Damping resonances of a screened enclosure using absorbing material

In this paper an analysis of a method to damp resonances inside a screened room is done. The room shall be part of a big system, e.g. a ship. This implies that it cannot be shielded electromagnetically to a high degree as it must contain connections to its exterior like cables, venting slots and doors. If the system is exposed to high field strengths, caused e.g. by an electromagnetic pulse (EMP) or intentional electromagnetic interference (IEMI), resonances are excited in that room. At the resonance frequencies, the room acts as an antenna and the shielding mechanisms collapse. It may contain electromagnetically sensitive devices, that have to be protected against electromagnetic interference (EMI). A possibility to suppress the resonances is inserting absorber material into the room. In this paper a screened enclosure with an aperture is analyzed with and without absorber lining on the wall opposite to the aperture in order to obtain the damping of the resonances in the cavity. Measurement and simulation of the damping are done in order to verify each other. For the simulation the permittivity of the absorber material has to be known. It is measured by the transmission/reflection method using the Nicolson-Ross-Weir algorithm. The results show that resonances in screened rooms can be damped in this way by up to 30 dB.