Understanding the Apparently Poor Conductivity of Galvanized Steel Plates

Abstract

This paper investigates the physical reasons for the apparently poor conductivity of galvanized steel plates (GSP), which has not yet received a proper explanation. Apparent conductivities as low as 0.1 MS/m were reported in the past, which are incongruously low compared to the DC conductivity of steels (4 to 8 MS/m), or zinc (16.7 MS/m), the most common coating agent used against corrosion in steel products. A comprehensive review of results from metallurgy and materials science is presented, providing insights about the multi-layered structure of zinc-based coatings. These are found to be made of a limited set of intermetallic zinc-iron compounds each characterized by a steeply decreasing conductivity as their iron percentage increases. Depending on the galvanization process the relative thickness of these layers can vary widely, explaining the seemingly random apparent conductivity of GSP. Theoretical modeling of these structures shows that their apparent conductivity scales linearly with the frequency, suggesting that it can be far lower than acknowledged so far. An extensive analysis of power-dissipation data from the literature of GSP-based reverberation chambers confirms these predictions, with multiple instances of apparent conductivities as low as 10 kS/m.The conclusion is not that GSP are hopelessly poorly conductive, but rather that care should be taken in selecting the right coating technology, not only based on corrosion protection and minimizing costs, but also in view of its impact on GSP conductivity.

Evaluation of equivalent conductivity of reverberation chambers wall

“…2 and 3 will underestimate the input power used for EMC tests, and therefore lead to the overestimate the performance of the equipment under test. Referring to [10] again, it is found that the conductivity of galvanized steel may be as low as 10 kS/m. However, it is not possible to ensure a good fit for all the frequency range if the conductivity is set to 10 kS/m.…”

“…Otherwise, the numerical Q factor will overestimate the chamber performance, resulting in a low field with respect to the limit level for EMC tests. As discussed in [10,12], the galvanized steel contains a complex ironzinc structure, which cannot be simple regarded as iron or zinc. Moreover, considering the skin depth, it is barely impossible to establish an accurate mathematical model for describing the reflections of incident waves.…”

“…And consequently, the conductivity of the galvanized steel plates cannot be simply set to that of zinc. From the perspective of material properties, the galvanized steel plates show a complex layered structure that may increase the possibility of multiple reflections of incident waves, leading to significantly lower conductivity than zinc [10,11,12,13]. For the simulation or theoretical analysis of RCs, therefore, how to select the appropriate conductivity is always one of the most attractive research topics in RCs.…”