Electromagnetic Interference Shielding Materials Research Articles

Reduced Graphene Oxide/MXene Composite Foam with Multilayer Structure for Electromagnetic Interference Shielding and Heat Insulation Applications

The electromagnetic interference (EMI) shielding performance of reduced graphene oxide (rGO) foam is restricted to its poor conductivity and macro‐monotonic structure. In this work, highly conductive MXene nanosheets are introduced into graphene oxide (GO) solution and multilayer structures were designed to improve the EMI shielding performance of graphene foam. The multilayer rGO/MXene composite foam shows an excellent EMI shielding effectiveness of more than ≈28 dB in C and ≈35 dB in X band. Meanwhile, it reveals an outstanding heat insulation performance equaling to air (0.025 W m−1 K). The macro multilayer and microporous structure plays a prominent role in the EMI shielding and heat insulation performance. This work provides valuable ideas for designing multifunctional EMI shielding materials for the next generation of smart electronic devices.

Sustainable bacterial cellulose reinforced carbon nanotube buckypaper and its multifunctionality for electromagnetic interference shielding, Joule heating and humidity sensing

There is currently enormous and growing demand for sustainable, high-performance and multifunctional electromagnetic interference (EMI) shielding materials for wearable devices. In this work, sustainable resources bacterial cellulose (BC) was selected as reinforced filler of carbon nanotubes (CNT) buckypaper (BP) due to its excellent mechanical strength. A new kind of multifunctional BC reinforced BP (BC-BP) was fabricated through the facile vacuum assisted filtration method. The obtained BC-BP with interpenetrating structure showed outstanding mechanical properties and high electrical conductivity simultaneously. The BC-BP with 50 wt% BC (50%BC) exhibited the tensile strength of 55.78 MPa, the fracture strain of 11.67%, and the electrical conductivity of 16.67 S/cm. The corresponding EMI shielding efficiency (EMI SE) and the specific EMI SE value (SSE/t) of the 50%BC with the thickness of 36 μm was 24.01 dB and 9074 dB⋅cm2/g in the C-band range, respectively. Moreover, the 50%BC also exhibited excellent thermal conductivity (TC) of 7.39 W/mK, Joule heating (124 °C at 6 V), and humidity sensing performance of high sensitivity (10.306%/% RH) in the wide relative humidity range (5–90% RH). In addition to EMI shielding, BC-BP also showed its potential application in the management and monitoring of temperature and humidity. This work provides a new strategy to prepare sustainable, high-performance and multifunctional BC-based EMI shielding material for wearable devices.

Absorption dominated high-performance electromagnetic interference shielding epoxy/functionalized reduced graphene oxide/Ni-chains microcellular foam with asymmetric conductive structure

In order to develop high-performance electromagnetic interference (EMI) shielding materials for the increasingly complex electromagnetic (EM) environment, in this work, the epoxy/functionalized reduced graphene oxide/Ni-chains microcellular foams with asymmetrical conductive structure (a-EP/f-RGO/Ni-chains microcellular foams) are prepared through a thermal compressing method and then followed by a supercritical carbon dioxide (scCO2) foaming process. Benefiting from the construction of asymmetrical conductive structure which is assembled from the f-RGO-rich layer and Ni-chains-rich layer, the a-EP/f-RGO/Ni-chains microcellular foam with 5 vol% f-RGO and 5 vol% Ni-chains content exhibits better electrical conductivity of ∼10−1 S/m and higher EMI shielding effectiveness (EMI SE) of 40.82 dB in X-band compared with the homogeneous conductive structured EP/f-RGO/Ni-chains (h-EP/f-RGO/Ni-chains) microcellular foam in same filler content. In addition, the maximum difference of reflection coefficient (R) up to ∼0.5 is achieved by actively regulating the EMI shielding process from reflection-absorption to absorption-reflection-reabsorption in different directions of EM wave incidence on the foams. Moreover, the compressive strength of microcellular foam is up to 24.58 MPa. Combined with excellent EMI shielding property and outstanding compressive property, the a-EP/f-RGO/Ni-chains microcellular foams prepared in this work display significant application advantages as high-performance EMI shielding materials.

Stretchable polymer composite film based on pseudo-high carbon-filler loadings for electromagnetic interference shielding

Polymer composites with carbon-based filler (C-filler) are regarded as promising alternatives for flexible and stretchable electromagnetic interference (EMI) shielding materials. However, the poor mechanical properties caused by high-loadings largely hinders their practical applications, especially for the film. Herein, a class of pseudo-high C-filler (PHCF) composite films are constructed by introducing lean C-filler polymer phase on both sides of the high C-filler polymer phase. Not only does conductive structure of the high C-filler phase not transform, but the lean C-filler phase serves as both absorbing microwaves and supporting function. Strong interfacial compatibility and multi-level “zigzag” cracks synergistically enhance the mechanical stretchability with elongation at break of 200 ± 8%. Notably, its EMI shielding effectiveness reaches 31.8 dB with enhanced absorptivity (>0.2). Further, EMI shielding performance remains reliable after bending and stretching. This work offers a regulation strategy to upgrade EMI shielding materials for burgeoning stretchable, wearable and mini electronics.

The Reinforced Electromagnetic Interference Shielding Performance of Thermal Reduced Graphene Oxide Films via Polyimide Pyrolysis.

In this work, thin reduced graphene oxide (GO) composite films were fabricated for electromagnetic interference (EMI) shielding application. High solid content GO slurry (7 wt %) was obtained by dispersing GO clay in polymer solution under high-speed mechanical stirring. A composite film with varied thickness (10–150 μm) could be fabricated in pilot scale. After an optimized thermal annealing procedure, the final product showed good conductivity, which reached 500 S·cm–1. The thin sample (thickness < 0.1 mm) containing 10% polymer showed an enhanced EMI shielding performance of 55–65 dB. The outstanding EMI shielding efficiency as well as good suppleness and industrialized potential of thermal reduced graphene oxide polymer composite films could make a progress on their application in flexible devices as an EMI shielding material.

An Ultrastrong and Antibacterial Silver Nanowire/Aligned Cellulose Scaffold Composite Film for Electromagnetic Interference Shielding.

Constructing multifunctional electromagnetic interference (EMI) shielding films with superior mechanical strength has sparked a lot of interest in the fields of wearable electronics. In this work, the conductive silver nanowires (AgNWs) were synthesized and impregnated into the highly aligned cellulose scaffold (CS) fabricated by wood delignification followed by hot-pressing and polydimethylsiloxane (PDMS) dipping processes to obtain the outstanding EMI shielding cellulosic film (d-AgNWs@CS-PDMS). The consecutively conductive pathway of AgNWs was constructed in the microchannels of the CS as a result of the hydrogen bonding between AgNWs and cellulose fibers, which is conducive to the reflection of incident EM waves. The higher degree of nanofiber alignment and the compact conductive network were improved by densification upon hot pressing, which endows the composite film with striking mechanical properties (maximum tensile strength of 511.8 MPa) and superb EMI shielding performance (shielding effectiveness value of 46 dB with a filler content of 21.6 wt %) at the X band (8.2-12.4 GHz). Moreover, the existence of an intensive AgNWs network and the introduction of the PDMS layer improve the hydrophobicity and antibacterial activity of the composite film, avoiding serious health concerns in the long-term wearing. These results demonstrate that the obtained d-AgNWs@CS-PDMS composite film has high potential as an EMI shielding material used for wearable devices.

MXene/Polylactic Acid Fabric-Based Resonant Cavity for Realizing Simultaneous High-Performance Electromagnetic Interference (EMI) Shielding and Efficient Energy Harvesting.

Proliferation in telecommunications and integrated/intelligent devices entails an intense concern for electromagnetic interference (EMI) shielding and versatility. It remains an activated passion to launch infusive EMI shielding materials integrated with self-powered peculiarities. Herein, a double-layered MXene/polylactic acid (PLA) fabric resonance cavity (D-MPF-RC) comprised of two MXene/PLA fabrics (MPFs) with alternating MXene and PLA structures that are separated by a poly(tetrafluoroethylene) (PTFE) frame is developed. The D-MPF-RC achieved 48.5 and 74.8% improvement in SET and SEA, and 24.6% reduction in SER by introducing the double-layered structure and increasing the resonance cavity (RC) distance without varying the material composition and cost. A high shielding efficiency (SE) of 92.3 dB was obtained at an RC distance of 6 mm owing to the synergetic effects of multiple reflections and destructive EM wave interference. The tribopolarity difference between PLA and MXene and the RC structure made the D-MPF-RC a readily available triboelectric nanogenerator (TENG) that could convert mechanical energy into electricity. The D-MPF-RC TENG demonstrated an open-circuit voltage of 88 V and achieved a peak power density of 35.4 mW m-2 on a 6.6 MΩ external resistor, which made it possible to charge capacitors and serve as a self-powered tactile sensor. This report offers new insights into the design of high-performance EMI shielding shields with a resonance cavity and proposes a feasible pathway to integrate them with energy harvesting capabilities.

Electrospun TaC/Fe3C–Fe carbon composite fabrics for high efficiency of electromagnetic interference shielding

Electromagnetic (EM) waves usually interfere with the normal use of electric devices leading to the necessity of developing electromagnetic interference (EMI) shielding materials with light weight and strong reflection ability. Innovative carbon-based materials incorporated with conductive and magnetic fillers have aroused wide concern. Herein, we fabricated TaC/Fe3C–Fe carbon composite fabrics via electrospinning technology and high-temperature pyrolysis, which exhibited low density (0.34 g cm-3), excellent electrical conductivity (15.4 S cm-1), and good saturation magnetization (13.3 emu g-1). By investigating the optimum mass ratio of Ta and Fe, the maximum EMI shielding performance of 46.4 dB could be achieved with a thickness of 0.18 mm. And the loss mechanism was mainly based on reflection. It is expected to become a potential EMI shielding material in some commercial applications.

Electromagnetic Interference Shielding with 2D Copper Sulfide.

Electronic devices in highly integrated and miniaturized systems demand electromagnetic interference shielding within nanoscale dimensions. Although several ultrathin materials have been proposed, satisfying various requirements such as ultrathin thickness, optical transparency, flexibility, and proper shielding efficiency remains a challenge. Herein, we report an ultrahigh electromagnetic interference (EMI) SSE/t value (>106 dB cm2/g) using a conductive CuS nanosheet with thickness less than 20 nm, which was synthesized at room temperature. We found that the EMI shielding efficiency (EMI SE) of the CuS nanosheet exceeds that of the traditional Cu film in the nanoscale thickness, which is due to high conductivity and the presence of internal dipole structures of the CuS nanosheet that contribute to absorption due to the damping of dipole oscillation. In addition, the CuS nanosheet exhibited high mechanical stability (104 cycles at 3 mm bending radius) and air stability (25 °C, 1 atm), which far exceeded the performance of the Cu nanosheet film. This remarkable performance of nanometer-thick CuS proposes an important pathway toward designing EMI shielding materials for wearable, flexible, and next-generation electronic applications.

Facile fabrication of MXene/cellulose fiber composite film with homogeneous and aligned structure via wet co-milling for enhancing electromagnetic interference shielding performance

MXene/cellulose nanofiber (MXene/CNF) composites have demonstrated promising performance in various areas. Here, we propose a one-pot wet co-milling strategy to produce homogeneous delaminated-MXene nanosheets/micro-fibrillated cellulose fibers slurry from multilayer-MXene particles/raw cellulose fibrils mixture on a large scale. The vacuum-filtrated MXene/CNF composite films can be fabricated from the well-dispersed slurry with a homogeneous and aligned structure which is convincingly demonstrated through laser scanning confocal microscopy (LSCM) and small-angle X-ray scattering (SAXS). Owning to the well-refined structure, the mechanical properties, conductivity, and electromagnetic interference (EMI) shielding performance of MXene/CNF composite films exhibit significant enhancement with 13882.8%, 3725.5%, and 63.5%, respectively. More importantly, the excellent EMI shielding performance of MXene/CNF composite films reaches up to 36.51 dB at a thickness of 20 μm. This wet co-milling strategy demonstrates potential in the facile manufacture of high-performance MXene-based composite materials for flexible EMI shielding materials.

Constructing hierarchical structure via in situ growth of CNT in SiO2-coated carbon foam for high-performance EMI shielding application

Carbonated melamine foam (CMF) with a three-dimensional (3D) inner connected network is considered as one of the promising candidates to fabricate electromagnetic interference (EMI) shielding materials. To further improve EMI shielding performance, CMF based hybrids with three-dimensional structure by the combination of SiO2 and in-situ growth carbon nanotubes (CNT) have been synthesized for preparing polydimethylsiloxane (PDMS) composite: CMF@SiO2-CNT/PDMS. Owing to the structural match between the length of CNT and the diameter of holes in the CMF@SiO2, the relatively high electrical conductivity of 50.43 S/m has been achieved in the composite with the thickness of 2 mm, which assures an excellent EMI shielding effectiveness (SET = 61.34 dB) in the frequency range from 8.2 to 12.4 GHz. Meanwhile, a high absorption effectiveness (SEA = 53.65 dB) of the composite infers an absorption dominant performance of the composite because of the unique porous structure and inter-connected conductive network, which helps to avoid secondary EMI pollution. We hope this work can provide a new route for fabricating EMI shielding materials with high performance.

3D Microstructured Frequency Selective Surface Based on Carbonized Polyimide Films for Terahertz Applications

AbstractIn recent years, frequency selective surface (FSS)‐based two‐dimensional (2D) and three‐dimensional (3D) carbon materials such as carbon nanofibers, carbon nanotubes, and carbon‐filled filaments are essential tools to design millimeter‐wave radomes, absorbers, electromagnetic interference (EMI) shielding, and antenna reflectors in gigahertz (GHz) regimes. Terahertz (THz) technologies are gaining attentions from medical imaging to security surveillance. In this work, a 3D microstructured FSS using carbon‐based polyimide as a precursor to enhance the resonant frequency at the THz range. Furthermore, gold nanoparticles (AuNPs) are embedded on 3D microsturctured carbonized polyimide (3D‐CPI) film to improve their FSS property through plasmonic effects. From the time domain spectroscopy measurements, 3D‐CPI FSS film shows band‐stop filter properties in the frequency range of 0.5–1.5 THz and with a maximum return loss (RL) of 40.5 dB (at the resonant frequency of 1 THz). The 3D‐CPI/AuNPs film demonstrates the highest RL of 43.7 dB at the higher excitation resonance frequency ≈1.06 THz due to the interaction of plasmonic electrons with scattered delocalized electrons in carbon, which induces the mechanisms for EMI shielding. The results will open insight into 3D plasmonic carbon microstructures as an EMI shielding material at THz frequency.

Electromagnetic shielding of Optically-Transparent and Electrically-Insulating ionic solutions

High-tech electronic and communication devices require advanced materials for their protection against electromagnetic interference (EMI). Electrically conductive solid materials, such as metals, are typically employed as EMI shields owing to their high shielding performance caused by their high electronic conductivity. Herein, electrically insulative and ionically conducting aqueous ionic solutions of KBr, NaCl, and CaCl2 salts are investigated with a focus on their effective EMI shielding performance, which is mechanistically different from that of conventional solid materials. A 5m KBr solution exhibits an optimal EMI shielding effectiveness of 61.3 dB at 5-mm thickness. Debye and Drude theoretical models, which describe polarization of dipolar water molecules and ionic conduction of mobile ions, respectively, are invoked to elucidate the absorption-dominant EMI shielding mechanism of the optically transparent aqueous ionic solutions in X-band (8.2–12.4 GHz) frequency range. Cost-effective aqueous ionic solutions can be used as efficient and lightweight EMI shielding materials providing strong optical transparency in advanced electronic systems.

Evaluation, fabrication and dynamic performance regulation of green EMI-shielding materials with low reflectivity: A review

Electromagnetic interference (EMI) shielding materials have been employed to diminish environmental electromagnetic radiations by reflecting and absorbing transmitted EM wave. However, most of the researchers focus on improving the electrical conductivity of the materials, which is conducive to improving EMI shielding performance, but it will also increase the EM reflection, leading to the inevitable secondary EM pollution. Therefore, it is momentous to develop novel green EMI shielding materials with low reflectivity for environmentally friendly applications. In this review, we introduce the evaluation methods and influence factors of low-reflectivity green EMI shielding materials. Subsequently, the recently reported fabrication approaches as well as the corresponding EMI shielding performance and mechanism in regards to the low-reflectivity green EMI shields are summarized, and the ways for dynamic performance regulation of recently reported EMI shielding materials are concluded as well. Finally, the extant challenges of design and fabrication for low-reflectivity EMI shielding materials needed to be concerned are proposed, and the research tendency of low-reflectivity EMI shielding materials are prospected.

Wrinkled Titanium Carbide (MXene) with Surface Charge Polarizations through Chemical Etching for Superior Electromagnetic Interference Shielding

AbstractDespite the fact that the high conductivity of two‐dimensional laminated transition metal carbides/nitrides (MXenes) contributes to the outstanding electromagnetic interference (EMI) shielding by the reflection of electromagnetic waves (EWs), it is difficulty to improve EMI shielding by pursuing higher conductivity due to the limitation of intrinsic properties. Here, we achieve superior EMI shielding by introducing the absorption of EWs in MXenes with micro‐sized wrinkles which are induced by abundant Ti vacancies under chemical etching. The shielding effectiveness is up to 107 dB at a thickness of 20 μm. Combining with atomic‐scale structure observation and the first‐principles calculations, it is concluded that the promotion of EMI shielding originates from the resonant absorption of formed electric dipoles induced by the asymmetrical distribution of charge densities near Ti vacancies. Our results could open a new vista for developing two‐dimensional EMI shielding materials.

Wrinkled Titanium Carbide (MXene) with Surface Charge Polarizations through Chemical Etching for Superior Electromagnetic Interference Shielding.

Despite the fact that the high conductivity of two-dimensional laminated transition metal carbides/nitrides (MXenes) contributes to the outstanding electromagnetic interference (EMI) shielding by the reflection of electromagnetic waves (EWs), it is difficulty to improve EMI shielding by pursuing higher conductivity due to the limitation of intrinsic properties. Here, we achieve superior EMI shielding by introducing the absorption of EWs in MXenes with micro-sized wrinkles which are induced by abundant Ti vacancies under chemical etching. The shielding effectiveness is up to 107 dB at a thickness of 20 μm. Combining with atomic-scale structure observation and the first-principles calculations, it is concluded that the promotion of EMI shielding originates from the resonant absorption of formed electric dipoles induced by the asymmetrical distribution of charge densities near Ti vacancies. Our results could open a new vista for developing two-dimensional EMI shielding materials.

Flexible and mechanically strong MXene/FeCo@C decorated carbon cloth: A multifunctional electromagnetic interference shielding material

High-performance electromagnetic interference (EMI) shielding materials are urgently demanded to address worrisome electromagnetic radiation pollution. Nowadays, the increasingly complex application environments have put forward higher requirements for EMI shielding materials. However, it is still a challenge to simultaneously achieve the flexibility, high mechanical strength and multiple functions of EMI shielding materials via a facile manufacturing strategy. Herein, the flexible and mechanically strong MXene/FeCo alloy@carbon decorated carbon cloth (CC-FCM) with excellent EMI shielding, Joule heating, and pressure sensing performances is fabricated by a facile and scalable approach. The introduction of polydimethylsiloxane (PDMS) layer can endow the cloth with better durability and higher tensile strength (403.2 MPa). The EMI shielding effectiveness of CC-FCM/PDMS composites can reach 45.5 dB for one piece and even up to 80.5 dB for three pieces, which can maintain high retention of more than 90% after mechanical deformation, corrosion or abrasion. In addition, the CC-FCM/PDMS composite possesses outstanding low-voltage driven Joule heating ability, and the multilayered CC-FCM also exhibits satisfactory pressure sensing performance for human motion monitoring. These excellent comprehensive performances endow the CC-FCM with great potential for applications in aerospace, portable equipment and wearable smart electronics.

Mechanically and environmentally robust composite nanofibers with embedded MXene for wearable shielding of electromagnetic wave

Flexible materials based on two-dimensional titanium carbides (MXene) exhibit great potential for electromagnetic interference (EMI) shielding applications. However, MXene base EMI shielding materials usually cannot possess combined favorable properties of high strength, environmental stability and air permeability, which can inhibit practical implementations as wearable components. Herein, newly designed EMI shielding Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) composite fabric with MXene embedded in nanofibers have been prepared by one-step electrospinning technique. The highly hydrophobic composite fabric shows excellent specific EMI shielding effectiveness of 160 dB/mm, which remains unchanged when exposed in acidic, alkali or saline solutions for 10 days due to the polymer matrix protection. Moreover, the embedded MXene can greatly enhance the strength and modulus of the fabric. The ultimate strength of the highly flexible composite can reach as high as20 MPa, which is 33% higher compared with untreated PVDF-HFP fabric. Our study could allow us to implement MXene based EMI shielding materials for more practical applications.

Fe3O4@PA6/MWCNT composites with multiple gradient segregated structures for electromagnetic shielding with low reflection

AbstractGreen electromagnetic interference (EMI) shielding materials have been popularly accepted as the most promising EMI shielding material used in the electronic industrial community. Nevertheless, the design and optimization for both material and structure to achieve this function remain many challenges. Herein, Fe3O4@PA6 microspheres were fabricated by an unusual reaction‐induced phase separation method, where Fe3O4 nanoparticles were in situ introduced into the polymerization system. Interestingly, most Fe3O4 nanoparticles spontaneously immigrated into PA6 microsphere, forming Fe3O4@PA6 composite microspheres, and more interestingly, the saturation magnetization and particle size of the microspheres are highly associated. Therefore, the microspheres with specific particle size and magnetic property were easily obtained by simple sieving. These microspheres were then coated by MWCNT and hot‐compressed into EMI materials with segregated structures. A multilayered structure with positive conductivity gradients and negative magnetic gradients were created. Due to this structure, electromagnetic wave can enter the materials from the impedance matching channel without a large amount of reflection on the surface. The results show that with the increase in the number of composite layers, the EMI SE increases to 24.8 dB, and the R‐value is significantly reduced to 0.51. This work provides a new feasible idea for designing low‐reflection EMI composites.

Quantitative Interpretation of Electromagnetic Interference Shielding Efficiency: Is It Really a Wave Absorber or a Reflector?

As electromagnetic (EM) pollution continues to increase, electromagnetic interference (EMI) shielding materials have been intensively evaluated in terms of two main shielding mechanisms of reflection and absorption. Since the shielding effectiveness (SE) is represented in the logarithmic scale and in a coupled way of transmission (SET), absorption (SEA), and reflection (SER), often there is a misinterpretation that the EM wave reflectors are regarded as EM wave-absorbing materials. Surprisingly, we found that many materials reported as an EM wave absorber in the literature provide, in fact, less than 50% of EM wave-absorbing capability, i.e., over 50% of EM wave-reflecting feature. According to the theory and definition of EMI SE, the absorption-dominant EMI shielding materials should have the ratio of absorption to incident energy (A) as A > 0.5, which corresponds to a necessary condition that SER < 3.01 dB. The SER subsequently gives SEA in relation to SET. Using this criterion, we classified the EMI shielding materials with their shielding mechanism. The proposed methodology provides significant insight into the evaluation and development of EMI shielding materials.