High frequency millimetre wave absorbers derived from polymeric nanocomposites

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A comprehensive review on mechanical, electromagnetic radiation shielding, and thermal conductivity of fibers/inorganic fillers reinforced hybrid polymer composites

Homogenously dispersed nanoparticles having a magnetic core and graphitic-carbon shells in amorphous carbon globules are prepared using a low-cost pyrolysis technique. Synergetic microwave absorption in carbon globules embedded with nanoscale iron/iron-carbide graphite (FeC) particles via dielectric, magnetic and Ohmic losses is emphasized in this work. The electromagnetic interference (EMI) shielding properties of the FeC nanoparticles dispersed in polyvinylidene fluoride (PVDF) are studied in the 8–18 GHz frequency range and compared with those of PVDF composites containing similar weight fractions of conducting/magnetic phase micro-particles such as carbonyl iron (CI) or electrolytic iron (EI) or a similar amount of amorphous carbon phase such as amorphous carbon (a-C) globules. The PVDF/FeC composite shows a maximum SET value of −23.9 dB at 18 GHz, as compared to the SET for the other composites. The enhanced EMI shielding in the PVDF/FeC composite is attributed to the increased interfaces of the nanoscale particles, which facilitate enhanced Maxwell–Wagner interfacial polarization. The homogenous dispersion of iron and iron-carbide phases in the carbon matrix of the FeC sample enhances the interfacial polarization and multiple internal scattering of the penetrated EM waves, which get synergistically attenuated by the Ohmic, magnetic and dielectric losses. Based on complex permittivity and permeability results we have calculated the Reflection Loss (RL) of the PVDF/FeC composite. The PVDF–FeC composite shows a RL peak of −40.5 dB for a 4.3 mm thick specimen positioned at 5 GHz frequency. The RL peak is explained using the quarter-wave cancellation model. Our work demonstrates that incorporating carbon globules containing nanoscale magnetic and conducting particles in a polymer matrix, provides an effective way to enhance EMI shielding via absorption of the EM wave in a lightweight thin composite coating.

Carbon encapsulated nanoscale iron/iron-carbide/graphite particles for EMI shielding and microwave absorption

The microwave absorption properties of silicone rubber containing various graphene products acquired from different sources were studied. The complex permittivity, permeability, and return loss (RL) of the composites in the range of 3–18 GHz were characterized using contactless free-space measurement geometry. The large differences in the permittivity and RL for all samples indicated that the quality of graphene significantly affected the microwave absorption of the composite. Among the graphene samples, our homemade Staudenmaier reduced graphene oxide (RGO) offered a significantly improved RL at very low loading of 1 wt%, its minimum RL reached −37.8 dB at 12.3 GHz with a thickness of 2.5 mm. To identify the key factor that caused the difference in the microwave characteristics, the material properties of the graphene samples, including surface morphology, specific surface area, and C/O ratio, were analyzed and compared. The comparison revealed that the specific surface area, which is an indicator of the degree of exfoliation, is the most critical property that affects the microwave absorption performance of graphene-filled composites. Our results indicated that a well-dispersed, highly exfoliated RGO is capable of providing excellent microwave absorption at very low loading, which is favorable for cost reduction in future applications.

Remarkable microwave absorption performance of graphene at a very low loading ratio

The explosive progress of electronic devices and communication systems results in the production of undesirable electromagnetic pollution, known as electromagnetic interference. The accumulation of electromagnetic radiation in space results in the malfunction of commercial and military electronic appliances, and it may have a negative impact on human health. Thus, the shielding of undesirable electromagnetic interference has become a serious concern of the modern society, and has been a very perspective field of research and development. This paper provides detailed insight into current trends in the advancement of various polymer-based materials with the effects of electromagnetic interference shielding. First, the theoretical aspects of shielding are outlined. Then, the comprehensive description of the structure, morphology and functionalization of the intrinsic conductive polymers, polymers filled with the different types of inorganic and organic fillers, as well as multifunctional polymer architectures are provided with respect to their conductive, dielectric, magnetic and shielding characteristics.

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Roopas Kiran Sirugudu

Papers

Effect of silver incorporation into PVDF-barium titanate composites for EMI shielding applications