe compounds presents any significant magnetic behavior (cf.…”

“…should span a multi-octave bandwidth, in order to provide evidence of the transition region; this excludes results from millimeter-wave tests and wireless device tests, since they are narrow-band. References [9], [67]- [85] meet these criteria and provide the basis for the analysis in Section IV-C.…”

“…A poor surface conductivity has an especially strong impact in closed environments [5], where electromagnetic waves interact multiple times with metal surfaces, and in particular test facilities such as reverberation chambers (RC), which strongly rely on long reverberation times to build up high-strength fields for electromagnetic compatibility tests [6], [7]. Galvanized steel plates (GSP) used in typical RC are also zinc coated, but empirical results can be explained only by assuming that their surface conductivity be considerably lower than 1 MS/m [8], [9]. In all these previous empirical observations, no physical justification was advanced as to why GSP present such a low conductivity.…”