Investigation on some shielding solutions to electromagnetic interference problems

Abstract

Shielding is a classical method to control the Electromagnetic Interference EMI It is used in myriad of interference scenario At the equipment level it is used in the form of metallic enclosure to reduce electromagnetic radiation from high speed digital electronics housed inside It is also used in the form of Frequency Selective Surface FSS to address the security and interference related concerns in today s wireless networks Frequency selective surface FSS wall with band stop characteristics is used for this purpose newlineIn typical equipment with shielding enclosure EMI above 200 MHz is dominated by the radiation from the apertures and the slot Radiation from the internal electronics coupled to apertures and slots through enclosure cavity resonance can result in significant radiation from the enclosure Enhanced radiation due to cavity resonance may render equipment non compliant to various CISPR and FCC standards In this thesis work a new approach of selective use of absorbing material is proposed to improve the enclosure shielding effectiveness at the cavity resonances It is shown that by deploying the magnetic absorber strips partially inside the enclosure significant reduction in the EMI due to cavity resonance can be obtained Numerical method is used to identify the optimum location of the absorber strip in the enclosure It was found that by deploying absorber strips along the four edges of the enclosure floor reduction of 10 12 dB in radiated EMI at cavity resonances can be obtained newline newline