Electromagnetic Wave Shielding Research Articles

Terahertz time-domain spectroscopy of thin and flexible CNT-modified MXene/polymer composites

Herein, we report terahertz (THz) shielding of flexible MXene (Ti3C2Tx)/MWCNT/PVA polymer composite films by using THz time-domain spectroscopy (THz-TDS) in 0.1–2.0 THz frequency range. The polymer composite with 42 µm thickness exhibited an excellent shielding effectiveness of 36 dB at 2 THz which is much higher than most of the reported materials for THz shielding with comparable thickness. The absorption coefficient increases from 100 cm−1 for pristine PVA to ~ 600 cm−1 for 20 wt% MXene/1.5 wt% MWCNT/PVA composite. The high THz shielding of flexible MXene/MWCNT/polymer composite is ascribed to the good electrical conductivity and interfacial synergistic effect of 1D/2D nanostructures that promoted the shielding of electromagnetic waves. Our simple solution casting methodology for fabrication of thin films and subsequent high THz shielding opens possibilities to design MXene-based polymer composites for THz applications.

3D cross-linked graphene or/and MXene based nanomaterials for electromagnetic wave absorbing and shielding

With the rapid digitalization and technological advancements of the modern society, the seriously increasing electromagnetic pollution has created stronger demand for advanced electromagnetic wave shielding and absorbing materials in both civilian and military fields. Multifunctional materials with ultra-lightweight, wide bandwidth, highly flexible and robustness are the future development direction to meet the applications. Graphene and MXene, as two typical 2D nanomaterials, have attracted considerable interests for the electromagnetic wave shielding and absorbing materials. More importantly, three dimensional (3D) cross-linked graphene or/and MXene based materials, where graphene or/and MXene sheets are interconnected into a macroscopic monolithic bulk material, can achieve excellent electromagnetic interference (EMI) shielding and microwave absorption (MA) performance, together with lightweight, exceptional mechanical properties and so on. This review addresses the construction methods of graphene and MXene based 3D cross-linked materials, and the effects of different fabrication methods toward the structure and EMI shielding and/or MA properties are discussed. Additionally, some perceptions and discussions are proposed for the future studies.

액체 소금물을 이용한 투명 전자파 차폐

Transparent antennas and electromagnetic-wave shielding using existing optically transparent electrodes (TEs) such as indium tin oxide, MLF, and metal mesh were investigated. We analyzed the optical and electrical characteristics of a liquid TE using saltwater compared to those of conventional solid TEs. Saltwater with a salinity of 35 ppt (conductivity=5 s/m) has an average transparency of >95% in the visible band. A planar saltwater layer with a 3 mm thickness has a shielding effectiveness performance of >22 dB.

Accurately Engineering 2D/2D/0D Heterojunction In Hierarchical Ti3C2Tx MXene Nanoarchitectures for Electromagnetic Wave Absorption and Shielding.

The accurate heterojunction engineering in MXene-based composites unprecedentedly boosts their electromagnetic (EM) wave absorption and shielding performance. However, the flocculation of MXene caused by abundant termination groups severely restricts the regulation of heterojunction, which hankers for a revolutionary compositing strategy against unmanageable self-aggregation. Herein, electrically neutral coordination compound with large molecular volume is decorated on Ti3C2Tx lamellas to protect them from self-precipitation. A rapid polymerization reaction then controllably assembles them into a hierarchical microsphere composed of superlattice-like 2D/2D polymer/MXene building blocks. In the carbonized Ti3C2Tx/C/MoO2 microspheres, 2D/2D/0D heterojunctions can be precisely tuned to regulate electric/dielectric properties. These heterojunctions simultaneously trigger the intensive interfacial polarization and out-plane electron flowing to exhaust the EM energy as much as possible, confirmed by electron holography. Therefore, our products achieve the first-rate EM wave absorption with an ultrabroad absorption bandwidth of 7.7 GHz at the thickness of 2.5 mm. By altering the heterojunction, the composite acquires excellent EM interference shielding performance with an average shielding effectiveness of 35.9 dB. These accomplishments light a new way to microstructure construction and heterojunction design of MXene-based composites and lay out a profound insight into their EM wave absorption mechanism.

Cost Effective and Sustainable Test Methods to Investigate Vulnerabilities of EMP Attack on Existing Buildings Using Public Frequency Devices

High-power electromagnetic pulses are electromagnetic shock waves with strong energy, which can cause the destruction or malfunction of both electrical and electronic systems. The measurement of the electromagnetic wave shielding performance of buildings is effective for determining the level of EMP protection for each facility. However, it is extremely inefficient to practically measure the electromagnetic wave shielding performance using methods based on various standards for general buildings, in term of testing cost and time. Therefore, cost effective and sustainable test methods to investigate vulnerabilities of electromagnetic pulses attack on existing buildings using public frequency is proposed in this study. The study focuses on a simpler and more reliable method such as the use of broadcast or communication signals. From the results, it was concluded that the shielding performance can be measured approximately −45 dB using broadcast devices, −70 dB using walkie-talkie as simplified measurements of the electromagnetic-wave shielding performance. Therefore, if the test methods which are proposed in this study are allowed for preliminary investigation to find the vulnerabilities of existing buildings, cost and energy in the investigation can be reduced and it is expected to bring out frequency inspection and sustainable EMP protection performance of buildings.

Polyaniline/oxide-based core-shell like structured composites for reduction in electromagnetic pollution

Polyaniline (PANI) based composites with manganese dioxide (MnO2, 30 wt.%) and vanadium pentaoxide (V2O5, 30 wt.%) have been synthesized using the in-situ polymerization synthesis route, whereas both the oxides used as filler materials in the polyaniline matrix. The amalgamated composites have been analyzed for morphological investigation and shielding the incident electromagnetic (EM) waves in the frequency range 8.2-12.4 GHz (X-band). PANI/MnO2 and PANI/V2O5 composites are synthesized in core-shell like morphology, whereas PANI act as core while oxide act as the shell. The shielding of EM waves has been investigated in terms of shielding effectiveness (SE). PANI/MnO2 composite exhibits the efficient SE value i.e. ~50 dB as shown in the figure. This higher value of SE is due to the ferromagnetic character of MnO2 particles which increases the dielectric losses in the specimen. Whereas, PANI/V2O5 composite attain the smaller value of SE i.e. ~9 dB, because V2O5 particles are diamagnetic in nature, thus dielectric losses decrease. Moreover, SE decreases with an increase in frequency due to a decrease in dielectric losses. PANI/MnO2 composite has an SE value greater than the minimum requirement for industrial application i.e. 30 dB, thus, PANI/MnO2 composite can be used as EM shielding material, whereas, PANI/V2O5 composite can’t fulfill this requirement.

One pot facile transformation of CO2 to an unusual 3-D nano-scaffold morphology of carbon

An electrosynthesis is presented to transform CO2 into an unusual nano and micron dimensioned morphology of carbon, termed Carbon Nano-Scaffold (CNS) with wide a range of high surface area graphene potential usages including batteries, supercapacitors, compression devices, electromagnetic wave shielding and sensors. Current CNS value is over $323 per milligram. The morphology consists of a series of asymmetric 20 to 100 nm thick flat multilayer graphene platelets 2 to 20 µm long orthogonally oriented in a 3D neoplasticism-like geometry, and appears distinct from the honeycomb, foam, or balsa wood cell structures previously attributed to carbon scaffolds. The CNS synthesis splits CO2 by electrolysis in molten carbonate and has a carbon negative footprint. It is observed that transition metal nucleated, high yield growth of carbon nanotubes (CNTs) is inhibited in electrolytes containing over 50 wt% of sodium or 30 wt% of potassium carbonate, or at electrolysis temperatures less than 700 °C. Here, it is found that a lower temperature of synthesis, lower concentrations of lithium carbonate, and higher current density promotes CNS growth while suppressing CNT growth. Electrolyte conditions of 50 wt% sodium carbonate relative to lithium carbonate at an electrolysis temperature of 670 °C produced over 80% of the CNS desired product at 85% faradaic efficiency with a Muntz brass cathode and an Inconel anode.

Influence of carbon fiber additions on the electromagnetic wave shielding characteristics of CNT-cement composites

This study examined the synergistic effect of carbon fiber (CF) addition on the electromagnetic wave shielding characteristics of carbon nanotube (CNT)-cement composites. Effect of the amount and length of CF on the electrical conductivity, electromagnetic interference (EMI) shielding effectiveness (SE), and complex permittivity of the composites were systematically investigated. The electrical conductivity was determined by means of a digital multimeter, and a network analyzer was used to measure the EMI SE and complex permittivity of the composites in the frequency range of 0.1 to 18 GHz. The electrical conductivity and complex permittivity of the composites incorporating 3 mm CF or 6 mm CF were shown to be proportional to the CF content, while the effect of CF length on the EMI SE was more pronounced as the CF length increased from 0.1 mm (aspect ratio 14) to 3 mm (aspect ratio 417). Enlargement of the aspect ratio of CF led to the enhancement of electrical conductivity and absorption loss of the composites, attributing to a notable increase in the SE.

Construction of Ni-loaded ceramic composites for efficient microwave absorption

To realize the high-effective utilization of solid waste fly ash (FA) as microwave absorbent, the Ni-loaded FA composites (NiFA) used as microwave absorbents were synthesized by a two-step method using solid waste fly ash as the raw material. The experiments included the synthesis of FA-based ceramic matrix, loading Ni2+ and the heat-treatment process at different annealing temperatures. According to the XRD and SEM results, the pyrolysis products of nickel nitrate and/or the products from the carbothermal reduction were dispersed over interior and surface of ceramic matrix. For NiFA700 composite, the minimum reflection loss (RLmin) value reached −45.7 dB and the effective bandwidth (RL ≤ −10 dB) was 4.6 GHz when the coating thickness was 1.6 mm. The superior microwave absorption (MA) performance could be ascribed to the good impedance matching and polarization effect resulting from the interface between Ni particles and matrix. Therefore, this study not only provides a potential microwave absorber for application in the field of electromagnetic wave absorption and shielding, but also develops a novel utilization avenue for fly ash.

The Effects of Productization, Organizational, Overseas Market Adaptation Competences on Export Performance: Focus on Korean Electromagnetic Wave Shielding Firms

The Effects of Productization, Organizational, Overseas Market Adaptation Competences on Export Performance: Focus on Korean Electromagnetic Wave Shielding Firms

High-performance copper mesh for optically transparent electromagnetic interference shielding

A wide-spectrum high-transmittance copper mesh was designed and fabricated for effective shielding of electromagnetic waves. Using mask lithography and chemical etching, the copper mesh can be easily fabricated. The thickness of the copper mesh is uniform, whether at the crossing section and the copper wire. The average transmittance of the copper mesh from ultraviolet band to near-infrared band (200–2500 nm) is 96%, in agreement with the designed results. The electromagnetic interference shielding efficiency (EMI SE) is to 16 dB in Ku-band. The result of X-ray photoelectron spectroscopy analysis shows that a large amount of Cu2+ on the surface is reduced to Cu0 and Cu+ after annealing. As result, the EMI SE value of copper mesh has increased by 1.5 dB in Ku-band. We envision that the copper mesh can provide a good solution for optically transparent electromagnetic interference shielding.

Electromagnetic wave shielding/absorption performances of cementitious composites incorporating carbon nanotube metamaterial with helical chirality

Helical carbon nanotubes, a type of chiral metamaterial, were employed to investigate their effects as well as the mechanisms to electromagnetic wave shielding and absorption performances of cementitious composites over the frequency range from 2 GHz to 18 GHz. The results demonstrate that the best electromagnetic wave shielding effectiveness (SE) of cementitious composites filled with 7.5 wt.% helical carbon nanotubes is 1.39 times of that of cementitious composites without helical carbon nanotubes. The minimum reflectivity in 20 mm-thickness cementitious composites with 4.5 wt.% helical carbon nanotubes is 2.7 times of that of cementitious composites without helical carbon nanotubes. Cementitious composites with 7.5 wt.% helical carbon nanotubes have smallest matching thickness and the minimum reflectivity of −41.0 dB. By analyzing electromagnetic parameters and conductive mechanisms, it is found that helical carbon nanotubes mainly affect reflection loss ratio in electromagnetic wave shielding and the dielectric loss in electromagnetic wave absorption. Both parameters are attributed to the enhanced conductivity with the increase of helical carbon nanotubes. The percolation zone ranges from 1.5 wt.% to 7.5 wt.% for alternating current resistivity, with conductive path transferring from ion conduction to electron conduction as the content of helical carbon nanotubes increases. Additionally, incorporating helical carbon nanotubes essentially does not cause the decrease in compressive strength of cementitious composites. The results recommend that cementitious composites incorporating carbon nanotube metamaterial with helical chirality present high electromagnetic performances with satisfactory compressive strength.

Light-weight and high-efficiency electromagnetic wave shielding properties based on waste straw porous carbon

Light-weight and high-efficiency electromagnetic interference (EMI) shielding materials have drawn attention. Porous carbon was prepared by waste wheat straw as well as the electromagnetic shielding performance was investigated. The products have a large specific surface area owing to their porous structure. The straw carbon (SC) was prepared at 900 °C called SC-900 °C with a specific surface area of 78.98 m2 g−1 and exhibited a enhanced electromagnetic shielding performance. The average SET value of SC-900 °C is 16.79 dB with 2.0 mm thickness, and it increases to 47.58 dB with 5.0 mm thickness. EMI SE mainly comes from SEA, which means that the absorption plays a dominated role in the shielding mechanism for SC-900 °C material. The excellent electromagnetic shielding performance of SC-900 °C results from the absorption process, the special three-dimensional porous structure, the multiple polarization and scattering, interfacial polarization, as well as the impedance matching. The results show that the SC-900 °C with strong absorption, wide band, and thin thickness can be used as a promising electromagnetic wave absorber.

Electromagnetic Shielding of Monolayer MXene Assemblies.

Miniaturization of electronics demands electromagnetic interference (EMI) shielding of nanoscale dimension. The authors report a systematic exploration of EMI shielding behavior of 2D Ti3 C2 Tx MXene assembled films over a broad range of film thicknesses, monolayer by monolayer. Theoretical models are used to explain the shielding mechanism below skin depth, where multiple reflection becomes significant, along with the surface reflection and bulk absorption of electromagnetic radiation. While a monolayer assembled film offers ≈20% shielding of electromagnetic waves, a 24-layer film of ≈55 nm thickness demonstrates 99% shielding (20 dB), revealing an extraordinarily large absolute shielding effectiveness (3.89 × 106 dB cm2 g-1 ). This remarkable performance of nanometer-thin solution processable MXene proposes a paradigm shift in shielding of lightweight, portable, and compact next-generation electronic devices.

Integrated multifunctional macrostructures for electromagnetic wave absorption and shielding

This review comprehensively introduced the electromagnetic wave absorbing and shielding (EMAS) materials with macrostructures and the multifunctionality of some advanced EMAS materials.

Wireless Power-Data Transmission for Industrial Internet of Things: Simulations and Experiments

One of the key challenges in the practical realization of industrial internet of things (IoT) is overcoming Faraday shielding of free space electromagnetic waves emanating from the antennas of wireless systems used for power and data transfer. Metallic structures, machinery, pipeline, etc., cause interference resulting in the loss of signal connectivity among sensor network. Currently available techniques based on ultrasonic-electromagnetic transducers pose severe limitations on frequency, efficiency, and alignment. Here we demonstrate exciting Zenneck type interface waves propagating as localized charge oscillations (modes) along the metal profile, which overcomes the restrictions on frequency, metal obstacles, partial enclosures, and alignment. A finite element methods (FEM) model developed to predict the signal reception and power transfer efficiency across metal infrastructure shows excellent agreement with the experimental results. Electrical power transfer using Zenneck, under open conditions, show 4% drop for distance of 1 to 8 meters (68 to 64%), and 9% drop under shielded conditions for the same range (66 to 57%). For data transmission results, we demonstrate a feasibility, for an input power of 0dBm with several metallic pipelines as obstacles show received power of -11.8 dBm and -19.01 dBm at 6 and 25 meters, respectively.

Flexible PVDF/carbon materials/Ni composite films maintaining strong electromagnetic wave shielding under cyclic microwave irradiation

In current work, multiwalled carbon nanotubes (MWCNTs), graphene nanoplatelets (GnPs) and nickel (Ni chains or flowers) were evenly dispersed in poly(vinylidene fluoride) (PVDF) matrices to fabricate composite flexible films.

Conducting polyaniline based rubber nanocomposites – Synthesis and characterization studies

Dielectric polymer nanocomposites are extensively used in electronics and power systems due to their high breakdown strength, resilience and their capability to adapt any desired shape, moreover conducting flexible nanocomposites based on rubber is a promising material for electromagnetic wave shielding and dielectric materials. The prime objective of the study was to synthesize polyaniline (PAni) in a modest and cost-effective way, its characterization and composite preparation based on this synthesized PAni. The prepared PAni was characterized using Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and X Ray Diffraction (XRD) to authorize the formation and particle magnitude. PAni was inserted into natural rubber matrix using conventional method of mixing at different proportions. The selection of natural rubber as matrix was mainly due to its superior flexibility, resilience and elasticity. Conductivity increases fivefold upon the addition of 20% PAni to rubber matrix. The dielectric properties were studied at the desired frequency range. Dielectric studies show that permittivity as well as tan delta values increases with filler loading.

A Study on the Heating Characteristic and Electromagnetic Wave Shielding Carbon Fiber Mat

A Study on the Heating Characteristic and Electromagnetic Wave Shielding Carbon Fiber Mat

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

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