Porous Carbon Materials and Their Composites for Electromagnetic Interference (EMI) Shielding: The State-of-the-Art of Technologies

Abstract

Portable gadgets and electronic devices are pervasive in any modern society today. However, these devices transmit electromagnetic radiations in radio frequency range called electromagnetic interference (EMI) which interfere with other electronic technologies. One of the most common hazards of EMI is the harm it can cause to medical devices and make them unreliable. Apart from this, EMI may affect the human tissue as well as can ignite flammables if not shielded. Hence, it is necessary to develop a material to absorb these EM waves. EMI shielding blocks radio frequency (RF) electromagnetic radiation and can reduce the coupling of radio waves, electromagnetic fields, and electrostatic fields. EMI shielding depends mainly on electrical conductivity and magnetic permeability of shield material, the frequency of radiation. EMI shielding mainly involves three mechanisms: reflection, absorption, and multiple reflection. Reflection is often known as the primary mechanism for EMI where the shield material should possess mobile charge carriers such as electrons or holes, which interact with the EM field in the radiation. Since metals have more free electrons, they attenuate EM radiation significantly by reflection. For shielding by absorption, the shield should possess either electrical or magnetic dipoles, which interact with incoming EM radiation and help in the attenuation of EM radiation by absorption. Materials having a high dielectric constant, such as zinc oxide or barium titanate, may provide electric dipoles, while materials having a high magnetic permeability, such as ferrite or nickel, may offer magnetic dipoles. Multiple reflections also help in the attenuation of EM radiation. There are variety of materials employed for the fabrication of EMI shielding application including metals, polymers, carbon, ceramics, and their composite materials. Among these materials, the demand of carbon materials and their composites is growing for EMI shielding. Carbon materials are more attractive over metals which are by far the most common materials for this application, due to their oxidation resistance, chemical and thermal stability as well as lower density, and high dielectric loss properties. Since last two decades, among other 1D and 2D carbon-based materials; 3D porous graphite and amorphous carbon have been successfully developed, and their microwave absorption performance has been tested by many researchers. This chapter summarizes the state-of-the-art technological advanced in the area of EMI shielding with the focus on carbon and carbon-based composites.