With the rapid arising of information technology, microwave absorbing materials (MAMs) are playing an increasingly significant role in electronic reliability, healthcare, and national defense security. Hence, development of high performance MAMs with thin thickness, low density, wide bandwidth, and strong absorption has attracted great interests. Recently, taking graphene as MAMs for high-performance electromagnetic (EM) wave attenuation has grabbed considerable attention, owing to their low density, high specific surface area, strong dielectric loss, and high electronic conductivity. Furthermore, in order to address the interfacial impedance mismatching of the sole graphene materials, incorporation of other lossy materials has been widely studied as the imperative solution to improve its MA performance. In this review, we introduce the theory of microwave absorption and summarize recent advances in the fabrication of graphene-based MAMs, including rational design of the microstructure of pure graphene and tunable chemical integrations with polymers, magnetic metals, ferrites, ceramics, and multicomponents composites. The key point of enhancing MA in graphene-based MAMs is to regulate their EM properties, improve of impedance matching, and create diversified loss mechanisms. Furthermore, the shortcomings, challenges, and prospects of graphene-based MAMs are also put forward, which will be helpful to people working in the related fields.

Graphene-based microwave absorbing composites: A review and prospective

The rapid proliferation and elevated usage of electronic devices have led to a meteoritic rise in electronic pollutions such as electronic noise, electromagnetic interference (EMI) and radiofrequency interference (RFI) which leads to improper functioning of electronic devices. Metals and their alloys can serve as the best EMI shielding materials but their heavy weight, high cost and low corrosion resistance have limited their applications in EMI shielding. The emergence of flexible polymer composites have substituted the metal and metal alloy based EMI shielding materials due to their unique features such as light weight, excellent corrosion resistance, superior electrical, dielectric, thermal, mechanical and magnetic properties that are highly useful for suppressing the electromagnetic noises. In this review article, the EMI shielding effectiveness of flexible polymer composites comprising of metals and various forms of carbon nanofillers such as carbon black, carbon nanofibers, carbon nanotubes, graphite, graphene, graphene oxide, graphene nanosheets, graphene nanoribbons and graphene nanoplatelets have been deeply reviewed.

Recent advances in electromagnetic interference shielding properties of metal and carbon filler reinforced flexible polymer composites: A review

Recent advances in carbon-based polymer nanocomposites 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.

A review of porous lightweight composite materials for electromagnetic interference shielding

Carbon materials and their composites for electromagnetic interference shielding effectiveness in X-band

The advent of graphene heralded by the recent studies on carbon based conducting polymer composites has been a motivation for the use of graphene as an electromagnetic interference (EMI) shielding material. One of the variants of graphene, graphene nanoribbon (GNR) shows remarkably different properties from graphene. The EMI shielding effectiveness of the composite material mainly depends on fillers’ intrinsic conductivity, dielectric constant and aspect ratio. We have synthesized graphene nanoribbon (GNR) – Polyaniline (PANI) – epoxy composite film for effective shielding material in the X-band frequency range of 8.2–12.4 (GHz). We have performed detailed studies of the EMI shielding effect and the performance of the composite and found that the composite shows ∼−40 dB shielding which is sufficient to shield more than 95% of the EM waves in X Band. We checked the shielding effectiveness of the composite film by varying the GNR percentage and the thickness of the film. The strength properties of the synthesized composited were also studied with a aim to have a material having both high strength and EMI shielding properties.

Processing of graphene nanoribbon based hybrid composite for electromagnetic shielding

A very thin graphene nanoribbon/polyvinyl alcohol (GNR/PVA) composite film has been developed which is light weight and requires a very low concentration of filler to achieve electromagnetic interference (EMI) shielding as high as 60?dB in the X band. Atomic force microscope studies show very well conjugated filler concentration in the PVA matrix for varying concentrations of GNR supported by Raman spectroscopy data. The films show 14 orders of increase in conductivity with a GNR concentration of 0.0075?wt% in PVA. This is possible because of the interconnected GNR network providing a very low percolation threshold as observed from the electrical measurements. Local density of states study of GNR using scanning tunnelling spectroscopy shows the presence of localized states near the Fermi energy. There are multiple advantages of GNR as an EMI shielding material in a polymer matrix. It has good dispersion in water, the conductive network in the composite shows very high electrical conductivity for a very low concentration of GNR and the presence of localized density of states near Fermi energy provides the spin states required for the absorbance of radiation energy in the X band.

https://iopscience.iop.org/article/10.1088/0957-4484/24/45/455705/pdf

Graphene nanoribbon–PVA composite as EMI shielding material in the X band

There was an error in calculating the weight percentage of the graphene nanoribbon (GNR) in PVA. There were three films made with different concentrations of GNR. The correct weight percentage of GNR in PVA in three films should be 0.75%, 1.5% and 2.5% instead of 0.0075 wt%, 0.015 wt%, and 0.025 wt% respectively. Reference to the weight percentage has been made in the abstract, line 5; page 3, paragraph 5, second line; page 4, paragraph 1; page 6, paragraph 2, line 6; figure caption 4; figure caption 10 and figures 9 and 10, the corrected versions of which are shown below.

Corrigendum: Graphene nanoribbon–PVA composite as EMI shielding material in the X band (2013 Nanotechnology 24 455705)

One hundred twenty five cases of lepromatous leprosy and 25 cases of tuberculoid leprosy were investigated for audiovestibular status. Impaired hearing was detected in 52 percent and vestibular hypofuction in 7.2 per cent of lepromatous cases. Conductive deafness was due to eustachian tube catarrh secondary to atrophic rhinitis associated with the disease. The perceptive deafness and vestibular hypofuction were due to end organ lesion probably due to E.N.L. reaction. The vestibulococlear nerve involvement was considered to be unlikely. In tuberculoid leprosy derangement in hearing was not observed in any cases.

Evaluation of audiovestibular status in leprosy.

Audio-vestibular evaluation was carried out in 50 leprosy patients consisting of 30 lepromatous and 20 tuberculoid cases No abnormality was observed in the tuberculoid patients Impaired hearing was detected in half of the lepromatous patients and vestibular hypofunction was observed in a small number of cases The Conductive deafness was due to eustachian tube catarrh and otitis media, secondary to lepromatous involvement of the nose The Sensori-neural deafness and vestibular hypofunction were possibly due to an end organ lesion and involvement of the vestibulocochlear nerve was considered to be unlikely

Rajvinder Singh

Papers

Processing of graphene nanoribbon based hybrid composite for electromagnetic shielding

Graphene nanoribbon–PVA composite as EMI shielding material in the X band

Corrigendum: Graphene nanoribbon–PVA composite as EMI shielding material in the X band (2013 Nanotechnology 24 455705)

Evaluation of audiovestibular status in leprosy.

Audio-vestibular study in leprosy