Studies on composite media as electromagnetic interference (EMI) shielding materials

This thesis addresses pertinent studies concerning the use of electromagnetic composite media as EMI shielding materials. Specifically biphasic composites constituted by conducting and/or lossy inclusions dispersed in a dielectric host are considered. The effects of conductivity and/or dielectric loss, shape, size and volume fraction of the included component in deciding the shielding effectiveness of the composite material are ascertained over radio frequency spectrum. Theoretical studies in modeling the effective complex permittivity of the test composite are presented in the classical and state-of-the-art perspectives and hence the shielding effectiveness of the test composite is elucidated. The theoretical considerations also refer to two types of inclusions namely, conducting particulates (metallic particles, fibers and flakes), and lossy nonmetallic inclusions. In the first case the host-inclusions system refers to polemically opposite constituents and in the later case, it is simply a dielectric-dielectric mixture. Experimental studies to evaluate the shielding effectiveness of a set of test composite are presented. Relevant descriptions include details on the test composites synthesized, experimental arrangement and the test procedure followed. Particulars on test materials constituted by a host ceramic medium (such as TiO2) with conducting inclusions such as iron particles, copper rods and aluminum flakes are presented. Measured results on the shielding effectiveness of these materials over the frequency range (200 to 1500 MHz) are listed and compared with theoretical results. Conclusions and discussions as regard to pertinent applications of such materials are presented.