Flexible Electromagnetic Shielding Research Articles

Electromagnetic shielding Janus membrane for direct current‐type pressure and sliding sensing

AbstractFacing increasing electromagnetic radiation pollution, soft sensors with electromagnetic interference (EMI) shielding is highly desirable. Here, flexible electromagnetic shielding [polyacrylonitrile/Fe3O4/polyaniline]//[multiwalled carbon nanotube/polyvinyl pyrrolidone] (denoted [PAN/Fe3O4/PANI]//[MWCNT/PVP]) Janus membrane is reported for pressure and sliding sensing. The [PAN/Fe3O4/PANI] layer of Janus membrane as the force and sliding sensing unit can generate direct current‐type (DC‐type) voltage signals by conducting polymer/metal Schottky junction, whereas [MWCNT/PVP] layer serves as main electromagnetic shielding unit. Under the vertical force and horizontal sliding of aluminum (Al) foil, it can output DC‐type voltage signals based on the Schottky contact. The performance of [PAN/Fe3O4/PANI]//[MWCNT/PVP] Janus membrane for pressure and sliding sensing is appropriately explored and assessed. Moreover, the Janus membrane exhibits excellent shielding effects with average EMI shielding effectiveness (SE) of 37.54 dB in 8.2–12.4 GHz (X‐Band) frequency ranges. Thus, based on the asymmetrical double‐layer structure, soft DC‐type sensor with EMI shielding is achieved, showing utilization potential in wearable electronics and intelligent robots.

Fabrication and investigation of graphene‐loaded triiron tetraoxide/silicone‐rubber electromagnetic shielding composites based on static magnetic‐field–induced orientation

AbstractGraphene‐loaded triiron tetraoxide/silicone‐rubber composites containing highly loaded graphene‐loaded Fe3O4 (Fe3O4@RGO) particles were fabricated using static magnetic field‐induced alignment. The Fe3O4@RGO particles were characterized through Fourier transform infrared, x‐ray diffraction, SEM, and XPS analyses. Subsequently, the influence of added material and the strength of the magnetic field on the alignment distribution of the filler were examined through a synergistic combination of SEM and Raman spectroscopy. The electrical conductivity and electromagnetic shielding properties of the composites were assessed. The electrical conductivity of the composites increased with increasing filler addition, the 25 wt% filler mixture had the fastest curing rate and the maximum torque, and the continued increase in filler addition led to the occurrence of many defects. Concurrently, the alignment distribution of the filler progressively enhances with the augmentation of magnetic field strength. The composites synthesized at 180 mT exhibit the most substantial alignment, facilitating the establishment of effective conductive pathways. This results in a notable enhancement in electromagnetic shielding effectiveness, approximately 400% greater than that of pure silicone rubber and around 40% higher than that of non‐aligned composites. This approach introduces a novel concept for shaping the structural design of flexible electromagnetic shielding materials.Highlights Highly loaded Fe3O4@RGO was prepared by self‐assembly. The continuous phase structure of Fe3O4@RGO oriented was assessed. Fully oriented Fe3O4@RGO promotes the formation of conductive pathways. Fully oriented Fe3O4@RGO reduced the SER by 13% and increased the SEA by 67%.

Preparation and properties of flexible electromagnetic shielding composites

Preparation and properties of flexible electromagnetic shielding composites

Cobalt‐Based Metallic Glass Microfibers for Flexible Electromagnetic Shielding and Soft Magnetic Properties

AbstractThin and flexible materials that can provide efficient electromagnetic interference (EMI) shielding are urgently needed, particularly those that can be rapidly processed and withstand harsh environments. Cobalt‐based metallic glasses stand out as prime candidates due to their excellent soft magnetic properties, satisfactory shielding features, and mechanical properties. Herein, a recently developed technique is used to fabricate metallic glass microfibers from Co66Fe4Mo2Si16B12 alloy. The produced microfibers are characterized for their size and uniformity by scanning electron microscopy and their amorphous structure is confirmed by X‐ray diffraction (XRD) and differential scanning calorimetry (DSC). The cobalt‐based metallic glass microfibers show an EMI shielding factor that reaches five in the static regime and obtains an up to 25‐fold increase of the attenuation constant in the Ku frequency band. This performance originates from the combination of soft magnetic properties and excellent electrical conductivity. In addition, the flexible microfibers exhibit excellent hardness and elasticity making them suitable for EMI shielding of complex geometries. Their hardness and elastic modulus are measured by nanoindentation to be 11.31 ± 0.60 GPa, and 110.54 ± 11.24 GPa, respectively.

Fabrication of Flexible FCI/PDMS Electromagnetic Shielding Composites Based on Pulsed Magnetic Field-Induced Alignment

Conductive polymer composites have been utilized in the field of electromagnetic interference (EMI) shielding, albeit requiring a high concentration of conductive fillers to achieve desirable EMI performance. To address this issue and enable the creation of superior EMI shielding composites with reduced filler loadings, this study employed a pulsed magnetic field featuring an amplitude of 0.7 T, a pulse width of 10 μs, and a frequency of 100 Hz to align flaky carbonyl iron (FCI) in poly(dimethylsiloxane) (PDMS). This method resulted in an improved EMI shielding performance of the composites. The outcomes revealed that the pulsed magnetic field effectively controlled the orientation of the FCI, forming a conductive network structure, with the average orientation angle of the FCI reaching 69.3°. The aligned composites exhibited a significant improvement in EMI shielding effectiveness, with the enhancement effect reaching 37.53% and the EMI shielding effectiveness reaching 24.87 dB. Moreover, the flexible tensile properties of the aligned composites were superior to those of the unaligned composites, particularly the elongation at break, which reached 197.46%. The concordance between the theoretical analysis and experimental results affirms the efficacy of the microsecond pulsed magnetic field in enhancing the EMI shielding performance of composite materials. Ultimately, the high-performance, flexible electromagnetic shielding composite materials prepared in this study demonstrate potential for use in advanced electronic equipment.

Flexible Electromagnetic Shielding Nano-Composites Based on Silicon and NiFe2O4 Powders.

In this paper, the obtaining and characterization of five experimental models of novel polymer composite materials with ferrite nano-powder are presented. The composites were obtained by mechanically mixing two components and pressing the obtained mixture on a hot plate press. The ferrite powders were obtained by an innovative economic co-precipitation route. The characterization of these composites consisted of physical and thermal properties: hydrostatic density, scanning electron microscopy (SEM), and TG DSC thermal analyses, along with functional electromagnetic tests in order to demonstrate the functionality of these materials as electromagnetic shields (magnetic permeability, dielectric characteristics, and shielding effectiveness). The purpose of this work was to obtain a flexible composite material, applicable to any type of architecture for the electrical and automotive industry, necessary for protection against electromagnetic interference. The results demonstrated the efficiency of such materials at lower frequencies, but also in the microwave domain, with higher thermal stability and lifetime.

Flexible, Stretchable, and Thin Films Based on Functionalized Carbon Nanofiber/Graphene Nanostructures for Electromagnetic Interference Shielding

Flexible electromagnetic shielding materials (ESMs) are becoming progressively important to flexible and conformal electronic devices operating in civil, aerospace, and military industries. There is a legitimate need to fabricate flexible, thin, featherweight, and stretchable materials with higher electromagnetic interference shielding effectiveness (EMI SE) that can handle harsh environments. Graphene nanoplatelets (GNPs) are synthesized by microwave-supported exfoliation of graphite proceeded by water-bath sonication, whereas functionalized carbon nanofibers (FCNFs) are synthesized via acid functionalization using HNO3. The effects of conventional CNF, FCNF, and GNP are observed by embedding in the polyurethane (PU) matrix to obtain flexible, highly stretchable (>400%), lightweight, and thin (300 μm) nanocomposites for enhanced EMI shielding performance. The GFCNF/PU nanocomposite showed uniform distribution and excellent microwave properties at low weight%. An improvement in the total EMI SE (SET) value is noticed by adding GNP (2, 4, and 6 wt %) in FCNF4, and a maximum SET value of 60.55 dB is obtained for FCNF/GNP (4/6 wt %). A negligible change in the value of EMI SE is observed after 500 mechanical bending cycles and bath-sonicating the nanocomposites in distilled water, confirming the efficiency of operating in the complex environmental condition. Further, the value of SET is measured by placing the nanocomposites at different bending radii inside the waveguide to verify the practical applicability of fabricated nanocomposites in conformal devices. EMI shielding is also calculated for nanocomposites through simulation in the CST microwave studio tool (in the X-band), further extending the analysis for broadband frequency (1–18 GHz).

Flexible bilayer Ti3C2Tx MXene/cellulose nanocrystals/waterborne polyurethane composite film with excellent mechanical properties for electromagnetic interference shielding

To address electromagnetic wave (EMW) pollution, the development of ultrathin and flexible electromagnetic shielding materials is essential. High electromagnetic interference (EMI) shielding performance while retaining robust mechanical properties remains a challenging hurdle. In this work, bilayer structured MXene/CNC/WPU (MCW-X) composite films were fabricated via alternating filtration assisted by vacuum. On the one hand, a conductive network is formed between CNC and MXene nanosheets, which enhances the electrical conductivity of the composite film as well as the stable water-oxidation stability. On the other hand, the interaction between WPU and MXene nanosheets increases the sliding between the layers of MXene nanosheets, hence enhancing the tensile strength and toughness. Meanwhile, the incorporation of CNC and WPU into MXene nanosheets increases the interlayer spaces of the composite films, optimizes impedance matching, and boosts the EMI shielding performance. MCW-4.5 sample composite (CNC 20 wt%) exhibits excellent electrical conductivity of 606.1 S/cm, resulting in a high-performance EMI shielding of 54.2 dB in X-band with a thickness of 35 µm. Meanwhile, it exhibits exceptional mechanical properties (elastic modulus of 3652.70 MPa, tensile strength of 52.2 MPa). Consequently, MCW-X composite films have a significant utilization potential in the field of green, ultrathin, and flexible EMI shielding.

Ultrathin and Flexible ANF/APP/PRGO Composite Films for High-Performance Electromagnetic Interference Shielding and Joule Heating

With the problem of electromagnetic interference (EMI) increasingly serious, the development of lightweight and flexible electromagnetic shielding composite films with excellent Joule heating performance and good mechanical properties is of great significance for modern electronic devices. In this study, we prepared aramid nanofiber/aramid nanofiber-poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/polydopamine-modified reduced graphene oxide (ANF/APP/PRGO) composite films with excellent electromagnetic shielding properties and electrical heating properties by stepwise vacuum filtration. With high conductivity (124.10 S/cm) and multi-interface electromagnetic wave reflection caused by the layered structure, the composite films achieve an EMI shielding effectiveness (SE) as high as 40.52 dB at 8.2–12.4 GHz (X-band) with a low thickness (∼22 μm). At the same time, the composite films also exhibit excellent electrical heating performance with fast response and cycle stability, which can reach a surface saturation temperature as high as 127.6 °C under an applied voltage of 7 V. Therefore, it can be envisaged that the ANF/APP/PRGO composite films have certain practical application value in the fields of electromagnetic shielding and electric heating.

Direct-spun CNT textiles for high-performance electromagnetic interference shielding in an ultra-wide bandwidth

Electromagnetic interference (EMI) generated by electronic devices is disruptive to surrounding electronic components and deemed harmful to human beings. As high-speed, miniaturized mobile devices become ubiquitous, developing lightweight, thin, and flexible electromagnetic shielding materials (ESMs) to replace the common metallic ones is of utmost importance. Here we report the development of a high-efficiency standalone ESM made of a self-standing CNT mat (CNTM). This textile is electrically conductive (∼50 × 103 S m−1) and can be post-treated by chemical oxidation or thin copper metalization, increasing the conductivity by ∼10 and ∼1000 times, respectively. CNTMs were tested for shielding effectiveness (SE) in an ultra-wide bandwidth of 30 kHz–70 GHz. Maximal SE of >120 dB was measured for a 30 g m−2 CNTM (<100 μm thickness) at 70 GHz. SE normalized by thickness (SE/t) reached a value of >20,000 dB cm−1 for an HCl-oxidized CNTM. Both SE values are the highest values for non-metal-based ESMs. The CNTMs' experimental EMI shielding behavior corresponds to Schelkunoff's theory which confirms that the CNTM SE is dominated by conductivity-dependent reflection at lower frequencies (<1 GHz) and thickness-dependent absorption at higher frequencies. CNTMs (20 g m−2) were utilized as EMI gaskets and in composite EMI enclosures, tested at 10–50 GHz and 50 MHz-90 GHz, respectively. EMI CNT gaskets reached an SE of 120.9 dB at 50 GHz, surpassing the performance of high-end commercial gaskets (600 g m−2). EMI composite boxes laminated with CNTMs reached an SE of 119.9 dB at 90 GHz, outperforming the non-CNT laminated reference.

Metal–organic framework‐derived high‐performance polypyrrole/Ni‐CAT/PI fiber paper‐based electromagnetic shielding composites for high‐frequency electromagnetic wave absorption

AbstractLight‐weight, portability and miniaturization are important characteristics for the next generation of high‐performance electromagnetic interference (EMI) shielding equipment. To meet the current demand for high‐performance EMI shielding materials, this paper proposes a simple and reliable method for preparing multilayer paper‐based composites. Paper‐based composites exhibit light weight, flexibility, easy processing and high temperature resistance. A conductive metal–organic skeleton (Ni‐CAT) layer and polypyrrole (PPy) layer were deposited on a polyimide (PI) fiber surface with an in situ synthesis and gas aggregation method to prepare paper‐based electromagnetic shielding composites with good properties. The results showed that the electromagnetic shielding effect (SE) of the paper‐based composites reached 41.0 dB. After the paper‐based composites underwent multiple ultrasonic washing and bending tests, their electrical conductivity retention rate was as high as 90%. Furthermore, the introduction of PPy/Ni‐CAT enhanced the bonding strength of the PI fibers, which caused the tensile strength of the paper‐based composites to reach 22.3 MPa. Due to the good thermal stability of the composites, they can withstand an open flame and protect the equipment during a fire. Thus, these paper‐based EMI shielding composites hold great promise for flexible electromagnetic shielding materials, protection of smart wearable devices and other fields.

Multifunctional AgNWs@MXene/AgNFs electromagnetic shielding composites for flexible and highly integrated advanced electronics

The electromagnetic interference and heat accumulation pose a significant challenge for the traditional high-density single-function electromagnetic shielding materials in advanced flexible integrated electronics. Herein, nano-silver flakes (AgNFs, reflective layer), MXene (Ti3CNTx, loss layer) and silver nanowires (AgNWs, heat conduction and shielding layer) constructed ordered multi heterogeneous layers high-performance flexible electromagnetic shielding functional composites (AMA composites). Especially the composites exhibited outstanding electromagnetic interference shielding efficiency (EMI SE) of 70.96 dB even with an extremely thin coating of 25 g/m2, which is 350% higher than that of the commercial standard (20 dB). It is worth noting that the AMA composites also possessed certain qualities such as superior thermal conductivity, flame retardancy, chemical resistance, high-temperature resistance (25 °C–100 °C), and mechanical properties (tensile strength of 44.4 MPa, Young's modulus of 0.6 GPa). The composites display application possibilities in highly integrated advanced flexible electronic products and wearable electronic devices, as well as provide structural design and research ideas for the usage of a new MXene material (Ti3CNTx) in electromagnetic shielding composite materials.

Fabrication of effective electromagnetic shielding leather with a chromium-free multi-network structure

Chrome-free tanning and intelligentization are hot topics in leather-related research. In this work, green chrome-free tanned electromagnetic shielding leather is proposed based on the modification of skin collagen fibers using polyionic liquids (PILs), metal-organic framework-layered double hydroxide (MOF-LDH), and polyaniline (PANI). First, a network-interspersed PILs/MOF-LDH-Zr structure was synthesized using MOF-LDH, ionic liquid, methacrylic acid, and zirconium sulfate as raw materials based on a radical polymerization approach. Then, PANI was grown in situ on the surface of the leather to help construct a green chrome-free tanned electromagnetic shielding leather with a leather shrinkage temperature of 94.5 °C and an effective EMI shielding capability of 32.3 dB. The enhanced tanning performance of PILs/MOF-LDH-Zr may be due to the multi-point cross-linking of –COOH, imidazole groups, and metallic zirconium. The conductive properties of PANI and the porous network structure of leather are helpful to realize electromagnetic shielding of the leather. Interestingly, after 1000 bending tests, more than 99% of the shielding effectiveness (SE) could be retained. As such, an effective and powerful strategy is proposed to construct flexible electromagnetic shielding material based on an eco-friendly chrome-free tanning approach.

Highly conductive and flexible electromagnetic shielding film obtained by molding an expanded graphite/silver/sodium alginate aerogel

The development of flexible, thin and excellent electromagnetic interference (EMI) shielding performance polymer-based materials is a powerful means to solve electromagnetic pollution. However, traditional methods for preparing light and thin materials, such as vacuum-assisted filtration and pouring molding method, still have shortcomings. Here, we innovatively developed a green, sustainable, large-scale “sol-gel-compression” film-forming technology and obtained flexible EG/AgNPs/SA composite film with a thickness of only 0.16 mm, high electrical conductivity (12,600 S/m), and supreme electromagnetic interference (EMI) shielding efficiency (40.1 dB). The preparation technology is simple to operate, and at the same time, the molding effect effectively promotes the formation of the conductive network and takes into account the thickness and flexibility of the material. Owing to the ultrahigh conductivity, superior EMI shielding efficiency, and flexibility, the EG/AgNPs/SA composite films present significant advantages over other carbon-polymer materials and demonstrate considerable application potential in electromagnetic protection fields such as the communications industry, artificial intelligence, and wearable electronics.

EMI shielding of cobalt, red onion husk biochar and carbon short fiber‐PVA composite on X and Ku band frequencies

AbstractThis present study discusses the effects of doped novel cobalt‐onion peel‐based water soluble Poly vinyl alcohol (PVA) composite for its electromagnetic interference shielding (EMI) effectiveness in high‐frequency bands such as X and Ku region. The primary aim of this study was to prepare a flexible electromagnetic shielding material for protecting electronic gadgets from the EMI effect. The biochar particles were prepared from red onion peel and mixed with cobalt/chopped carbon fiber (CCF) to form a compound structure. According to the results, the biochar and CCF addition improved the relative permittivity up to 9.6. Similarly, the hysteresis analysis showed a broad “S” curve for 2 vol% cobalt‐added PVA composite. Moreover the doped composites are better in mechanical properties and the highest tensile strength of 79 MPa with Shore‐D hardness of 37 was noted for PV3 composite designation. Finally, the highest wave shielding of −44.37 dB and − 49.62 dB for X and Ku band were observed for composite designation PVA4. This EMI shielding effectiveness improved composites could be used as shielding material for modern industrial, defense, and medical applications.

Ferromagnetic-assisted Maxwell’s displacement current based on iron/polymer composite for improving the triboelectric nanogenerator output

Triboelectric nanogenerator (TENG) based on Maxwell’s displacement current as the driving force has broad applications in energy harvesting and self-powered sensors. However, the effect of doped ferromagnetic materials with bearing an external magnetic field on TENG’s displacement current has not been clearly revealed. Herein, a ferromagnetic-assisted Maxwell’s displacement current is proposed for improving TENG output based on polymer/iron composite film (PICF). Based on Maxwell’s equations, the magnetizing current of the ferromagnetic medium coupled with the displacement current is investigated theoretically for boosting TENG output and verified simulationally and experimentally. Comparing TENG output with the magnetization method of PICF, the initial magnetization significantly determines the coupling mechanism between magnetizing current and displacement current. Moreover, the strength and direction of an external magnetic field further reveal the mechanism impacting the initial magnetization on TENG’s displacement current. A short-circuit current density of 27 mA/m2 and instantaneous power density of 2 W/m2 are achieved by the champion TENG, which are 800% and 8200% higher than those of pristine polymer. Finally, a distributed TENG array is developed for efficiently harvesting distributed energy to demonstrate the application potential of the improved TENG in self-powered systems. This work elaborates the coupling mechanism of the magnetizing current with TENG’s displacement current, which provides general guidance for investigating efficient energy harvester toward self-powered sensors, wearable electronics and flexible electromagnetic shielding devices.

Experiment and simulation of flexible CNT/SA/PDMS electromagnetic shielding composite

Flexible electromagnetic shielding composites have a great potential for wide range applications. In this study, two flexible composites were produced by plating Ni nanoparticles on carbon nanotubes (CNTs) or infiltrating carbon nanofibers/polydimethylsiloxane (CNF/PDMS) polymer into CNT/sodium alginate (CNT/SA) sponge skeleton (CNT/SA/CNF/PDMS composites). The composites are tested under the X band in the frequency range of 8.2 – 12.4 GHz, the electromagnetic interference shielding effectiveness (EMI-SE) values of the above two composites are almost as twice as that of CNT/SA/PDMS composite at a same CNT loading. Introducing nano-sized Ni particles on CNT improved the microwave absorption capacity of the composite, while adding CNF on the PDMS matrix enhanced the conductivity of these composites. Under 10% strain, both flexible composites show stable conductivity. Simulation and calculation results shown that increasing the cladding rate of Ni nanoparticles on the surface of CNT, reducing the average size of Ni particles, and increasing the loading of CNF in PDMS matrix can significantly improve conductivity and then EMI performance of the materials. All of these could benefit for the design of flexible electromagnetic shielding composites.

Flexible graphene/silver nanoparticles/aluminum film paper for high-performance electromagnetic interference shielding

Rubber and plastic are widely acted as substrates in flexible electromagnetic shielding (EMS) materials. However, these materials have several drawbacks in practical applications, such as potential environmental concerns and difficulties in degrading. In this work, a biodegradability paper-based material composed of electromagnetic wave loss layer (graphene/ silver nanoparticles (AgNPs) coating) and reflective layer (aluminum film layer) was successfully fabricated. The electromagnetic wave loss layer constructed three-dimensional (3D) electric conductive network to facilitate the timely transfer of electrons and heat energy obtained from electromagnetic waves. Meanwhile, the reflective layer received electrons and heat from the electric conductive network and make a small quantity of transmission wave back to the wave loss layer. The resulting material exhibited an ultrahigh electromagnetic interference shielding effectiveness (EMI SE) of 92.29 dB within 8–13 GHz, electrical conductivity of 4431 S/m, mechanical properties with a tensile strength of 32 MPa and elongation at break of 6.65%. Compared to the traditional EMS materials, the composite material integrated with excellent EMI SE, heat transfer performance, and weatherability, which has potential applications in microelectronics, high integrated circuits, and flexible electronic fields.

Electromagnetic wave absorbing properties of carbon black-filled natural rubber latex

This article investigated the electromagnetic wave absorbing properties of natural rubber latex (NRL) foam filled with carbon black. The influence of different grades (N330, N660 and conductive grade) of carbon black and content on the foam morphology and electromagnetic wave absorption were of interest. The experimental results revealed that the addition of carbon black can improve the ability of electromagnetic wave absorption NRL over a wide frequency range. The NRL foam filled with the conductive carbon black exhibited more electromagnetic wave susceptibility in comparison to the those filled with classical carbon black. The addition of carbon black results in a decrease in cell size and increase in the number of foam cells. The proposed NRL foams are expected to be used as electromagnetic absorber in lightweight and flexible electromagnetic shielding materials.

Study of enhanced dielectric permittivity of functionalize multiwall carbon nanotube-based polyvinylidene fluoride free-standing film for flexible storage device

We report the dielectric properties of flexible polyvinylidene fluoride (PVDF) and multiwall carbon nanotube (MWCNT) composite films prepared by solution casting route. The Fourier Transform Infrared Spectroscopy (FTIR) and Raman study engraved more dipolar phases within the carboxyl functionalize (f-MWCNT) embedded PVDF composite film. The dielectric permittivity enhances but the dielectric loss reduces for f-MWCNT embedded PVDF film compared to pristine MWCNT (p-MWCNT) embedded film. The dipolar interaction between –CF2 groups in PVDF and –COOH groups of CNT plays a crucial role in enhancing the dielectric constant. The resistance-voltage plot engraves the formation of the hysteresis loop of the nanocomposite film. The enhanced dielectric permittivity and appearance of a hysteresis loop in f-MWCNT embedded PVDF film can be utilized as the flexible storage device material. Apart from the above, the low value of skin depth of the film makes it a promising candidate for designing a flexible electromagnetic shielding membrane.