Suppression of radiated electromagnetic emissions using absorbing frequency selective surfaces

In this paper, a Frequency Selective Surface (FSS) is designed to act as an absorber of electromagnetic emissions at 8GHz. The designed FSS covers the top inside wall of the case box of a digital system and reduces the leaked radiations through the airflow slots. Resistive thin layers are used to create a low profile FSS with a 2-D array of square patches in two layers. An equivalent circuit is presented to provide closed-from relations for designing the FSS layout at the desired frequency. It is shown that the surface input impedance of FSS is matched to the intrinsic impedance of a plane wave in free space. Absorption versus incidence angle of incoming plane waves is evaluated through full-wave simulations showing a maximum value of 32dB. Simulations of radiated emissions from the enclosure box with and without absorbing FSS demonstrate 9dB improvement when the custom-designed FSS is used.