On the Shielding Effectiveness Calculation of Enclosures Through Measurements in Reverberation Chambers

Abstract

The IEC 61000-4-21 and IEEE 299.1 documents report similar but not equal procedures to measure the shielding effectiveness (SE) of enclosures through the use of Reverberation Chambers (RCs). In this paper, it is shown that these two measurement procedures can be merged in a single, enhanced, one. In particular, it is shown that the evaluation of the SE of enclosure in Annex H of IEC 61000-4-21, which exploits only mechanical stirring, can be improved by using the hybrid stirring, which includes also the frequency stirring thus increasing the number of uncorrelated samples. On the other hand, it is shown that at low frequencies the evaluation of the SE of enclosures based on the definition in IEEE 299.1 can be improved through the use of the maximum values of measured powers rather than the average ones. The single, enhanced, proposed procedure provides more prudent SE values than the two standards at the low frequencies, especially for standard IEEE 299.1. The presented measurement approach is supported by results obtained in three different laboratories.

On the Improvement of Shielding Effectiveness Measurements of Materials and Gaskets in Reverberation Chambers

“…The symbol || denotes the amplitude value of the parameter concerned. The number of overall samples N, which includes samples from mechanical stirring (MS) and the ones from frequency stirring (FS) when hybrid stirring (HS) is used, is assumed to be much greater than one [13]. The subscripts unc indicate that the powers or equivalently transmission coefficients are uncorrected for impedance mismatch.…”

“…The first term on the right side of (3), which is the SE of the fixture itself, is widely studied in [13]. In particular, such a ratio is considered self-correcting for impedance mismatches and clearly for antenna radiation efficiency, even though the mismatches of the two equal antennas inside the RC and fixture could be slightly different in the low frequencies.…”

“…It is important to note that the use of the maximum values is not suitable for such SE measurements as these values are not connected to the SE of the material and gasket under test. At low frequencies, the resonant behavior of the fixture produces high levels of the fields [13]. These high levels of the fields depend on the ratio between fixture sizes and working wavelengths.…”

“…For completeness of reasoning, it is specified that the use of the maximum and mean values gives the same value of SE except for the different statistical fluctuations when two equal ARCs are used and SE 4 is applied. Nevertheless, the SE achieved by maximum values has much greater statistical fluctuation [13]. However, the applicability of SE 4 implies that the chambers must meet stringent isolation conditions.…”

Experimental Investigation of the Metasurfaced Reverberation Chamber

“…The configuration details of the setup, which highlight the strategic positioning and functioning of each stirrer within the chamber, are comprehensively outlined in Ref. [10]. The meticulous arrangement of this setup played a pivotal role in maintaining stable environmental conditions throughout the experimental proceedings.…”