Electromagnetic Wave Shielding Research Articles

All-dielectric structure development for electromagnetic wave shielding using a systematic design approach

Common dielectric metamaterials for electromagnetic (EM) interference shielding, stealth applications, and EM cloaking generally require larger thicknesses than the wavelength of incidence light. We propose an all-dielectric metamaterial inspired structure using a systematic approach based on the phase field design method. The structure is composed of periodically arranged unit structures that have a 2D configuration, which is sub-wavelength thick over its entire structure. The proposed structure provides anomalous reflections to prevent reflections back toward the wave source and is anti-penetrative over the microwave band with no conductive materials. We digitally fabricated the designed structure using 3D printing and verified the design specifications by experiments.

Topology Optimization of an Electromagnetic Wave Shielding Device

Topology Optimization of an Electromagnetic Wave Shielding Device

ANN-Based Two-Layer Absorber Design Using Fe–Al Hybrid Nano-Composites for Broad Bandwidth Microwave Absorption

In the current scenario, the foremost use of microwave absorbers, such as stealth applications and electromagnetic (EM) wave shielding, demands thin and broad bandwidth microwave absorber. In this paper, an attempt is made to fabricate a “cost-effective” composite material, which has good absorption properties, and furthermore, to reduce the coating thickness, the multi-layering approach has been adopted. Because of the excellent magneto-dielectric properties, Fe and Al metal powders were chosen. To see the effect of particle size over microwave absorption property of Fe–Al hybrid nano-composites, the composite was milled for 40 h with an interval of 5 h using the mechano-chemical route. The phase analysis, morphology, and magnetic studies have been carried out for prepared samples and correlated with EM wave properties. The permittivity and permeability values in the frequency range of 4–14 GHz were determined using coaxial reflection/transmission method, and reflection loss (RL) has also been computed. The broad bandwidth of 9.35 GHz (4.65–14 GHz) has been achieved for 40 h milled nano-composite (size ~40 nm) with a coating thickness of 3 mm. For the reduction in the coating thickness, the multi-layering approach has been applied, and an artificial neural network-based method has been proposed to predict each layer thickness and material sequence. The computed results of RL for two-layer absorber exhibit a reduction in the thickness from 3 to 1.96 mm.

Research of glass fibre used in the electromagnetic wave shielding and absorption composite material

Electromagnetic shielding and absorption composite material plays an important role in the defence and economic field. Comparing with other filler, Glass fibre and its processed product—metal-coated glass fibre can greatly reduce the material's weight and costs, while it still remains the high strength and the electromagnetic shielding effectiveness. In this paper, the electromagnetic absorption mechanism and the reflection mechanism have been investigated as a whole, and the shielding effectiveness of the double-layer glass fibre composite material is mainly focused. The relationship between the shielding effectiveness and the filled glass fibre as well as its metal-coated product's parameters has also been studied. From the subsequent coaxial flange and anechoic chamber analysis, it can be confirmed that the peak electromagnetic shielding effectiveness of this double-layer material can reach -78dB while the bandwidth is from 2GHz to 18GHz.

Material Analysis and Application for Radio Frequency Electromagnetic Wave Shielding

In this study, after this introduction, in the second section the electromagnetic shielding concept is discussed. In the third section material selection and applications for an indoor environment, protection against electromagnetic radiation are explained and the results for curtain and fabrics tested for shielding eectiveness are provided. Finally, the paper ends with the conclusions section.

Effect of incorporating carbon nanocoils on the efficiency of electromagnetic-wave shielding of carbon-nanomaterial composites

Carbon nanocoils (CNCs) were deposited on Al2O3 substrates using C2H2 and H2 as source gases in a thermal chemical vapor deposition system. Composites of CNCs in polyurethane (CNC@PU) and CNCs plus other carbon-based materials, such as carbon microcoils (CMCs) and carbon nanotubes (CNTs), in polyurethane (CNC+CMC@PU, CNC+CNT@PU) was fabricated. The electromagnetic-wave-shielding effectiveness of the CNCs-incorporated composites were examined and compared with those of other carbon-based materials in the measurement-frequency range of 0.25–4.0GHz. The incorporation of CNCs in CMC@PU composites reduced the shielding effectiveness; on the other hand, it slightly enhanced the shielding effectiveness of CNT@PU composites within the measurement frequency range of 0.5–3.0GHz. Based on the resulting shielding effectiveness, we conclude that the incorporation of CNCs was useful for the materials that exhibited reflection-based shielding effectiveness although the CNCs themselves had poor electrical conductivity.

Effectiveness of Electromagnetic-Wave Shielding by Composites of Carbon Nanotubes and Carbon Microcoils in Polyurethane.

Carbon microcoils (CMCs) were deposited on Al2O3 substrates using C2H2 and H2 as source gases and SF6 as an additive gas in a thermal chemical vapor deposition system. Composites of carbon nanotubes in polyurethane (CNT@PU), carbon microcoils in polyurethane (CMC@PU), and carbon nanotubes plus carbon microcoils in polyurethane (CNT + CMC@PU) were fabricated. The electromagnetic-wave-shielding properties of the CNT + CMC@PU composites were examined and compared with those of CNT@PU and CMC@PU in the measurement-frequency range of 0.25-3.5 GHz. By the incorporation of CNTs, the CNT + CMC@PU composite had the reduced volume resistivity compared with that of CMC@PU composite. Consequently it gives rise to the enhanced shielding effectiveness through the reflection-based EMI-shielding mechanism. Meanwhile, the CNT + CMC@PU composite showed increasing shielding effectiveness with increasing measuring frequency in the range of 2.0-3.5 GHz. In addition, the CNT+CMC@PU composite's SE increased with increasing coated-layer thickness. These results indicate the role of the absorption as an EMI-shielding mechanism in CNT + CMC@PU composite. Based on these results, we suggest that the CNT + CMC@PU composite is a promising EMI-shielding material that can be applicable in a wide frequency range through the reflection and absorption shielding mechanism.

Preparation and Study on Nickel Oxide Reduction of Polyacrylonitrile-Based Carbon Nanofibers by Thermal Treatment.

Carbon materials containing magnetic nanopowder have been attractive in technological applications such as electrochemical capacitors and electromagnetic wave shielding. In this study, polyacrylonitrile (PAN) fibers containing nickel nanoparticles were prepared using an electrospinning method and thermal stabilization. The reduction of nickel oxide was investigated under a nitrogen atmosphere within a temperature range of 600 to 1,000 °C. Carbon nanofibers containing nickel nanoparticles were characterized by FE-SEM, EDS, XRD, TGA, and VSM. It was found that nickel nanoparticles were formed by a NiO reduction in PAN as a function of the thermal treatment. These results led to an increase in the coercivity of nanofibers and a decrease in the remanence magnetization.

Investigation of the Electromagnetic Shielding Effectiveness of Carded and Needle Bonded Nonwoven Fabrics Produced at Different Ratios with Conductive Steel Fibers

The number of electrical and electronic devices in our daily life has increased. The devices produce electromagnetic waves which harm human and environments. In recent years, there has been an increasing interest in the reduction and control of electromagnetic waves. The paper focuses on shielding of electromagnetic waves of nonwoven fabrics produced with needle punching technology from conductive stainless steel fibers. The needle punched nonwoven fabrics were produced with carding and needle punching technology by blending stainless steel fibers and normal staple polyester fibers at different ratios for electromagnetic shielding applications. The electromagnetic shielding effectiveness of the nonwoven fabrics with conductive stainless steel fibers was tested. After blending of stainless steel fibers and normal polyester fibers, the webs were formed by a wool-type carding machine and the after web folding operation, the webs were bonded by needle punching at constant working parameters. During production, the needle punch densities per cm2 and needle penetration depth per mm were kept constant. Bulky needle punched nonwoven fabrics with low needling density were produced. The main objective of our research was to develop the nonwoven fabric for shielding against electromagnetic waves. In addition, the effect of the stainless steel fiber ratio used in the needle punched nonwoven fabrics on electromagnetic shielding effectiveness was investigated. After production, the thicknesses of the needle punched nonwoven fabrics were tested. The electromagnetic shielding effectiveness, reflection and absorption values of the needle punched nonwoven fabric samples were measured at the frequency range of 15-3000MHz and presented in table and graphics. As the ratio of stainless steel fibers used in the nonwoven fabric increased, Electromagnetic shielding effectiveness values (EMSE) were increased in a linear manner and obtained results were discussed. It was found that the electromagnetic waves were shielded about 90% at high frequencies, 85% at medium frequencies, and 80% at low frequencies by needle punched nonwoven fabric with 5% conductive stainless steel fiber. The EMSE values such as 20dB, 25dB and 45dB were obtained at low frequency ranges (0–300MHz and 25dB, medium frequency ranges, 300-1200MHz and 45dB, and high frequency ranges, 1200-3000MHz) with the needle punched nonwoven fabric containing 25% conductive stainless steel fiber.

Enhancement of the Electromagnetic Wave Shielding Effectiveness by Geometry-Controlled Carbon Coils

Carbon microcoils were deposited onto Al2O3 substrates using C2H2/H2 as source gases and SF6 as an incorporated additive gas in a thermal chemical vapor deposition system. At as-grown state, the carbon coils (d-CCs) show the diverse geometry. The geometry-controlled carbon microcoils (g-CMCs) could be obtained by manipulating the injection time of SF6 in C2H2 source gas. The d-CCs with polyurethane (PU) composite (d-CC@PU) and the g-CMCs with PU composite (g-CMC@PU) were obtained by dispersing d-CCs and g-CMCs in PU, respectively. The electromagnetic wave shielding properties of d-CC@PU and g-CMC@PU composites were investigated in the frequency range of 0.25 - 4.0 GHz. The shielding effectiveness (SE) of d-CC@PU and g-CMC@PU composites were measured and discussed according to the weight percent of d-CCs and g-CMCs in the composites with the thickness of the composites layers. On the whole frequency range in this work, the SE of g-CMC@PU composites was higher than those of d-CC@PU composites, irrespective of the weight percent of carbon coils in the composites and the layer thickness. Furthermore, we confirmed that the absorption mechanism, instead of the reflection mechanism, seemed to play the critical role to shield the EMI for not only the g-CMC@PU composites but also the d-CC@PU composites.

炭素粉末を添加したモルタルの電磁波遮へい性に関する研究

炭素粉末を添加したモルタルの電磁波遮へい性に関する研究

171 農業系副産物を配合したプラスチックシート材の電磁波吸収・シールド特性

171 農業系副産物を配合したプラスチックシート材の電磁波吸収・シールド特性

Electromagnetic Wave Shielding Effectiveness Based on Carbon Microcoil‐Polyurethane Composites

Carbon microcoils (CMCs) were deposited onto Al2O3 substrates using C2H2/H2 as source gases and SF6 as an incorporated additive gas in a thermal chemical vapor deposition system. CMC‐polyurethane (PU) composites were obtained by dispersing the CMCs in the PU with a dimethylformamide additive. The electromagnetic wave shielding properties of the CMC‐PU composites were examined in the frequency range of 0.25–1.5 GHz. The shielding effectiveness (SE) of the CMCs‐PU systematically increases with increasing the content of CMCs and/or the layer thickness. Based on these results, the main SE mechanism for this work was suggested and discussed.

Radar Absorbing Material (RAM)

This paper briefly outlines the research and development activities in radar absorbing materials. Military defense scientists to the possibility of using coating materials to render aircraft or other military vehicles less visible to radar and, preferably, to control such visibility. The highly conducting surface of a metal vehicle is an excellent reflector of radar, but an absorbing layer would suppress the radar signal at the receiver station. Radar absorbing material currently in military and commercial use are typically composed of high concentrations of iron powders in a polymer matrix. These materials are both very heavy and very costly, two key limitations to their adoption for many applications. The performance of these coatings, particularly those using spherical particles, is dependent upon how closely the spheres are packed together. Thus the most efficient coating would be one approaching the density of solid iron with a minimum amount of resin included to electrically insulate the particles from one another. That is, the attenuation efficiency increases faster than the weight, so that a thinner coating with the same attenuation, can be used, providing an overall weight savings. Unfortunately, the particles, when produced, are of non-uniform diameter and not necessarily uniformly round. A window member composed of a transparent resin or inorganic glass with a transparent conducting film such as gold or ITO coated, is used as an electromagnetic wave shield window for stealth aircraft. However, the transparent conducting film, especially ceramic transparent conducting film such as ITO does not deform sufficiently to follow the deformation of the window material. Therefore the transparent conducting film might crack even with relatively little deformation, which can occur during an actual flight.

Effect of Technological Parameters on Preparation of Mg-Based Foam Materials

As a novel material, Mg-based foam material not only has fantastic physical characteristics, such as low density, high specific surface area, high specific strength and stiffness, and good biocompatibility, but also has special functional properties, for example, electromagnetic wave shielding, vibration reduction, sound absorption, and so on. It can be widely applied to aeronautical and aerospace, military, shipbuilding, transportation, automotive and medical industries. Mg-based foam material was prepared by direct foaming in magnesium alloy liquid in this study, and the effect of technological parameters on the products, such as addition amount of and granularity of SiC particles and MgCO3 particles, stirring temperature, stirring time, stirring velocity, foaming temperature and foaming time, was investigated. The aim of this research was to develop a new technology which could fabricate large scale Mg-based foam material in air condition. The results showed that variations of technological parameters may affect preparation of the foam materials in some extent and resulted in the changes of the products in apparent density, porosity and structural uniformity. The light weight Mg-based foam with homogeneous pores could be obtained by suitable combination of the technological parameters.

Acoustic-based wireless signal transmission for precision metrology: Accuracy and reliability

Metallic shielding of electromagnetic waves presents a roadblock for machine tool and process monitoring. Acoustic waves, alternatively, provide a viable mechanism, due to their inherent transmissibility in metals. This paper presents a quantitative analysis of factors affecting the performance of acoustic-based signal transmission including carrier frequency, bandwidth, signal-to-noise ratio, data bit-rate, etc. Signal attenuation and data loss due to wave diffraction and reflection is first numerically studied using finite element models of representative machine structures. Experimental evaluation of these models with operating production machinery quantifies the accuracy and reliability of in situ acoustic signal transmission methods for precision metrology in manufacturing.

ULTRA WIDE BAND RESPONSE OF AN ELECTROMAGNETIC WAVE SHIELD BASED ON A DIODE GRID

This paper investigates Ultra Wide Band (UWB) response of a self-actuated electromagnetic wave shield based on a diode grid both in frequency and time domain. The investigation is flrst carried out on a shield valid for an incident wave polarized at a speciflc direction only, then extended to a shield efiective for an incident wave polarized at an arbitrary direction. In the frequency domain, two linear analysis methods are used to study the properties of the diode grid over the frequency range from 0.01 to 10GHz. One method is the microwave network analysis. Another is simulating the diode grid by a linear equivalent circuit instead of a diode. In the time domain, the property of the shield is studied with respect to a broadband impulse, where the diode is described by its SPICE circuit model including the nonlinear property. The results show that the diode grid works well as a self-actuated electromagnetic power selective surface (PSS) in a certain frequency range. The diode grid is strongly frequency dependent. The operating frequency band relies on the reactive elements in the diode grid. In order to extend the operating frequency to a high band, smaller cell size and smaller junction capacitance should be employed.

Al3+와 Y3+동시치환 SnO2투명전극 박막의 전기적 특성

Transparent conducting oxides (TCOs) have wide range of application areas in transparent electrode for display devices, Transparent coating for solar energy heat mirrors, and electromagnetic wave shield. is intrinsically an n-type semiconductor due to oxygen deficiencies and has a high energy-band gap more than 3.5 eV. It is known as a transparent conducting oxide because of its low resistivity of and high transmittance over 90% in visible region. In this study, co-doping effects of Al and Y on the properties of were investigated. The addition of Y in was tried to create oxygen vacancies that increase the diffusivity of oxygen ions for the densification of . The addition of Al was expected to increase the electron concentration. Once, we observed solubility limit of single-doped with Al and Y. was used for the source of Al and Y to prevent the evaporation of and for the charge compensation. And we observed the valence changes of aluminium oxide because generally reported of valence changes of aluminium oxide in Tin - Aluminium binary system. The electrical properties, solubility limit, densification and microstructure of co-doped with Al and Y will be discussed.

Preparation, characterization and microwave absorption properties of barium-ferrite-coated fly-ash cenospheres

Magnetic composites of barium ferrite coated on fly-ash cenospheres (BFACs) were prepared by sol–gel auto-combustion method. To promote surface activity, we modified fly-ash cenospheres (FACs) surfaces using γ-aminopropyltriethoxysilane (APS) as coupling agent and silver nitrate as activating agent before coating barium ferrite films on FACs. The morphology, composition, crystal structure, magnetic and microwave absorption properties of these composite powders were characterized by scanning electron microscope, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer, and vector network analyzer. Continuous and uniform coatings of barium ferrite were found on the surfaces of the FACs. The BFACs powders-epoxy composite possesses excellent microwave absorption properties in the 2–18GHz frequency range. The maximum microwave reflection loss reaches −15.4dB at 8.4GHz with a thickness of 3.0mm, and the widest bandwidth less than −12dB is 6.2GHz with a sample thickness of 2.0mm. The intrinsic reasons for microwave absorption were also investigated. Applications of this composite material in magnetic recording, electromagnetic wave shielding, and lightweight microwave-absorbing fields are promising.

Electromagnetic shielding mechanisms using soft magnetic stainless steel fiber enabled polyester textiles

This work studied the effects of conductivity, magnetic loss, and complex permittivity when using blended textiles (SSF/PET) of polyester fibers (PET) with stainless steel fibers (SSF) on electromagnetic wave shielding mechanisms at electromagnetic wave frequencies ranging from 30MHz to 1500MHz. The 316L stainless steel fiber used in this study had 38vol% γ austenite and 62vol% α′ martensite crystalline phases, which was characterized by an x-ray diffractometer. Due to the magnetic and dielectric loss of soft metallic magnetic stainless steel fiber enabled polyester textiles, the relationship between the reflection/absorption/transmission behaviors of the electromagnetic wave and the electrical/magnetic/dielectric properties of the SSF and SSF/PET fabrics was analyzed. Our results showed that the electromagnetic interference shielding of the SSF/PET textiles show an absorption-dominant mechanism, which attributed to the dielectric loss and the magnetic loss at a lower frequency and attributed to the magnetic loss at a higher frequency, respectively.