Enhanced electromagnetic shielding property of cf/mullite composites fabricated by spark plasma sintering

Aiming to prepare high-performance electromagnetic interference (EMI) shielding materials, chopped carbon fibers were incorporated into mullite ceramic matrix via rapid prototyping process of spark plasma sintering (SPS). Results indicate that C_f/mullite composites with only 1 wt% of carbon fibers exhibit highest shielding effectiveness (SE_T) over 40 dB at a small thickness of 2.0 mm, showing great advantages both in terms of performance and thickness compared with many mature carbon/ceramic composites. The high EMI shielding properties mainly depend on two mechanisms of absorption and reflection in this present work. The enhanced absorption and reflection of electromagnetic wave are ascribed to the promotional electrical conductivity arising from the formation of conductive network by introduction of carbon fibers. Regarding enhanced electrical conductivity, notable intensified interfacial polarization on a large number of interfaces between mullite matrix and carbon fibers is also the key factor to the improved absorption, which makes absorption play a dominant role in the significant improvement of EMI SE_T. The C_f/mullite composites with excellent EMI shielding properties and thin thickness show great potential application as EMI materials.     

Flexible graphene/polymer composite films in sandwich structures for effective electromagnetic interference shielding

Multilayer graphene/polymer composite films with good mechanical flexibility were fabricated into paraffin-based sandwich structures to evaluate electromagnetic interference (EMI) shielding. Experimental results showed the relationship between electrical properties and shielding performance, demonstrating that electrical properties are significant factors in EMI shielding. Calculation based on electrical conductivity of the composite films was carried out to investigate the fundamental mechanisms of absorption, reflection and multiple-reflections for the polymeric graphene composite films. Both experimental and calculated results indicate that reflection is the dominating shielding mechanism for the as-fabricated polymeric graphene films. The optimization of thickness, skin depth and electrical conductivity in the shielding materials could be highly significant in achieving enhanced EMI shielding. Further improvement in absorption shielding has been achieved by increasing the shielding thickness in order to enhance the overall shielding performance. The optimized shielding effectiveness up to 27 dB suggested effective shielding of the composite films. The implication of the mechanisms for optimizing shielding performance demonstrates significant fundamental basis for designing high-performance EMI shielding composites. The results and techniques also promise a simple and effective approach to achieve light-weight graphene-based composite films for application potentials in EMI shielding coatings.     

Modeling for the electromagnetic properties and EMI shielding of Cf/mullite composites in the gigahertz range

The electromagnetic properties and EMI shielding effectiveness of C_f/mullite composites via the spark plasma sintering were intensively investigated in the gigahertz range (8.2–12.4 GHz). Experimental results have revealed excellent electromagnetic properties and a high value of EMI shielding effectiveness (nearly 40 dB) for C_f/mullite composites with 1.65 vol% carbon fillers at thickness of 2 mm. We quantitatively characterize the contributions of microstructural features to overall EMI shielding effectiveness using a micromechanics-based homogenization model. The EMI shielding effectiveness enhances with respect to the C_f volume concentration before the threshold. The increasing trend of EMI shielding effectiveness with respect to AC (alternating current) frequency can be attributed to enhanced conductivity at high gigahertz range. It is demonstrated that filler and frequency dependent interface effects are essential to obtain excellent electromagnetic properties of C_f/mullite composite. The present research can provide guidances for the design of ceramic-based composites applied in high-temperature EMI shielding devices.     

Highly conductive and high-strength carbon nanotube film reinforced silicon carbide composites

Film formed by carbon nanotubes is usually called carbon nanotube film (CNT_f). In the present study, CNT_f fabricated by floating catalyst method was used to prepare CNT_f/SiC ceramic matrix composites by chemical vapor infiltration (CVI). Mechanical and electrical properties of the resulting CNT_f/SiC composites with different CVI cycles were investigated and discussed, and the results revealed that the CNT_f has a good adaptability to CVI method. Tensile test demonstrated an excellent mechanical performance of the composites with highest tensile strength of 646 MPa after 2 CVI cycles, and the strength has a decline after 3 CVI cycles for an excessively dense matrix. While, the elastic modulus of the composite increased with the CVI cycles and reached 301 GPa after 3 CVI cycles. Tensile fracture morphologies of the composites were analyzed by scanning electron microscope to study the performance change laws with the CVI cycles. With SiC ceramic matrix infiltrated into the CNT_f, enhanced electrical conductivity of the CNT_f/SiC composite compared to pure CNT_f was also obtained, from 368 S/cm to 588 S/cm. Conductivity of the SiC matrix with free carbon forming in the CVI process was considered as the reason.     

High performance EMI shielding applications of Co0.5Ni0.5CexSmyFe2-x-yO4 nanocomposite thin films

The fast development in the compact and wearable opto-electronics devices need a high-performance electromagnetic (EM) shielding materials that are shows a unique feature like lightweight and flexible in characteristics that increase the problems of electromagnetic pollution. At present technological aspects, the absorption predominant microwave shielding materials are gain the huge demand for preventing the major problems of electromagnetic interference over the modern electronic devices as well as environment. In the report we presents synthesis of multifunctional composite thin film material that adequately includes the exceptional EMI shielding, mechanical flexibility and magnetic properties of composite thin film for portable and wearable electronic devices which could be operated at GHz frequencies. The Co_0.5Ni_0.5Ce_xSm_yFe_2-x-yO₄ (denoted as CNCSF) its scanning electron microscopy (SEM) micrographs revel the fact that the samples highly agglomerated characteristics features of the prepared thin film samples, this agglomerated structure of the composite film will enhance the EMI shielding performances and strain sensing responses. Further, the prepared thin films were subjected to characterized XRD and Raman spectroscopic techniques to analyse the crystallinity and different functional groups present in the prepared thin films. By doping of samarium and cesium nanoparticles into the Co_0.5Ni_0.5Fe_2-x-yO₄ forms the superior conducting islands and enhances the dielectric and magnetic properties of the composite thin films. Owing to the improved dielectric and magnetic properties this x,y = 0.02 ferrites based thin film nanocomposite with the 0.4 mm thickness exhibit the absorption predominated outstanding electromagnetic shielding responses in the order of ?23 dB which is almost equal to 99.67% of shielding efficiency in broad band microwave frequencies. Furthermore, these material-based nanocomposite shields show exceptional stability in EMI shielding efficiency under the different mechanical stretching strains. In addition to superior excellent shielding material, this material-based nanocomposite thin film shows an exceptional strain sensing behaviour, which evident that multifunctional applications of this ferrites based thin material. Owing to the all-unique properties like light weight, flexibility, outstanding EMI-SE and excellent strain sensing behaviour, these ferrites-based material thin film could be employed in flexible and fortable electronic devices as crafty jacket on shield.     

Theoretical prediction and experimental verification on EMI shielding effectiveness of dielectric composites using complex permittivity

The evaluation and optimization of EMW absorbing properties have been widely studied, but little research focused on EMI shielding properties predicted by complex permittivity. Based on the transmission-line theory, shielding effectiveness (SE) of a dielectric composite was evaluated by the reflection coefficient (Г) and transmission coefficient (T) which were calculated by the complex permittivity. SiC_f/SiCN composites containing different content of CVI SiCN matrix are attractive for their tunable dielectric properties, which may vary from EMW absorption to EMI shielding. Therefore, SiC_f/SiCN composites are typical dielectric composites used for experimental verification, and the results indicate that the dielectric composites without CVI SiCN phase have good EMW absorbing properties, while they exhibit good EMI shielding effectiveness with CVI SiCN phase. This work builds a relationship between the EMI shielding effectiveness and the complex permittivity, and obtains the optimized complex permittivity for excellent EMI shielding effectiveness.     

Roll-to-roll processable MXene-rGO-PVA composite films with enhanced mechanical properties and environmental stability for electromagnetic interference shielding

MXene films promise potential electromagnetic interference (EMI) shielding materials, but poor scalable processability, environmental instability, and weak mechanical properties severely restrict their applications. Herein, we engineer the large-area, high-performance, and compact nacre-like MXene-based composite films through cooperative co-assembly of Ti₃C₂T_X MXene and reduced graphene oxide (rGO) in the presence of polyvinyl alcohol (PVA). The resulting MXene-rGO-PVA composite films benefit from enhanced bonding strength and extra chain bridging effect of linear PVA molecules enriched with hydroxyl groups. Therefore, the composite film achieves high tensile strength (～238 MPa) and toughness (～1.72 MJ m^?3) while having high conductivity of ～32 S cm^?1. A significant EMI shielding effectiveness (41.35 dB) is also demonstrated, with an excellent absolute shielding effectiveness of ～20,200 dB cm² g^?1 at only 12-μm thickness. Moreover, due to the synergistic effect of multiple components, the composite films maintain a stable EMI shielding performance in harsh environments (sonication, hot/cold annealing, and acid solution) with mechanical properties that fluctuate only within 10% compared to the original film. More importantly, commercial polyethylene terephthalate release liner can be applied for the film coating, facilitating continuous roll-to-roll production of large-area films and future applications.     

Effect of microstructure induced by microcellular injection molding on electromagnetic interference shielding properties

Preparing lightweight and versatile products is the unremitting goal of industry to save resources and energy. Lightweight carbon fiber reinforced polypropylene (CF/PP) composite foams with high-performance electromagnetic interference (EMI) shielding materials were fabricated by microcellular injection molding (MIM) technology. The average length and distribution of CF in CF/PP composite foams were examined. Thanks to the introduction of foaming process, the average CF length of composite foams was 33.98% longer than that of solids, which effectively enhanced the electrical conductivity and EMI shielding properties. The effect of shot size, gas content, and injection rate on the electrical conductivity and EMI properties was investigated. With melt shot size of 2/3 of the cavity volume, gas content of 0.5 wt% N₂ and injection rate of 100 mm/s, optimal cellular structure of the composite material was obtained. The EMI shielding effectiveness (SE) reaches 36.94 dB, which is the highest value achieved by using MIM technology to the best of the authors' knowledge. In addition, the mechanical properties of cellular structure can still maintain good values, with the tensile strength and impact strength improved by 15.3% and 14.03%, respectively.     

Strong and Flexible Carbon Fiber Fabric Reinforced Thermoplastic Polyurethane Composites for High‐Performance EMI Shielding Applications

Electromagnetic shielding materials play a significant role in solving the increasing environmental problem of electromagnetic pollutions. The commonly used metal‐based electromagnetic materials suffer from high density, poor corrosion resistance, and high processing cost. Polymer composites exhibit unique combined properties of lightweight, good shock absorption, and corrosion resistance. In this study, a novel high angle sensitive composite is fabricated by combining carbon fiber (CF) fabric with thermoplastic polyurethane elastomer (TPU). The effect of stacking angle of CF fabric on EMI shielding performance of composite is studied. When the stacking angle of CF fabric changed, the electromagnetic interference (EMI) shielding effectiveness (SE) of CF fabric/TPU composite can reach a maximum of 73 dB, and the tensile strength can reach 168 MPa. In addition, the composite has anisotropic conductivity, which is conductive along the plane direction and nonconductive along the thickness direction. Moreover, the CF fabric/TPU composite manifests exceptional EMI‐SE/density/thickness value of 383 dB cm² g^?1, which is higher than most of current EMI shielding composites reported in literature. In summary, CF fabric/TPU composite is an excellent EMI shielding material that is lightweight, highly flexible, and mechanically robust, which can be applied to the field of aerospace and some intelligent electronic devices.     

Fine-grained and electrically conductive NdB6/SiO2: A promising electromagnetic interference shielding material with good thermal and mechanical properties

Searching for thermal conductive materials with high electromagnetic interference (EMI) shielding effectiveness (SE) is the key to protect electronic equipment against electromagnetic pollution and excess heat emission. Herein, NdB₆/SiO₂ bulks with high EMI SE and thermal conductivity which also exhibit good mechanical properties were prepared by liquid phase sintering (LPS). The NdB₆/SiO₂ bulk prepared by LPS at 1550 °C has fine grain-size, which is beneficial to improving mechanical property and EMI shielding performance. It exhibits high conductivity of 1.47 × 10⁴ S/cm, high EMI SE of 55.1 dB in K band, and high thermal conductivity of 37.9 W/m K. It also possesses flexural strength of 266 MPa and Vickers hardness of 14.8 GPa. Thus, NdB₆/SiO₂ composite ceramics are promising candidates for EMI shielding with good heat dissipation and mechanical load-bearing capabilities.     

Ti3C2Tx-coated diatom frustules-derived porous SiO2 composites with high EMI shielding and mechanical properties

Effective electromagnetic interference (EMI) shielding materials have garnered substantial interest for their efficacy in attenuating electromagnetic wave energy, ensuring data confidentiality, ensuring the operational stability of fragile electronic systems. To begin, artificially cultured diatom frustules (DF)-derived porous silica (DFPS) skeletons were constructed as templates in this study. Porous ceramics hot-pressed at 800 °C displayed a high compressive strength with a high specific surface area due to their three-dimensional (3D) multilayered and porous structures. Then, mechanically robust Ti₃C₂T_x/DFPS composites with exceptional EMI shielding performance were fabricated by immersing porous DF-based ceramics into Ti₃C₂T_x solutions and annealing in an argon environment to increase the materials’ shielding efficiency (SE). The EMI SE of composites hot-pressed at 800 °C achieved the maximum EMI SE of 43.2 dB in the X-band and a compressive strength of 67.5 MPa, establishing a hitherto unreported balance of mechanical characteristics and shielding performance. Prolonged transmission paths, multiple dissipation, scattering and reflection of electromagnetic energy were achieved using a well-maintained hierarchical porous silica framework decorated with MXene, with adsorption caused by surface MXene serving as the primary shielding mechanism for the composites. Due to their superior overall performance, MXene/DFPS EMI shielding composites have a bright future in the aircraft sector as delicate electronic device components.     

Theoretical and experimental studies on EMI shielding mechanisms of multi-walled carbon nanotubes reinforced high performance composite nanofibers

Electrically conductive composite nanofibers of polyvinylpyrrolidone (PVP) filled with multi-walled carbon nanotubes (MWCNTs) were prepared by electrospinning process. The complex permittivity and electromagnetic interference shielding effectiveness (EMI SE) of all composite nanofibers were measured in the X band frequency range 8.2–12.4 GHz. The electrical conductivity, real and imaginary part of permittivity, and EMI shielding behaviors of the composite nanofibers were reported as function of MWCNTs concentration. Electrical conductivity of MWCNTs/PVP composite nanofiber followed power law model of percolation theory having a percolation threshold ?_c = 0.72 vol% (~1 wt.%) and exponent t = 1.71. The total EMI SE of MWCNTs/PVP composite nanofibers increased up to 42 dB mainly base on the absorption mechanism. The EMI SE measured from experiments was also compared with the approximate value calculated from theoretical model. The obtained theory results confirmed that the selected model presented acceptable performance for evaluating the involved parameters and prediction of the EMI SE of composite nanofibers. The ability of the theoretical model to predict the EMI shielding by reflection and absorption was found to be a function of the frequency, thickness, permittivity, and conductivity.     

Electromagnetic shielding properties of carbon‐rich chemical vapor infiltration‐prone silicon carbide matrix composites

This study focuses on the electromagnetic interference shielding effectiveness (EMI SE) of SiC nanowire/SiC ceramic composites (SiC_nw/SiC) manufactured by chemical vapor infiltration of SiC_nw aerogels with carbon‐rich SiC. The total EMI SE of a 1.0 mm thick ceramic composite specimen with density of only 2.68 g/cm³, was found to be 43‐44 dB, which indicates an excellent EM shielding capability of the ceramic composite corresponding to blocking of 99.99% of the incident EM signal. It was found that the carbon‐rich CVI‐SiC matrix possess excellent EM shielding properties, therefore, the CVI‐SiC CMCs themselves possess an excellent EM shielding property as a result of the carbon‐rich SiC matrix.     

Electrical conductivity and electromagnetic interference shielding effectiveness of nano-structured carbon assisted poly(methyl methacrylate) nanocomposites

Nanostructured carbon-based polymeric nanocomposites are gaining research interest because of their cost-effectiveness, lightweight, and robust electromagnetic interference (EMI) shielding performance. Till now, it is a great challenge to design and fabricate highly scalable, cost-effective nanocomposites with superior EMI shielding performance. Herein, highly scalable EMI shielding material with tunable absorbing behaviors comprising of low-budget ketjen black (K-CB) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been prepared using simple solvent assisted solution mixing technique followed by hot compression technique. The morphological investigation revealed the homogeneous distribution of K-CB and strong interfacial interaction in PMMA matrix, which validated the strong reinforcement and other intriguing properties of the nanocomposites. The PMMA nanocomposites showed a low percolation threshold (2.79 wt%) and excellent electrical conductivity due to the formation of 3D conductive network like architecture within the polymer matrix. Specifically, the 10 wt% K-CB nanocomposite possessed a superior EMI shielding performance of about 28 dB for X-band frequency range. Further, a huge change in EMI shielding performance of PMMA nanocomposites is observed with varying thickness. The brand new K-CB decorated PMMA nanocomposites are expected to open the door for next-generation cost-effective EMI shielding materials for academic and industrial applications.     

High‐performance electromagnetic interference shielding material based on an effective mixing protocol

A facile and economic method is developed for the fabrication of new lightweight materials with high electromagnetic interference (EMI) shielding performance, good mechanical properties and low electrical percolation threshold through melt mixing. Electrical properties, DC conductivity, EMI shielding performance and mechanical properties of poly(trimethylene terephthalate) (PTT)/multiwalled carbon nanotube (MWCNT) nanocomposites with varying filler loading of MWCNTs were investigated. High‐resolution transmission electron microscopy was used to determine the distribution of MWCNTs in the PTT matrix. The newly developed nanocomposites show excellent dielectric and EMI shielding properties. Theoretical electrical percolation threshold was achieved at 0.21 wt% loading of MWCNTs, due to the high aspect ratio and the three‐dimensional network formation of MWCNTs. Experimental DC conductivity values were compared with those of theoretical models such as the Voet, Bueche and Scarisbrick models, which showed good agreement. The PTT/3% MWCNT composite showed an EMI shielding value of ～38 dB (99.99% attenuation) with a sample thickness of 2 mm. Power balance was used to determine the actual contribution of reflection, absorption and transmission loss to the total EMI shielding value. The nanocomposites showed good tensile and impact properties and the composite with 2% MWCNTs exhibited an improvement in tensile strength of as much as 96%. © 2018 Society of Chemical Industry     

Electromagnetic interference shielding effectiveness of hybrid multifunctional Fe3O4/carbon nanofiber composite

Electromagnetic interference shielding effectiveness (EMI SE) of multifunctional Fe₃O₄/carbon nanofiber composites in the X-band region (8.2–12.4 GHz) is studied. Here, we examine the contributing effects of various parameters such as Fe₃O₄ content, carbonization temperature and thickness on total shielding efficiency (SE_total) of different samples. The maximum EMI SE of 67.9 dB is obtained for composite of 5 wt.% Fe₃O₄ (0.7 mm thick) with the dominant shielding by absorption (SE_A) of electromagnetic radiation. The enhanced electromagnetic shielding performance of Fe₃O₄/carbon nanofiber composites is attributed to the increment of both magnetic and dielectric losses due to the incorporation of magnetite nanofiller (Fe₃O₄) in electrically conducting carbon nanofiber matrix as well as the specific nanofibrous structure of carbon nanofiber mats, which forms a higher aspect ratio structure with randomly aligned nanofibers. Furthermore, we prove that the addition of elastomeric polydimethylsiloxane (PDMS) as a coating for carbon nanofiber composite strengthens the composite structure without interfering with its electromagnetic shielding efficiency.     

SiC encapsulated Fe@CNT ultra-high absorptive shielding material for high temperature resistant EMI shielding

Carbon nanotubes (CNTs) decorated with ferromagnetic materials have promising potential in electromagnetic interference (EMI) shielding applications. In this work, CNT sponges with increasing density were fabricated by filling them with magnetic Fe nanowires of mutative filling ratios via chemical vapor deposition (CVD). Results indicated that Fe@CNT composites with the highest density endowed the most remarkable average SE_T value of 70.01 dB (more than 99.99999% absorption), showing an ultra-high EMI shielding performance. However, the susceptibility to oxidation of carbon materials has restricted its further development in high-temperature EMI shielding applications. Therefore, the Fe@CNT composites were encapsulated by silicon carbide (SiC) with satisfactory oxidation resistance. Thereafter, the average SE_T value of SiC encapsulated a higher density Fe@CNT sponge decreased to an adequate value of 36.48 dB due to the huge loss of electrical conductivity. However, the SE_T value of it only dropped by about 1.20 as the temperature went up from 25 to 600 °C, demonstrating an excellent stability under high temperature conditions. As a proof of concept, the Fe@CNT/SiC composites with adequate EMI shielding performance and satisfactory oxidation resistance suggest its prospect in high temperature resistant EMI shielding.     

Magnetite/graphene oxide/Prussian blue composite with robust effectiveness for electromagnetic interference shielding

Considering the promising efficiency of composites, in the current study, a graphene oxide (GO)-magnetite-Prussian blue (PB) composite material was prepared. The composite exhibited electrical conductivity, magnetic permeability, and permittivity nature, and was evaluated using electromagnetic interference (EMI) shielding studies. GO was developed by the Hummer's method, ferrite (Fe₃O₄) was incorporated by the sol-gel method, and PB was introduced in the mixture by an in-situ process. The fabricated samples were studied by X-ray diffraction, Raman Spectroscopy, Fourier-transform infrared spectroscopy along with EMI shielding efficiency (SE) evaluation. The SE of ?71.66 dB of reflection losses was measured at a frequency of 1.5 MHz. The GO/Fe₃O₄/PB composite provided the best results for the detection in the 1–18 MHz frequency range because of its excellent electric and magnetic properties. The obtained results demonstrated that the GO/Fe₃O₄/PB composite has promising potential applications in EMI shielding.     

Synthesis and tunable electromagnetic shielding and absorption performance of the three-dimensional SiC nanowires/carbon fiber composites

Silicon-carbide nanowires (SiCnws) have been considered as dielectric loss materials for application in the field of electromagnetic wave (EMW) attenuation. In this study, SiCnws/carbon fiber (CF) composites were fabricated using precursor infiltration and pyrolysis process for the in-situ growth of SiCnws. The SiCnw fraction of the SiCnws/CF composites could be adjusted using various catalysts. At a small SiCnw fraction (38 wt%), the composites exhibited excellent EMW absorption performance with the minimum reflection loss of ? 18.3 dB when their thickness was only 1.2 mm and can cover the entire X and Ku bands by adjusting the material thickness. They transformed from EMW absorption performance to electromagnetic interference (EMI) shielding property with the increase in SiCnw fraction from 38 wt% to 73 wt%, reaching an EMI shielding effectiveness of 31.25 dB. In addition, the density of the SiCnws/CF composites was only 0.31–0.41 g/cm³, and their compressive strength can reach 0.61–0.99 MPa with excellent high-temperature stability. Therefore, the SiCnws/CF composite presents a promising EMW absorption and EMI shielding material that can be applied in harsh environments.     

2D Ti3C2Tx MXene/aramid nanofibers composite films prepared via a simple filtration method with excellent mechanical and electromagnetic interference shielding properties

Electromagnetic shielding (EMI) materials are becoming more and more important because of the increasingly serious radiation pollution. The preparation of high mechanical strength, ultrathin, lightweight, flexible materials with excellent EMI shielding performance have so far been elusive. Here, we try to prepare an ultrathin, lightweight and flexible film with excellent EMI shielding performance using one-dimensional aramid nanofibers (ANFs) and two-dimensional few-layered Ti₃C₂T_x through a simple filtration method. The ultimate tensile strength and strain of the film are up to 116.71 MPa and 2.64%. The EMI shielding effectiveness and the specific EMI shielding efficiency are 34.71 dB and 21971.37 dB cm² g⁻¹, which will be no recession after 1000 times bending. Our results show that a practical EMI shielding material with excellent performances has been successfully prepared, which will be widely applied in wearable electronics, robot joints, and precision instrument protection and so on.