Shielding effectiveness of mechanical feed through elements used in a GTEM cell

Often shielding cabins are equipped with mechanical set ups that require feed throughs such as ball bearings. Hence a metal axis enters the cell. Due to the imperfect conductivity of the ball bearing an outer field can enter the inside of the enclosure. In order to investigate the shielding effectiveness of ball bearings, special set ups are constructed to analyze different ball bearings under different conditions. Investigations are mostly done in the frequency domain. Nevertheless, to give an example, a ball bearing has been stressed by a UWB pulse that has been injected in a coaxial cable. The results are presented in the time domain. Further the different ball bearing types have been modeled using simple networks of lumped elements that are able to simulate the frequency behavior of the bearings.