Electromagnetic Shielding Research Articles

Tunable negative permittivity behavior and excellent electromagnetic shielding performance of pyrolytic carbon‐glass fiber felt/epoxy resin metacomposites

AbstractEffective and accurate adjustment of negative permittivity behavior is worthy of further investigation. Herein, pyrolytic carbon‐glass fiber felt/epoxy resin (PyC‐GFF/ER) metacomposites with tunable negative permittivity were prepared using an impregnation‐calcination method. The permittivity, electrical conductivity, and electromagnetic shielding performance of the polymer metacomposites were investigated. Due to the inherent three‐dimensional structural network of GFF, the PyC adhering to the surface of glass fiber easily formed a conductive network in the composites. As the PyC content increased in the ER composites, the conductivity mechanism changed from hopping conduction to metal‐like conduction. The ER composites with high PyC contents showed negative permittivity behavior and the epsilon‐near‐zero response owing to the low frequency plasma state of free electrons in the PyC‐conduction network. By controlling the PyC content, the negative permittivity behavior of ER composites could be effectively tuned. With the increase in PyC content, the values of negative permittivity increased, and the epsilon‐near‐zero frequency shifted to a higher frequency. Moreover, the ER composites with high PyC contents showed excellent electromagnetic shielding properties (29.4 dB) at X‐band. This work not only provided a feasible method to realize the tunable negative permittivity of polymer metacomposites, but also promoted its application in the microwave field.Highlights The pyrolytic carbon‐glass fiber felt/epoxy resin composites were fabricated. The negative permittivity was first reported in the PyC‐GFF/ER composites. Tunable negative permittivity could be well explained by Drude model. The polymer composites had excellent electromagnetic shielding property.

Tunable Negative Permittivity and Magnetic Properties of Ag/BLM Ceramic Metacomposites

Abstract Percolation composites with tunable negative permittivity have garnered significant attention due to their potential use in the field of electromagnetic interference shielding, near field amplification, antennas, and sensors. However, studies on the magnetic property at a frequency range of 100 MHz to 1 GHz are relatively scarce. The objective of this study was to examine the magnetic property and adjustable negative permittivity of silver/La-doped barium ferrite(Ag/BLM) ceramic metacomposites. In this study, Ag/BLM ceramic metacomposites with varying Ag content were prepared using a simple impregnation-calcination method. We investigate the permittivity, reactance, and permeability of Ag/BLM ceramic metacomposites at 100 MHz ~ 1GHz. The findings indicate that the percolation threshold for Ag/BLM ceramic metacomposites with x wt% is between 10 wt% and 19 wt%. When Ag content reaches 19 wt%, it creates a conductive network that generates a high number of free electrons. This leads to low-frequency plasma states and results in negative permittivity. Meanwhile, the permeability of Ag/BLM ceramic metacomposites shows the frequency dispersion due to the magnetic resonance and eddy current. Therefore, this study's findings suggest that composites with tunable negative permittivity and permeability may be developed and utilised for microwave absorption, antenna design, and wireless power transmission.

Shielding Effectiveness of Textile Woven Fabric with Carbon Nanotubes Yarn

ABSTRACT This study explores the electromagnetic properties of flat textile products enhanced with carbon nanotube (CNT) threads used as the weft. CNT threads, fabricated via dry-spinning, were integrated into fabrics by wrapping them around steel threads to form a solenoid-like structure. To further improve electromagnetic attenuation, the CNT yarn was coated with graphene oxide and silver nanoparticles. The research assessed the impact of these modifications on the fabric’s ability to attenuate alternating electromagnetic fields across a range of frequencies. Results showed enhanced attenuation at 30 MHz and 500 MHz. CNT yarn wrapped around steel threads achieved attenuation efficiencies of 18 dB at 30 MHz and 22 dB at 500 MHz, with a notable 10 dB improvement at 30 MHz over the reference. Fabrics with CNT yarn coated with graphene oxide demonstrated similar performance to the reference fabric at 500 MHz and an 8 dB increase at 30 MHz. Similarly, CNT yarn with silver nanoparticles showed comparable performance at higher frequencies but matched the reference at 30 MHz. These results indicate significant enhancement at lower frequencies, with benefits diminishing at higher. This study underscores the potential of integrating CNTs and metal nanoparticles into textiles to improve electromagnetic shielding, especially across specific frequencies.

Analysis of Shielding Performance in Double-Layered Enclosures with Integrated Absorbers

Generally, various technologies, including waveguide below cutoff (WBC), gasket sealing, and bonding, are employed in metallic enclosures to achieve the high electromagnetic shielding performance required for EMP protection and EMC countermeasures in shielding structures or facilities. While the shielding structure or facility is properly constructed and maintained according to design specifications, its electromagnetic shielding performance can remain at the required level, effectively protecting internal electrical and electronic equipment from external electromagnetic interference. However, unintended apertures often occur during the construction or maintenance of shielding facilities, compromising their shielding performance. Therefore, it is crucial to develop technologies that prevent shielding effectiveness degradation caused by both intentional and unintentional apertures. This paper proposes a structure incorporating a composite absorber (made of dielectric and magnetic absorber) within a double metal panel of enclosure featuring an aperture, aimed at maintaining and improving the facility’s shielding performance. The effectiveness of the proposed structure was validated through numerical simulation.

Flexible Thermoelectric BiSbTe/Carbon Paper/BiSbTe Sandwiches for Bimode Temperature‐Pressure Sensors

AbstractBimode temperature‐pressure sensors hold significant promise in personal health monitoring, wearables and robotic signal detection. Traditional bimode sensors typically combine two independent sensors, leading to fabrication complexity. This study develops a bimode temperature‐pressure sensor by using a facile electrodeposition method to create sandwiched BiSbTe/Carbon Paper/BiSbTe thin films and stacking them to a vertical structure. It demonstrates high sensitivity for temperature sensing, capable of detecting temperature difference as low as 1 K, and a rapid response time of 0.92 s due to a vertical structure. Utilizing its thermoelectric mechanism, the sensor achieves self‐powered sensing for finger touch and respiration states. Furthermore, its island‐like contact surface ensures high sensitivity with an extremely fast response time of 0.17 s, by rapidly changing contact resistance under pressure, allowing it to detect various human behaviors, including body movements and micro‐expressions. Beyond its sensing capabilities, the film excels in flexibility, electromagnetic interference shielding, and stability, presenting significant potential for integration into self‐powered electronic skin systems for health monitoring, wearables, artificial intelligence, and other electronic skin applications.

Analysis and Design of a Recyclable Inductive Power Transfer System for Sustainable Multi-Stage Rocket Microgrid with Multi-Constant Voltage Output Characteristics—Theoretical Considerations

After a traditional one-time rocket is launched, most of its parts will fall into the atmosphere and burn or fall into the ocean. The parts cannot be recycled, so the cost is relatively high. Multi-stage rockets can be recovered after launch, which greatly reduces the cost of space launches. Moreover, recycling rockets can reduce the generation of waste and reduce pollution and damage to the environment. With the reduction in rocket launch costs and technological advances, space exploration and development can be carried out more frequently and economically. It provides technical support for the sustainable use of space resources. It not only promotes the sustainable development of the aerospace field but also has a positive impact on global environmental protection, resource utilization, and economic development. In order to adapt to the stage-by-stage separation structure of the rocket, this paper proposes a new multi-stage rocket inductive power transfer (IPT) system to power the rocket microgrid. The planar coil structure is used to form wireless power transfer between each stage of the rocket, reducing the volume of the magnetic coupling structure. The volume of the circuit topology structure is reduced by introducing an auxiliary coil. An equivalent three-stage S/T topology is proposed, and the constant voltage output characteristics of multiple loads are analyzed. A multi-stage coil structure is proposed to supply power to multiple loads simultaneously. In order to eliminate undesired magnetic coupling between coils, ferrite cores are added between coils for effective electromagnetic shielding. The parameters of the magnetic coupling structure are optimized based on the finite element method (FEM). A prototype of the proposed IPT system is built to simulate a multi-stage rocket. A series of experiments are conducted to verify the advantages of the proposed IPT system, and the three-stage rocket system efficiency reached 88.5%. This project is theoretical. Its verification was performed only in the laboratory conditions.

Ultra-high strength and flame retardant carbon aerogel composites with efficient electromagnetic interference shielding and superior thermal insulation via nano-repairing route

Carbon aerogel composites (CAs) have received numerous attention for protection of aircraft due to their unique properties. However, the shrinkage mismatch between rigid fibers and carbon sources during carbonization dramatically weakens the performance of CAs, and no significant breakthroughs have been made. We propose a vacuum impregnation assisted nano-repairing (VINR) strategy to fabricate crack-free carbon fiber reinforced carbon aerogel (Cf/CA) composites with high strength, electromagnetic interference shielding and thermal insulation. The cross-confined, overlapping nano-CA particles greatly limits the shrinkage of the carbon source, conferring excellent mechanical properties to Cf/CA, and its compressive strength and modulus reaches 3.93 MPa and 69.96 MPa in XY direction and 2.03 MPa and 40.67 MPa in Z direction, respectively, at 5% strain. In addition, Cf/CA exhibits significant thermal insulation (0.054 W/(m·K) at 25 °C under air condition) and superior electromagnetic interference shielding properties (EMI SE is ∼48.52 dB at a thickness of ∼2 mm). Herein, the structurally optimized Cf/CA provides a promising solution for multi-effect protection for critical electronic devices of aircraft in special service environments.

The enhancement in microstructure, optical and electromagnetic shielding properties of Al-doped Ag thin films by annealing treatment

Ag thin films having attractive optical transmittance and effective shielding capability are usually used as a preferred choice for the transparent electromagnetic shielding windows. Whereas, the Ag films are grown primarily via an island growth (Volmer-Weber) mechanism, which greatly restricts its application. In this study, by introducing Al atoms and suitable annealing treatment, the continuous and smooth Ag thin films are successfully fabricated by magnetron co-sputtering method. The effect of annealing temperature on the microstructure, optical and electromagnetic shielding properties of the films are conducted the comprehensive and profound study. Our results indicate that the 5 mol% Al-Ag thin film annealed at 200 °C could transform into planar growth structure, and display excellent the highest optical transmittance 89.15% at 550 nm. Meanwhile, the shielding effectiveness (SE) reaches a peak value of 28.1 dB. 500°C is estimated as the threshold annealing temperature of Al-Ag thin film with comprehensive performances gradually declining. Moreover, the Al dopants significantly improve the thermal stability of Ag thin films than that of the pure Ag films. These findings are of important guidance for the preparation of high-quality Al-Ag thin films to meet the practical applications.

Stretchable liquid metal grid/metallized polyurethane composites with switchable electromagnetic interference shielding and efficient infrared stealth performance

Intelligent electromagnetic interference (EMI) shielding materials with tunable electromagnetic shielding properties becomes a significant and urgent concern for information society. Hence, a switchable and low-reflectivity EMI shielding composite is fabricated by electroless nickel plating on the surface of polyurethane nonwoven fabric (Ni@TPU), and followed by combining with liquid metal (LM) grid. The synergistic combination of Ni@TPU and LM grid effectively facilitates the rational construction of hierarchical impedance matching. Meanwhile, it promotes destructive interference between electromagnetic waves reflected from Ni@TPU and the LM grid. As a result, an excellent low-reflectivity EMI shielding performance can be achieved. More importantly, the switchable EMI shielding performance can be easily realized by repeatedly stretching Ni@TPU/LM. In addition, the fluffy nonwoven fabric and LM grid with low infrared emissivity endow it with an outstanding infrared stealth performance. Such excellent low-reflectivity EMI shielding switch performance incorporated with flexible infrared stealth makes it possible to become smart EMI shielding material with a great promise to be employed in the application scenario of window in camouflage container.

Multifunctional composite paper fabricated by graphene oxide/tannin decorated carbon fiber with excellent electromagnetic interference shielding, antibacterial and sound absorption properties

Multifunctional composite paper fabricated by graphene oxide/tannin decorated carbon fiber with excellent electromagnetic interference shielding, antibacterial and sound absorption properties

Making aerogel films like playing LEGO: A universal fabrication strategy for Kevlar based aerogel films with arbitrarily designed functions

Highly flexible, ultrathin and mechanically robust aerogel films activated by functional nanofillers exhibit tremendous potentials for wide applications. However, it is difficult to design different functionalities in a single aerogel film, as different nanofillers often possess opposing properties. Herein, a LEGO®-inspired fabrication strategy to construct Kevlar-based aerogel film with arbitrarily designed functions is introduced by stacking functionalized aerogel film units as stacking LEGO® bricks. The aerogel film units are reliably connected by precursor dispersion-derived LEGO® embossed nodes, leading to superior mechanical strength. Moreover, owing to the flexibility of the LEGO®-inspired assembly method, targeted functions of the aerogel films can be achieved by designing and purposefully combining various stacks. As demonstrations, optimized joule heating, greatly enhanced electromagnetic wave shielding and excellent flame-retardant properties are realized with stacking of different aerogel film units. The unique fabrication strategy opens up opportunities for the design and fabrication of aerogel film with tunable and tailored properties for wide applications.

Highly protective and functional strengthening strategies for 3D printed continuous carbon fiber reinforced polymer composites: manufacturing and properties

Carbon fiber-reinforced polymer (CFRP) composites have gradually emerged as a crucial material in the aerospace industry. However, inadequate impact resistance and thermal stability limit survival in extreme environments. Inspired by the specific functions of multiple layers of tissue, from bird feathers to the musculoskeletal system. We propose low-cost composite strengthening strategies and efficient novel three-dimensional graphene aerogel manufacturing methods. A novel graphene aerogel/carbon fiber reinforced polymer (GAC) composite prepared by in-situ laser-induced graphene (LIG) layers on the surface of 3D-printed CFRP. GAC composites enhance CFRP's impact protection, thermal insulation, and electromagnetic shielding capabilities. For protection, GAC composites reduce low-velocity impact damage by 26.2%. The graphene layer can increase the thermal buffering capacity of the material four times, and the long-term service temperature can be increased by 40% compared to traditional CFRP. For functionality, the composites enable electromagnetic interference (EMI) shielding effectiveness of up to 50.2 dB. Furthermore, it can achieve surface heating above 400 °C and rapid de-icing through electrothermal effects. The simple and efficient processing method of GAC composites and tunable functionalities holds promise for the development of highly protective and intelligent aircraft skins.

Development of Lightweight and Flexible Electromagnetic Shielding Materials using Carbon Nanotube-based Composites

Development of Lightweight and Flexible Electromagnetic Shielding Materials using Carbon Nanotube-based Composites

Revealing synergistic relationship of thermal conduction and electromagnetic shielding of reduced graphene oxide film

The present work tries to explore the evolution process of electro-magnetic interference shielding effectiveness and thermal conductivity of graphene film. There is an obvious promotion of electrical conductivity (from 3.51×10-3 to 769.20 S m-1) when GO is thermally reduced at 1100°C. Correspondingly, the reduced graphene oxide (rGO) achieves the highest EMI shielding effectiveness (∼54.84 dB) at 1100°C which is an synergetic result of electrical conductivity and porous structure with rich defects. The rGO is furtherly graphitized at 2800°C (G-rGO) to repair the defects and C-C network and then mechanically rolled to a densified film with bulk density of 1.64 g cm-3 (called as DG-rGO). The thermal conductivity of DG-rGO membrane increases to 720.56 W m-1 K-1 after graphitization and rolling. Porous structure and defects are beneficial to higher EMI shielding effectiveness while dense structure without defects lead to higher thermal conductivity. Therefore, the highest EMI shielding effectiveness and thermal conductivity cannot be obtained simultaneously. A reference range is provided to fulfill the request of EMI shielding and thermal conductivity.

Chiral Nematic Graphene Films with a mesoporous Structure.

Ordering a crucial material like pure-graphene into the chiral nematic structure can potentially revolutionize the fields of photonics, chiral separation, and energy storage. However, the controlled fabrication of highly ordered graphene films with a long-range chiral nematic mesoporous structure is very challenging and as such, has not been achieved. Here, a chiral-template-directed chemical vapor deposition growth strategy is presented for the precise fabrication of mesoporous chiral nematic graphene films by using nanocrystalline cellulose as templates. It is evidenced that such graphene films possess the left-hand helical ordering, chiral nematic mesoporous structure with adjustable pore sizes (6.4-13.1nm), tailored pitch, excellent electrical conductivity (556 S cm-1), high specific surface area (1508 m2g-1) and mechanical flexibility. By coating Na anode with this film, uniform Na plating is achieved with no dendrite formation, resulting from its unique chiral nematic structure and tunable physicochemical properties. The films also achieved impressive thickness-dependent electromagnetic shielding, i.e., 35-63dB, demonstrating their potentially multi-disciplinary applications.

Conductive Nanocomposites Based on Graphene and Natural Polymers

This thesis focuses on the development of conductive nanocomposite materials based on graphene and natural polymers such as cellulose and chitosan. Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, exhibits exceptional electrical, mechanical, and thermal properties, making it an attractive filler for polymer composites. However, the challenge lies in effectively dispersing graphene sheets within polymer matrices. The work presented explores new strategies for grafting polysaccharide chains onto oxidized graphite (graphene oxide) to improve its compatibility and dispersion in cellulose and chitosan matrices. The resulting composites were doped with gold or nickel nanoparticles to further enhance their electrical and catalytic properties. Detailed characterization techniques, including spectroscopic and microscopic methods, were employed to analyze the structure, morphology, and properties of the developed nanocomposites. The thesis is organized into three main parts: 1) a literature review on graphene, polysaccharides, and their biocomposites; 2) a description of the experimental materials and methods; and 3) a scientific discussion of the results, presented in the form of three research publications. The findings demonstrate the successful synthesis of conductive nanocomposites with improved compatibility and performance, opening up new avenues for the application of these sustainable and multifunctional materials in areas such as electronics, catalysis, and electromagnetic shielding.

Electrical and EMI shielding studies of ferrite/MWCNTs/PVDF composites

AbstractIn this work, CFO/MWCNTs/PVDF and BFO/MWCNTs/PVDF composites are prepared and the comparative analysis of electrical properties and electromagnetic interference (EMI) shielding performance of both type of composites are investigated. The dielectric and conductivity characteristics are observed with varying ferrite concentration, frequency, and temperature. Ferroelectric properties are also obtained at 6 kV/cm field and EMI shielding behavior is observed in 8–12 GHz frequency range. Results exhibited that the studied properties of the composite enhances with increasing ferrite concentration that attributed to increased amount of magnetic nanoparticles. Cobalt ferrite (CFO) filled polyvinylidene fluoride (PVDF) composite is showing better properties as compared to barium ferrite (BFO) filled PVDF composites. The mechanism involve for this behavior is discussed herein.

Replacing the Gallium Oxide Shell with Conductive Ag: Toward a Printable and Recyclable Composite for Highly Stretchable Electronics, Electromagnetic Shielding, and Thermal Interfaces.

Liquid metal (LM)-based composites hold promise for soft electronics due to their high conductivity and fluidic nature. However, the presence of α-Ga2O3 and GaOOH layers around LM droplets impairs conductivity and performance. We tackle this issue by replacing the oxide layer with conductive silver (Ag) using an ultrasonic-assisted galvanic replacement reaction. The Ag-coated nanoparticles form aggregated, porous microparticles that are mixed with styrene-isoprene-styrene (SIS) polymers, resulting in a digitally printable composite with superior electrical conductivity and electromechanical properties compared to conventional fillers. Adding more LM enhances these properties further. The composite achieves EMI shielding effectiveness (SE) exceeding 75 dB in the X-band frequency range, even at 200% strain, meeting stringent military and medical standards. It is applicable in wireless communications and Bluetooth signal blocking and as a thermal interface material (TIM). Additionally, we highlight its recyclability using a biodegradable solvent, underscoring its eco-friendly potential. This composite represents a significant advancement in stretchable electronics and EMI shielding, with implications for wearable and bioelectronic applications.

A Facile Method in Fabricating Flexible Conductive Composites with Large-Size Segregated Structures for Electromagnetic Interference Shielding.

To resist the plastic deformation of polymer particles during hot press molding, high molecular weights, and moduli are required for composites with segregated structures, thus the prepared composites exhibit poor flexibility. Also, larger particle sizes can bring lower percolation thresholds while the ensuing greater deformation destroys the conductive network. Moreover, segregated composites still face preparation complexities. Herein, a facile method for developing flexible composites with large-size segregated structures is proposed. First, silver-coated polydopamine-modified reduced graphene oxide (Ag@PrGO), as conductive fillers, is prepared by electroless plating. Next, polydimethylsiloxane (PDMS)-coated polyolefin elastomer (POE) beads are put into a bag containing the fillers. After a simple shaking, the fillers are adhered to the POE surface as the cohesive property of cured PDMS. Finally, flexible composites with large-size segregated structures are obtained via hot pressing. Benefiting from the 2D structure of the Ag@PrGO and the ability to slip, the conductive networks possess adaptable deformability. The prepared composites exhibit excellent electrical conductivity (203.55 Scm-1) at filler volume fractions of 3.4 vol%. The EMI shielding effectiveness can reach 70dB in the X-band at a thickness of 1.9mm and remains stable after bending and rubbing damage. This work paves the way for constructing large-size segregated structures.

Enhancing metacomposite properties and electromagnetic interference shielding: exploring the interplay between manufacturing processability of carbon fiber elastomeric composite and permittivity/permeability effects

Enhancing metacomposite properties and electromagnetic interference shielding: exploring the interplay between manufacturing processability of carbon fiber elastomeric composite and permittivity/permeability effects