Experimental investigation of degradation and non-linear effects in corroded EMC joints exposed to high power microwaves (HPM)
Publish date: 2004-01-01
Report number: FOI-R--1246--SE
Written in: English
Determination of shielding effectiveness is a vital part in the analysis of a systems capability to withstand HPM. It is usually assumed that the shielding effectiveness, determined at low field levels, is valid at HPM threat levels. This assumption might be refuted by the presence of non-linear effects, e.g. due to electrical discharge or metal insulator-metal junctions caused by corrosion (the "rusty bolt effect"). Non-linear effects may result in damage of the shielding joint and/or in generation of new frequency components in the spectrum of the transmitted pulse. Measurements have been performed on 31 corroded EMC joints. No major degradation could be detected after HPM irradiation at 3 GHz. Also, most of the objects showed only limited changes of the time domain shape of the transmitted pulse. Most of the objects showed none, or only a moderate generation, of harmonics. However, many of these latter objects indicate a significant spectral content below and around 1 MHz. A preliminary analysis, made difficult by present measurement set-up, indicates that the energy content of the transmitted pulse at low frequencies in some cases might be of the same order as that around 3 GHz. This will be further investigated in the future.