Electromagnetic Shielding Materials in GHz Range

Abstract

The state-of-the art in the design and the manufacture methods of the different electromagnetic shielding materials has been reviewed. This topic has become a mainstream field of research because of the electromagnetic pollution generated by telecommunication technology development. The review is centred in absorbent materials and shows a general overview of how the absorption properties of such composites can be tailored through changes in geometry, composition, morphology, and the filler particles content. Although different types of materials are explained, the text is mainly focused on carbon materials such as graphene and carbon nanotubes. In this way, the importance of the dispersion of the conductive fillers in different polymer matrices is discussed. In addition, an extensive study on new complex architectures such as foam-based materials is presented. Finally, the combination of carbon fillers with other constituents such as metallic nanoparticles is mentioned. In all these studies, the efficiency of the composites as absorbent or reflective of electromagnetic radiation is discussed.

Unprecedented Electromagnetic Interference Shielding from Three-Dimensional Bi-continuous Nanoporous Graphene

“…One of the feasible strategies for coping with the conflicting demands of a lightweight and thin material with immense EMI SE is to explore high connectivity and electrical conductivity of 2D graphene in a 3D bi-continuous nanoporous configuration with a smaller nanopore size and a large internal surface area as blocking interfaces of EMI SE. 33 With this in mind, utilizing nanoporous metal-based CVD growth of bi-continuous nanoporous graphene for the first time, we have succeeded in overcoming the complications by integrating lightweight, thinness, mechanical flexibility, high electrical conductivity, and excellent SE into one environmentally stable carbon-based material. The resultant graphene films with a bi-continuous nanoporosity exhibits an outstanding EMI SE (SSE/t) of 50.9 dB (75,407 dB cm 2 g À1 ) and 83 dB (61,630 dB cm 2 g À1 ) at thicknesses of 150 and 300 mm, respectively, the best EMI-shielding performances among all 3D carbon materials known to date.…”

“…1,25 It is well known that the EMI SE of porous materials does not solely originate from the intrinsic electrical conductivity but also from the contribution of the internal surfaces, which has not been considered in the theoretical model. 25,33 In this regard, porous materials effectively minimize the impedance mismatch between incoming and propagating media and allow a large portion of the incident EMWs to penetrate and interact within pore channels and their conductive walls, rather than reflecting them passively from the outer surfaces, which is the dominant mechanism in dense conductive materials. 8,26,33 In principle, the highly conductive porous networks of nanoporous graphene provide abundant conductive interfaces that multiply internal reflections and greatly attenuate the incident EM waves inside the material by converting the induced currents into heat, dielectric relaxation, and tunneling currents, thus enhancing the electromagnetic wave absorption.…”

“…25,33 In this regard, porous materials effectively minimize the impedance mismatch between incoming and propagating media and allow a large portion of the incident EMWs to penetrate and interact within pore channels and their conductive walls, rather than reflecting them passively from the outer surfaces, which is the dominant mechanism in dense conductive materials. 8,26,33 In principle, the highly conductive porous networks of nanoporous graphene provide abundant conductive interfaces that multiply internal reflections and greatly attenuate the incident EM waves inside the material by converting the induced currents into heat, dielectric relaxation, and tunneling currents, thus enhancing the electromagnetic wave absorption. 11,33 Therefore, when the thickness increases, the incoming EMWs are absorbed by means of enhanced multireflections for superior EMI SE by interacting with more conductive graphene walls than the thinner nanoporous samples.…”

“…8,26,33 In principle, the highly conductive porous networks of nanoporous graphene provide abundant conductive interfaces that multiply internal reflections and greatly attenuate the incident EM waves inside the material by converting the induced currents into heat, dielectric relaxation, and tunneling currents, thus enhancing the electromagnetic wave absorption. 11,33 Therefore, when the thickness increases, the incoming EMWs are absorbed by means of enhanced multireflections for superior EMI SE by interacting with more conductive graphene walls than the thinner nanoporous samples.…”

“…Electrical conductivity (s) is the primary factor determining reflection, absorption, and the overall shielding efficiency according to the equation EMI SE = ½8:7dðpf msÞ 0:5 , where the first and second terms are related to reflection and absorption, respectively; and f and m are frequency and permeability, respectively. 18,33 Additionally, taking advantage of the contribution from the internal multiple reflections, the lightweight nanoporous structure provides lower overall densities and adequate shielding compared with their solid counterparts at minimal thickness. Therefore, the term specific electromagnetic interference shielding effectiveness (SSE/t) appropriately accounts for the influences of both weight and thinness in one material and is a more realistic criterion when designing and evaluating shielding behavior for applications in aerospace, aviation, energy storage and conversion, and flexible touch screens.…”