Functional Magnetic Nanocomposites for EMI Shielding

Electromagnetic interference (EMI) shielding is a process of limiting the flow of electromagnetic fields between two locations by reflection and/or absorption of electromagnetic wave by use of a shielding material against the penetration of incoming radiation. Due to the strong requirement of today's society for dependable electronic devices, and the rapid growth of radio frequency radiation sources, enhanced materials with better EMI shielding characteristics against electronics and radiation sources are increasingly needed. A combination of magnetic and conductive materials can be used to improve the capability of EMI shielding materials at a much broader frequency range. Here, magnetic nanocomposites were prepared by an in-situ oxidative polymerization method to encapsulate different loadings of iron oxide nanoparticles (MNP) by a conductive polymer, polypyrrole (PPy). The morphology, DC conductivity, magnetic and electromagnetic interference (EMI) shielding behaviors of the nanocomposites dispersed in epoxy resin were characterized, the latter by use of a vector network analyzer in a frequency range of 0.1-18 GHz. Nanocomposites of MNP/PPy showed a marked increase in the absorption of 10.10 dB at the maximum frequency limit (17-18 GHz) of the instrument, in comparison to the absorption bands for PPy particles only (7.5 dB), MNP only (2.6 dB), or physical blends of MNP and PPy particles (3.6 dB) in the resin. The mechanism of this enhancement is discussed based on electromagnetic theory. The marked improvement on the absorption of electromagnetic waves can be partly attributed to good dispersion of the PPy-encapsulated magnetic nanoparticles in the matrix, but more importantly to the direct connectivity between the magnetic and the conductive phases. The study demonstrates the possibility of improving shielding performance by utilising composite magnetic and conductive nanocomponents. Other processing methods including microwave plasma treatment to improve the crystallinity of different nanocomposites and possible phase change conducive to better shielding properties (e.g. amorphous to graphitic carbon for better conductivity, maghemite to magnetite to increase magnetisation) will be discussed.