A review of porous lightweight composite materials for electromagnetic interference shielding

Lightweight porous materials for electromagnetic interference (EMI) shielding applications are reviewed. EMI shielding refers to the capability of a material to protect from electromagnetic fields (EMFs) generated by electronic devices. Traditionally conducting metals are used in EMI shielding applications, which are slowly being replaced by conducting polymer based shields. This review is narrowly focused on understanding the approaches related to porous high EMI shielding composite materials that have very low density values. While metallic fillers can increase the EMI shielding capabilities of polymers, they also increase the weight, which can be offset by inducing the porosity in the matrix. Porosity is found to be effective in providing higher shielding effectiveness at low filler volume fraction due to concentrating the filler in the solid polymers. However, use of gas porosity results in composites with low mechanical properties. This problem can be alleviated to some extent by reinforcing polymer foams with lightweight conductivefillers such as carbon nanofibers (CNFs), carbon nanotubes (CNTs) and graphene. But the properties of pores such aspore size and distribution cannot be effectively controlled in such cases. Syntactic foams containing hollow particle fillers seem to be the best combination of EMI shielding capabilities and mechanical properties. These composites can be either filled with a second phase conducting filler, or hollow particles can be coated with a conducting layer, or hollow particles made of conducting materials can be used as fillers. The hollow particle wall thickness and volume fractions can be optimized to obtain the desired combination of properties in syntactic foams to enable their multifunctional applications.