Mechanistic Insights for Controlling Electromagnetic Interference Shielding Through Microwave Absorption in Magnetic Composites

Abstract

Extensive use of electronic devices in daily communication and information technology causes high (microwave) frequency electromagnetic interference (EMI). This EMI often leads to noise, data misinterpretation or malfunctioning of electronic devices such as medical equipment. To protect the device from this unwanted EMI, a shield layer is essential, which can shield the device from the unwanted radiation via either reflection or absorption. As the reflected microwave may cause further EMI, the later phenomenon is advantageous, because it forbids any further interference with neighboring devices. This absorption-based shielding is also useful in stealth technology to design radar camouflage military aircraft. Metallic shields normally reflect the microwave and are heavy. To address this issue one requires shield layers with lightweight and conducting. In this respect, conducting polymer-based or metallic nanoparticles based composites seems handy. Hence, in this thesis work, we have adopted various strategies to design composites that can address the above limitations of metallic shields. We have demonstrated that the scattering, reflection and absorption of microwave depend upon the micro and macroscopic properties of the filler particles. Such properties include concentration, size, morphology, conductivity, defects and magnetism of the filler materials. We have systematically investigated their effect on EMI shielding to validate our strategies. We used composites of conducting polymer (Polyaniline), hard ferrimagnetic hexaferrites, soft magnetic Yttrium Iron Garnet (YIG), metallic iron particles, metal (Fe/Co/Ni) doped carbonaceous materials along with microwave transparent paraffin wax or PVDF. The effect of concentration, size, morphology, conductivity, defects and magnetic properties of these fillers in these composites on EMI shielding is studied. Furthermore, to understand the atomistic mechanism of shielding through light-matter interactions, complex permittivity and permeability of composites used...