An efficient strategy to develop microwave shielding materials with enhanced attenuation constant

In the recent times, multifunctional materials have attracted immense interest. Self-healing polymers are in great demand in almost every coating application. With an increase in electromagnetic (EM) pollution, curbing the same has become an urgent necessity. Lightweight coatings and conducting polymeric materials are being highly researched upon in this regard, and combining these properties with self-healing systems would open new avenues in EM interference (EMI) shielding (specifically in the microwave frequency domain) applications. In the current study, a novel approach toward the development of microwave shielding materials capable of self-healing through microwave heating has been attempted. A covalently cross-linked material was developed using Diels–Alder (DA) chemistry, which shows self-healing properties when stimulated by heating. Herein, reduced graphene oxide grafted with magnetite nanoparticles (rGO/Fe 3 O 4 ) was covalently cross-linked to thermoplastic polyurethane using DA chemistry. The addition of multiwalled carbon nanotubes into these nanocomposites led to exceptional EM wave shielding and self-healing properties through a synergistic effect. The synergism led to exceptional EMI shielding of −36 dB, primarily through absorption in the microwave region of the EM spectrum. When used in the form of thin coatings of about 1 mm in thickness, the shielding value reached −28 dB, manifesting in more than 99% attenuation of EM waves through absorption. The material was also found to be capable of healing scratches or cuts through microwave irradiation.

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“…In a two-port VNA, SE is measured in terms of various scattering parameters ( S 11 , S 22 , S 12 , and S 21 ); therefore 46 …”

Section: Results and Discussionmentioning

confidence: 99%

Ultrafast Self-Healable Interfaces in Polyurethane Nanocomposites Designed Using Diels–Alder “Click” as an Efficient Microwave Absorber

2018

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“…The electrical conductivity is the most important parameter deciding about EMI shielding performance of a material . Therefore, a detailed investigation of electrical conductivity was carried out for composites and blends.…”

Section: Resultsmentioning

confidence: 99%

Graphene Derivatives Doped with Nickel Ferrite Nanoparticles as Excellent Microwave Absorbers in Soft Nanocomposites

et al. 2017

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Herein, we report the development of soft polymeric composites containing multiwall carbon nanotubes (MWNTs, 1–3 wt%) and graphene derivatives doped with nickel ferrite nanoparticles (rGO@NF, 10 wt%) as lightweight microwave absorbers. The soft nanocomposites were designed using melt‐mixed blends of varying compositions of PC (polycarbonate) and SAN (poly styrene acrylonitrile) by compartmentalized functional nanoparticles in one of the components of the blend (here PC). Maximum attenuation of the incoming electromagnetic (EM) radiation mainly through absorption was achieved. The hetero‐dielectric media at microscopic length scale in the PC component provided large interfaces which facilitated multiple scattering thereby attenuating the incoming EM radiation. This strategy of positioning the functional nanoparticles in one of the components in the blends resulted in significantly enhanced shielding effectiveness (SE), at any given concentration of MWNTs, in contrast to PC based composites. This enhancement in SE was realized in the special morphology of the bicomponent PC/SAN=60/40 wt% blends where both the components are continuous. The enhanced SE in co‐continuous blends is due to combined effect of enhanced electrical conductivity (more precisely due to interconnected network of the nanoparticles) and the presence of a hetero‐dielectric media generating large scattering interfaces. For instance, the PC/SAN (60/40 wt%) co‐continuous blend containing 3 wt% MWNTs and 10 wt% rGO@NF manifested in a total shielding effectiveness (SET) of −32.3 dB (i. e. more than 99.9 % attenuation of incoming EM radiation) mainly through absorption.

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“…However, it is believed that when the shield thickness exceeds the skin depth of the shield, the contributions from multiple reflections is neglected since whatever wave is reflected from the inner surface of the shield will eventually get absorbed by various conducting particles in the shield. In a vector network analyser (VNA), SE is measured,

true {S E}_{T} = 10 l o g {(||, \frac{1}{S_{12}})}^{2}

true {S E}_{R} = 10 l o g (||, \frac{1}{(() 1 - S_{11}^{2})})

true {S E}_{A} = 10 l o g (||, \frac{1 - S_{11}^{2}}{S_{12}^{2}})

…”

Section: Effect Of Alloy/ Mwnt Heterostructure Particles On Electromamentioning

confidence: 99%

Magnetic Alloy‐MWNT Heterostructure as Efficient Electromagnetic Wave Suppressors in Soft Nanocomposites

2017

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FeNi (iron‐nickel) alloy particles were coated with MWNTs (Multiwalled carbon nanotubes) using simple ball milling technique at various alloy to MWNT ratios. These hybrid heterostructure were then dispersed in PVDF/TPU (Polyvinylidene fluoride/ Thermoplastic polyurethane) blends to develop flexible composite materials that can shield electromagnetic (EM) radiations. These alloy particles coated with MWNT localise mostly in the TPU phase of the binary blends. The shielding effectiveness (SE) measurements obtained from the scattering parameters reveal that for a particular ratio of FeNi/MWNT (3:1), the SE was the highest (‐35.7 dB) among the different composites studied here and manifested in improved microwave absorption in the blends. The absorption driven shielding is due to various polarization in the shield, thereby increasing the dielectric loss. It was observed that these MWNT wrapped magnetic alloy particles shielded the incoming EM radiations more effectively as compared to only MWNTs or only alloy particles. The soft nanocomposites designed here absorb up to 95 % of the incoming EM radiations. The lowest skin depth and highest specific EMI (Electromagnetic interference) shielding attained was 1.4 mm and −20.5 dB cm2 g−1 respectively for composites containing FeNi/MWNT‐ 3:1. The attenuation constant derived from different parameters of these blends were also analysed in order to develop a multi‐layered structure, having absorption‐multiple reflection‐absorption pathways. This was used to assess the effect of different layers and their sequence in the multi‐layered structure on final EM wave attenuation. Interestingly, multi‐layered architecture with a similar thickness showed three‐fold increase in the total shielding as compared to their bulk counterpart.

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An efficient strategy to develop microwave shielding materials with enhanced attenuation constant

Cited by 23 publications

References 52 publications

Ultrafast Self-Healable Interfaces in Polyurethane Nanocomposites Designed Using Diels–Alder “Click” as an Efficient Microwave Absorber

Ultrafast Self-Healable Interfaces in Polyurethane Nanocomposites Designed Using Diels–Alder “Click” as an Efficient Microwave Absorber

Graphene Derivatives Doped with Nickel Ferrite Nanoparticles as Excellent Microwave Absorbers in Soft Nanocomposites

Magnetic Alloy‐MWNT Heterostructure as Efficient Electromagnetic Wave Suppressors in Soft Nanocomposites

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