Electromagnetic Shielding Applications Research Articles

Scalable, Highly Conductive, and Micropatternable MXene Films for Enhanced Electromagnetic Interference Shielding

Summary Two-dimensional transition metal carbides and nitrides (MXenes) have accumulated tremendous interest recently due to their high conductivity and excellent figures of merit in electromagnetic interference shielding and other applications. Large-area freestanding films of MXenes are important for versatility in application; however, alternative processing methods are needed for large-scale production. In this work, we demonstrate fabrication of Ti3C2Tx MXene freestanding films through drop-casting onto hydrophobic plastic substrates. Freestanding MXene films prepared using the drop-casting method can be fabricated in large areas (>125 cm2) and thicknesses (23.2 μm), and have smooth surfaces (14 nm RMS roughness) while maintaining high electrical conductivity (~7,000 S cm−1). Moreover, these MXene films can be micropatterned in three dimensions by processing on commercially available microstructured plastics, resulting in a 38% increase in normalized electromagnetic interference shielding efficiency compared with flat films. The results presented here suggest a scalable path toward creating MXene freestanding films for prototypes and industrialization.

Graphene and MnO2 decorated graphene filled composites for electromagnetic shielding applications having excellent dielectric properties

Graphene nanoplatelets (GnP) and α-MnO2 decorated GnP were integrated into an ethylene vinyl acetate (EVA) matrix using the dual mixing method (solution followed by melt mixing). GnP was added in 1, 3, 5, 8, 10 and 15 phr loadings into an EVA matrix to obtain composites and evaluate their various properties suitable for mechanical and electrical applications. The graphene nanoplatelets were further decorated with α-MnO2 which was subsequently integrated into EVA at an 8 phr loading to form composites. It was observed in the GnP-EVA composites, that with an increasing GnP content, a substantial increase in the tensile strength (188%) over the neat polymer was observed at a 10 phr loading but reduced thereafter at a 15 phr loading. Dielectric permittivity of the composites were observed to increase with an increasing filler loading, the addition of α-MnO2 also having a beneficial effect. Conductivity as well as the electromagnetic interference shielding performance were improved with increasing GnP concentrations. A maximum 28 dB of shielding was observed in the 15 phr loaded GnP-EVA composite whereas the α-MnO2 decorated GnP-EVA composite showed a shielding efficiency of 22 dB at a concentration of 8 phr for a thickness of 2 mm with excellent thermal and mechanical properties. Overall, the composite material will find its application as a flexible EMI shielding material.

Near-Field Shielding Analysis of Single-Sided Flexible Metasurface Stopband TE: Comparative Approach

Near-field (NF) studies comprising four common 10 GHz stopband frequency selective surfaces (FSSs) of single-sided, single-layer metasurfaces are conducted. The studies are to determine the NF efficiency of the metasurfaces for electromagnetic shielding applications. First, the FSSs' shielding performance in both far-field (FF) and NF zones is considered using the finite element method (FEM) based on the cell shielding effectiveness (SE). Analytical derivations of the FF- and NF-SE are presented, incorporating the equivalent circuit model and infinitesimal electric/magnetic source model, respectively. A nonlinear regression learning approach is utilized to predict an acceptable NF model. In the comparison study, the edge diffraction effects due to the finite structures are taken into consideration for 1-D and 2-D diffractions. The NF-SE performance of conformal structures is analyzed based on the radii of curvature. When the structure is bent, the movement of the desired transmission zero in the NF region intensely degrades the NF-SE, which may lead to a highly unstable shielding performance. Moreover, data sets are extracted for efficient usage of the structures under test by introducing two useful reconfigurable parameters, distance and radius. For verification, the FEM results are compared with the method of moment (MOM) results. The developed scenarios create a reliable criterion for further advancements of the flexible shielding surfaces from the NF point of view.

Well-posedness theory for electromagnetic obstacle problems

This paper develops a well-posedness theory for hyperbolic Maxwell obstacle problems generalizing the result by Duvaut and Lions (1976) [5]. Building on the recently developed result by Yousept (2020) [30], we prove an existence result and study the uniqueness through a local H(curl)-regularity analysis with respect to the constraint set. More precisely, every solution is shown to locally satisfy the Maxwell-Ampère equation (resp. Faraday equation) in the region where no obstacle is applied to the electric field (resp. magnetic field). By this property, along with a structural assumption on the feasible set, we are able to localize the obstacle problem to the underlying constraint regions. In particular, the resulting localized problem does not employ the electric test function (resp. magnetic test function) in the area where the L2-regularity of the rotation of the electric field (resp. magnetic field) is not a priori guaranteed. This localization strategy is the main ingredient for our uniqueness proof. After establishing the well-posedness, we consider the case where the electric permittivity is negligibly small in the electric constraint region and investigate the corresponding eddy current obstacle problem. Invoking the localization strategy, we derive an existence result under an L2-boundedness assumption for the electric constraint region along with a compatibility assumption on the initial data. The developed theoretical results find applications in electromagnetic shielding.

Scalable fabrication of highly crosslinked conductive nanofibrous films and their applications in energy storage and electromagnetic interference shielding

With their unique properties and potentials in several critical applications, highly crosslinked and conductive nanofibrous films (HCC-NFs) have attracted broad attentions recently. However, it is still a great challenge to produce high-performance and uniform HCC-NFs with controllable thickness on a large-scale. Electrospinning could be used to fabricate nanofiber films, but it falls short in creating intimate mechanical and electrical joints between adjacent nanofibers for crosslink. Herein, a new strategy inspired by the fabric shrinking when drying was applied to produce HCC-NFs. Hydrophilically-engineered electrospun polyacrylonitrile (PAN) nanofiber film was dip-coated in a water solution of PEDOT:PSS, and was then dried naturally. By preventing contraction of the film in its lateral plane while allowing its thickness shrinking, the capillary effect during water evaporation resulted in collapse of the large pore volume in the film and the subsequent joint formations between PEDOT:PSS-coated PAN nanofibers, which are further cemented together by the conductive polymer coating. The electrochemical, electrical and mechanical properties of such fabricated HCC-NFs were studied, and they were successfully applied as electrodes to demonstrate high-rate supercapacitors and as a flexible porous material for electromagnetic interference (EMI) shielding. The studies suggest HCC-NFs produced by this facile method have promising prospects in several applications.

Polypyrrole and cellulose nanofiber based composite films with improved physical and electrical properties for electromagnetic shielding applications

Polypyrrole (PPy) and cellulose nanofiber (CNF) based conducting composite films were synthesized using two new approaches, in-situ polymerization of pyrrole onto cellulose nanopaper (PPy/CNP) and polyvinyl alcohol coated cellulose nanopaper (PPy/PVA-CNP). Significant improvement in the conductivity, tensile strength, water resistance, and electromagnetic shielding effectiveness (SE) was observed for these composite films compared to commonly used in-situ nanofiber (ISF) approach, where PPy is coated on nanofibers prior to film preparation. Maximum improvement in conductivity, SE and tensile strength of PPy/PVA-CNP compared to ISF films was attributed to highly uniform and compact PPy coating and reduced porosity. SE of -23 dB (thickness upto 138.4 μm) and tensile strength of 103.8 MPa for PPy/PVA-CNP films are the highest values found in the literature for PPy and CNF based composite films at a comparable thickness. These new approaches could enable a scalable preparation of flexible conducting composite films with superior physical and electrical properties for EMI shielding applications.

Emerging trends in poly(methyl methacrylate) containing carbonaceous reinforcements—Carbon nanotube, carbon black, and carbon fiber

Poly(methyl methacrylate) is an important acrylic thermoplastic polymer. Poly(methyl methacrylate) is a transparent and rigid synthetic plastic. There has been growing interest in developing high performance poly(methyl methacrylate)-based nanocomposites. This article reviews a few important poly(methyl methacrylate)-based nanocomposites and composites. An extended account of the poly(methyl methacrylate) nanocomposites with carbonaceous nanofillers and fillers is given. The physical properties and how to manufacture poly(methyl methacrylate)/carbon nanotube, poly(methyl methacrylate)/carbon black, and poly(methyl methacrylate)/carbon fiber materials are appraised. The research so far shows that the mechanical, thermal, conducting, and microstructural performances improved compared with pure poly(methyl methacrylate). In order to further enhance the poly(methyl methacrylate) material performance, chemically modifying the carbonaceous fillers and chemical affinity with the polymer matrix are necessary. The main challenges here are to obtain well-dispersed, aligned, and easily processable poly(methyl methacrylate)-based composites. Poly(methyl methacrylate)-based nanocomposite applications are also reviewed in an attempt to facilitate progress in this emerging area. These materials are potential candidates in electromagnetic interference shielding, gas sensors, separation membranes, tissue engineering, and drug delivery applications.

Development of Magnetic Materials Based on Micro-Nano Particles Natural Ferrite as Microwaves Absorber Materials

Ferrite-based magnetic materials (ferrites) can be simple iron oxide compounds such as Fe2O3 or Fe3O4, and similar compounds containing other cations besides iron, such as BiFeO3, CaFe 4O7, and BaFe12O19. The solid phase of these compounds generally has varying magnetic properties, depending on the cation (A+m) which is the substitution of the iron cation (Fe+3) in its crystal structure. In addition to the magnetic properties of interest, the compound in question also has strong absorption properties in electromagnetic waves in the frequency interval of 1 - 20 GHz (microwave), which is commonly used in the world of communication and radar technology. With these properties it is possible to develop these materials for electromagnetic shielding and stealth technology applications. As a magnetic element, ferrite material requires a conductive reflector element, to form a “core - shell” or “matrix - filler” system which results in absorption properties. The research that has been developed is in the form of Fe3O4 based micro-nano magnetic powder made from natural ferrite (iron sand). The sythesized of magnetic micro-nano particles using chemical extraction-milling and coprecipitation methods. Morphology of micro-nano particles ferrites has been confirmed by using SEM and TEM. The results of measurements of absorption of microwaves using a Vector Network Analyzer showed that the ferrite nano particle powder has greater absorption power (Reflection Loss < - 20 dB) than micro particle powders with ≥ 99 % absorption in the “X-band” region. The extraction-milling method is simpler and more economical than the chemical coprecipitation method so that it is suitable to be an alternative method for producing large-scale ferrite powder.

Technical viewpoint on polystyrene/graphene nanocomposite

This review presents state-of-the-art progress in the field of polystyrene (PS)/graphene nanocomposite. Graphene is a monoatomic thick nanoallotrope of carbon. It has attracted tremendous research consideration owing to chemical functionalization aptitude and remarkable physical properties. Graphene has been used as a potential nanofiller to dramatically improve the performance of polymeric nanocomposite. PS is an important synthetic aromatic thermoplastic polymer. Graphene has been used to enhance the mechanical strength, thermal stability, electrical conductivity, and thermal conductivity of PS/graphene nanocomposite. Dispersion routes and synthetic methods of graphene and PS/graphene nanocomposite have also been reviewed. PS/graphene nanocomposites have been explored for anticorrosion, electromagnetic interference shielding, batteries, electrocatalysis, and microextraction applications. In spite of interesting developments, a lot remains to be done with regard to fundamental understanding of structure–property relationship and designing materials to operate for advanced high performance applications. This review is also concluded listing current challenges associated with processing and future perspectives of nanocomposite.

The electromagnetic shielding effectiveness of laminated fabrics using electronic printing

AbstractThis paper describes the development of laminated fabrics that contain a silver grid for electromagnetic shielding (EMS) applications. The silver grid was constructed with 0.3, 0.4, and 0.5 mm wire diameters and spacings. To reduce material costs, a solvent‐based polytetrafluoroethylene (PTFE) film, cotton woven fabric, and conductive silver paste were used to fabricate a cost‐effective EMS conductive laminated fabric successfully. Using a coaxial transmission line holder, the electromagnetic shielding effectiveness (EMSE) of various conductive laminated fabrics was measured in the 30 to 3000 MHz frequency range. The variation in the EMSE of the conductive networks with different grid shapes, grid densities, fineness values for the conductive lines, and concentrations of the silver paste on the PTFE films was evaluated. Based on optical microscopy observations and analysis, it was found that the conductive silver paste that was diluted by a high boiling point solvent comprising a mixed dibasic acid ester (DBE) could be printed on the PTFE film using a 300‐mesh screen to obtain a clear and complete mesh wire structure that was easy to coat. The results indicated that the proposed conductive laminated fabrics with the 0.3 mm silver wire dimension and spacing had a higher EMSE and electrical conductivity than those of the 0.4 and 0.5 mm wire dimensions and spacings. The results also showed that the fabrics with a 0.3 mm wire diameter and spacing with DBE dilution had a slightly lower EMSE and electrical conductivity than those of the bare PTFE films with a 0.3 mm wire diameter and spacing in the 120 to 2450 MHz frequency range. The conductive laminated fabrics with a 0.3 mm wire diameter and spacing silver electronic coating could be used for electromagnetic interference shielding applications. The conductive silver‐laminated woven fabric could also be applied to curtains, wall coverings, bedspread sets, maternity clothes, work bibs, microwave ovens, induction cookers, protective clothing, and antielectromagnetic mobile phone sets.

Ultrathin wideband slot and patch FSS elements with sharp band edge characteristics

ABSTRACT Two diverse applications of FSS as bandpass and bandstop filters with wideband and sharp band edge characteristics are investigated in this paper. The proposed design comprised of a tapered tripole element in aperture and patch type printed on either side of a dielectric material to act as bandpass and bandstop filters respectively. The structures are ultrathin in design; structures comprise two metallic layers, isolated by single thin substrates with a thickness of 0.027λ. In the case of bandpass, the structure shows a relative bandwidth (−1 dB) of 8.87% with insertion loss better than 0.2 dB at normal incidence. Whereas, in the case of bandstop, it shows 24.36% (−10 dB). Further, the parametric analysis is performed for obtaining optimal performance. Both structures in the proposed form have spectacular application in bandpass filtering (slot FSS) and electromagnetic shielding (patch FSS). Further, two design techniques are presented namely dielectric encapsulation and substrate integrated waveguide (SIW) based FSS structures to develop a periodic structure to cater the high power handling in microwave sources. Finally, a fabricated prototype along with experimental verification proves the validity of simulated results.

Tailorable Negative Permittivity of Carbon Materials Derived from Microcrystalline Cellulose at Different Carbonizing Temperature

In this work, electrical conductivity, permittivity behavior and microstructure of carbon materials derived from microcrystalline cellulose precursor at different carbonization temperature were investigated. Electrical percolation was observed with the self-constructed carbon percolative network formed. Plasma-like negative permittivity property was realized, which was well described by Drude model, resulting from the plasma oscillations of free electrons in self-constructed carbon networks. Meanwhile, magnitude and dispersion of the negative permittivity were closely associated with the carbonization temperature. This work provided a convenient way to obtain tunable negative permittivity properties with carbon materials, which have great potential in energy-storage capacitor and electromagnetic shielding applications.

An anisotropic layer-by-layer carbon nanotube/boron nitride/rubber composite and its application in electromagnetic shielding.

Multifunctional polymer composites with anisotropic properties are attracting interest as they fulfil the growing demand of multitasking materials. In this work, anisotropic polymer composites have been fabricated by combining the layer-by-layer (LBL) filtration method with the alternative assembling of carbon nanotubes (CNTs) and hexagonal boron nitride flakes (hBN) on natural rubber latex particles (NR). The layered composites exhibit anisotropic thermal and electrical conductivities, which are tailored through the layer formulations. The best composite consists of four layers of NR modified with 8 phr (parts per Hundred Rubber) CNTs (∼7.4 wt%) and four alternate layers with 12 phr hBN (∼10.7 wt%). The composites exhibit an electromagnetic interference (EMI) shielding effectiveness of 22.41 ± 0.14 dB mm-1 at 10.3 GHz and a thermal conductivity equal to 0.25 W m-1 K-1. Furthermore, when the layered composite is used as an electrical thermal heater the surface reaches a stable temperature of ∼103 °C in approx. 2 min, with an input bias of 2.5 V.

Chemical vapor deposition growth and characterization of graphite-like film

Thick graphene film can be widely used in surface protection, heat dissipation, heating devices and other fields. Here we present a study on the growth and characterization of large area continuous and patterned graphite-like films prepared on Ni foil through CVD. Effects of parameters on the material growth are studied experimentally and theoretically in detail. Thickness of the graphite-like film in this work can reach 500 nm and can be regulated by growth process. Characterization results show that the graphite-like film is formed by free stacking of large area graphene continuous films and possesses strong mechanical strength, chemical stability, good electrical conductivity and flexibility. The graphite-like film shows potential for application in metal surface protection, flexible conduction, heating and electromagnetic shielding.

An effective utilization of MXene and its effect on electromagnetic interference shielding: flexible, free-standing and thermally conductive composite from MXene-PAT-poly(p-aminophenol)-polyaniline co-polymer.

MXene and conductive polymers are attractive candidates for electromagnetic interference shielding (EMI) applications. The MXene–PAT-conductive polymer (CP) composites were fabricated by a cost-effective spray coating technique and characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. A new approach has been developed for the synthesis of exfoliated MXene. The MXene–PAT–poly(p-aminophenol)–polyaniline co-polymer composite exhibited good electric conductivity (EC) of 7.813 S cm−1. The composites revealed an excellent thermal properties, which were 0.687 W (m K)−1 thermal conductivity, 2.247 J (g K)−1 heat capacity, 0.282 mm2 s−1 thermal diffusivity and 1.330 W s1/2 m−2 K−1 thermal effusivity. The composites showed 99.99% shielding efficiency and the MXene–PAT–PANI–PpAP composite (MXPATPA) had EMI shielding effectiveness of 45.18 dB at 8.2 GHz. The reduced form of MXene (r-Ti3C2Tx) increased the shielding effectiveness (SE) by 7.26% and the absorption (SEA) was greatly enhanced by the ant farm like structure. The composites possess excellent thermal and EMI SE characteristics, thus can be applied in areas, such as mobile phones, military utensils, heat-emitting electronic devices, automobiles and radars.

Design and analysis of negative permittivity behaviors in barium titanate/nickel metacomposites

As an important supplement to the metamaterials, negative permittivity in 'natural' materials has attracted increasing attention, while some fundamental regulation mechanisms and common theoretical principles have not yet been systematically explored. In this paper, the permittivity transition is investigated along with insulator-conductor conversion in BaTiO3/Ni composite. When the Ni content in BaTiO3/Ni composites is lower than and higher than the percolation threshold, Lorentz-like and Drude-type negative permittivity behaviors is obtained, respectively. In addition, the fundamental principles of negative permittivity are discussed, especially the validity of the Kramers–Kronig relations and the relationship between the negative permittivity and the reactance characters. Further, a universal regulatory mechanism of the Drude-type negative permittivity profile is qualitatively analyzed. Negative permittivity and negative permeability are achieved simultaneously in BaTiO3/Ni composites with 35.56 vol% of Ni loading, which show potential application in electromagnetic wave absorption and shielding.

Ultra-broadband and wide-angle absorption based on 3D-printed pyramid

This paper proposes a 3D-printed pyramidal absorber, which comprises of the printing filaments, carbon-loaded Acrylonitrile Butadiene Styrene (ABS). This ABS has certain absorption effects, and shows simple and rapid prototyping characteristics. Here, we experimentally demonstrated the directly printed pyramidal absorber showing the absorption more than 90% within the frequency range from 5.3 to 18 GHz. The incident energy at the low and high peak frequencies are mostly attenuated by λ/4 resonances, corresponding to the wavelength of λ/4 and 3λ/4 separately. Distinct from the flat absorber, the pyramidal structure and absorbent take synergistic effects for broadband absorption. Additionally, the pyramid maintained its absorption bandwidth within quite a wide incident angle, 50° for transverse electric (TE) polarization and 60° for transverse magnetic (TM) polarization. It is expected that the proposed pyramidal absorber has great potential for application in radar cross section reduction and electromagnetic shielding.

Dielectric Properties and Electrical Percolation in MnFe2O4/Epoxy Resin Composites

Broadband dielectric properties of epoxy composites containing the different additions of manganese ferrite (MnFe2O4) with two spherical particle sizes (28 and 60 nm) are studied in the wide temperature range from 150 to 500 K. The percolation thresholds in such systems are 30 and 29.3 vol% for small and large MnFe2O4 particles, respectively. The small difference in the percolation threshold value is related to a better distribution of larger nanoparticles. Composites above the percolation threshold are appropriate candidates for electromagnetic shielding applications. Above 380 K, the electrical conductivity is typical for all composites, both below and above the percolation thresholds due to the electrical transport in the polymer matrix. The activation energy strongly decreases with MnFe2O4 concentration indicating that the electrical transport occurs simultaneously in both MnFe2O4 and epoxy matrix subsystems.

Preparation and characterization of polylactic acid/polyaniline/nanocrystalline cellulose nanocomposite films

Polylactic acid (PLA) serves as an ideal matrix for preparing electrically conductive materials for electrode, electromagnetic shielding and functional biological material application. Here, an environmentally friendly PLA/polyaniline (PANI)/nanocrystalline cellulose (NCC) nanocomposite film was prepared. Effects of NCC loadings on the rheological behavior of PLA/PANI/NCC suspensions and the microscopic, thermal, mechanical and conductive properties of nanocomposite films were investigated. Results revealed that PLA was wrapped with PANI particles and NCC was uniformly distributed in the obtained nanocomposite films. The PLA/PANI/NCC films exhibited an electrical conductivity of up to 2.16 S∙m−1 with 1% NCC dosage. Besides, the viscosity and viscoelasticity of the PLA/PANI/NCC suspensions were decreased and the dispersion stability of the suspensions was improved with the incorporation of NCC. Furthermore, the mechanical strength of PLA/PANI/NCC nanocomposite films was significantly improved with the reinforcement effect of NCC. In presence of 4% NCC loading, the tensile strength (TS) and tensile modulus (TM) of PLA/PANI/NCC films had an increase of 38.1% and 89.1%, respectively, while the elongation at break (Eb) exhibited a decrease of 27.3%, as compared to that of PLA/PANI films. These results demonstrated that the as-prepared PLA/PANI/NCC nanocomposite film may have the potential to be used as a bio-based electrically conductive material.

Broadband graphene‐based metasurface solar absorber

AbstractWe presented broadband solar absorber using graphene‐based pyramid‐shaped metasurface structure. The proposed design is analyzed for its absorption characteristics from 100 THz to 1000 THz frequency range (infrared, visible, and ultraviolet region) in term of geometrical parameters of the design. Results in term of reflectance and absorption are presented for pyramidal metasurface design and rectangular metasurface design. The results indicate that the absorption of proposed pyramid graphene‐based metasurface design is over 67.4% for 100 to 430 THz across the infrared region, 87.3% for 431 to 770 THz across the visible region and 89.3% for 770 to 1000 THz across the ultraviolet region. The proposed design provides broadband absorption response which is applicable in energy harvesting and electromagnetic shielding applications.