Resonance suppression and electromagnetic shielding effectiveness improvement of an apertured rectangular cavity by using wall losses

The cavity-mode resonance effect could result in significant degradation of the shielding effectiveness （SE） of a shielding enclosure around its resonance frequencies. In this paper, the influence of coated wall loss on the suppression of the resonance effect is investigated. For this purpose, an equivalent circuit model is employed to analyze the SE of an apertured rectangular cavity coated with an inside layer of resistive material. The model is developed by extending Robinson＇s equivalent circuit model through incorporating the effect of the wall loss into both the propagation constant and the characteristic impedance of the waveguide. Calculation results show that the wall loss could lead to great improvement on the SE for frequencies near the resonance but almost no effect on the SE for frequencies far away from the resonance.

Modeling of Material Shielding Effectiveness Against Electromagnetic Pulse in Time-domain

To characterize the shielding effectiveness(SE) of materials against electromagnetic pulse(EMP) that cannot be adequately evaluated by traditional test methods,a transfer function model of SE is proposed.Using homemade broadband coaxial fixture,the SE of a metal fabric material against square-pulse and electrostatic discharge(ESD) EMP is tested in the time domain.The peak SE calculated from the test results matches well with that obtained theoretically.Based on the system identification theory,we propose the transfer function model of SE,which takes the square pulse and human body model ESD EMP data obtained in the tests as training data and takes the machine model as verification data,as well as a second-order expression of the transfer function.Using the transfer function model,the waveforms of the shield-penetrated square-pulse EMP and the ESD EMP are actually predicted.From the perspective of system identification,this accurate prediction of the shielded waveform of EMP provides a reliable way for evaluating SE of materials against EMP.

Study on Electromagnetic Shielding Effectiveness of Ni-P-La Alloy Coatings

Ni-P and Ni-P-La alloy coatings were prepared by electroplating. Electromagnetic shielding effectiveness under the different components of rare earth or the different operating conditions was tested by the network analyzer. The results show that electromagnetic shielding effectiveness of Ni-P-La alloy coating varies from 45 dB to 70 dB with the variety of the frequency from 10 MHz to 350 MHz. Corrosion of the salt fog impacts on the electromagnetic shielding effectiveness a little. A small amount of rare earth added to plating bath can not only enhance corrosion resistance of coating, but make electromagnetic shielding effectiveness increase by 1 ~ 5 dB.

Study on Shielding Effectiveness of Fabric for Electromagnetic Wave with Different Inlaid Distances of Metal Fibres

The electremagnetic radicalization has become more serious. The shielding effectiveness of polyester fabrics with different inlaid distance of parallel metal fibres to electromagnetic wave was studied in this paper on special instrument made by ourselves. The results of test show that the fabric with different inlaid distances of metal fibres and the testing angle between electric field plane and parallel metal fibres of have obvious effect on the shielding effectiveness of electromagnetic wave.

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.

Analysis of Reflectivity and Shielding Effectiveness of Absorbing Material–Conductor Laminate for Electromagnetic Compatibility

An absorbing material–conductor laminate is widely used for electromagnetic compatibility of electronic circuits at microwave frequencies. Such a laminate when properly designed will exhibit good results in terms of electromagnetic interference and compatibility. In this paper, microwave absorbing materials like 1) Ca-NiTi hexa ferrite composites (Ca (NiTi)x Fe12-2xO19) for x = 0.4, 2) M-Type Barium ferrites (BaFe12-2xAxCoxO19 for the tetravalent A ions, Ru4+ is chosen), 3) MnZn ferrite-Rubber composites with volume fraction vf = 0.4, 4) Carbonyl-Iron particle composites with volume fraction vf = 40% and conducting materials like copper, stainless steel are considered to form the interface in the laminate. Mathematical formulations are carried out for the estimation of reflectivity and shielding effectiveness of absorbing material–conductor laminate at microwave frequencies Analysis is also carried out for various thicknesses of the microwave absorbing material and conducting material in the laminate. The reflectivity and shielding effectiveness depends not only on the type of the selected material in the laminate, but also their thickness in the laminate and frequency of operation.

A transparent electromagnetic-shielding film based on one-dimensional metal–dielectric periodic structures

In this study, we designed and fabricated optical materials consisting of alternating ITO and Ag layers. This approach is considered to be a promising way to obtain a light-weight, ultrathin and transparent shielding medium, which not only transmits visible light but also inhibits the transmission of microwaves, despite the fact that the total thickness of the Ag film is much larger than the skin depth in the visible range and less than that in the microwave region. Theoretical results suggest that a high dielectric/metal thickness ratio can enhance the broadband and improve the transmittance in the optical range. Accordingly, the central wavelength was found to be red-shifted with increasing dielectric/metal thickness ratio. A physical mechanism behind the controlling transmission of visible light is also proposed. Meanwhile, the electromagnetic shielding effectiveness of the prepared structures was found to exceed 40 dB in the range from 0.1 GHz to 18 GHz, even reaching up to 70 dB at 0.1 GHz, which is far higher than that of a single ITO film of the same thickness.

Experimental Data for Study on the Shielding Effect of Electromagnetic Wave

This article presents some new experimental data for study the shielding effect of electromagnetic wave. The frequencies of electromagnetic wave are mainly focused on emission of daily electrical equipments, which are normally called “low frequency electromagnetic waves”. In this work, a water pump with maximum magnetic field intensity of ca. 2300 mG was applied as emission source of the electromagnetic wave. Experimental measurements used various shielding materials with the major constituent iron (Fe) in the form of plate for studying shielding effect of electromagnetic wave. The studied parameters were different thicknesses and gaps of the plate. The results show that pure iron plate has the best effect for shielding the magnetic field and its transmission ratio of magnetic field is proportional to distance between the emission source and the shielding plate. Moreover, the shielding plate close to the emission source received better protection.

Electromagnetic Shielding and Absorption Properties of Fiber Reinforced Cementitious Composites

In order to investigate the electromagnetic shielding effectiveness （SE） and absorbing properties of fiber reinforced concrete, steel fiber, carbon fiber and synthetic polyvinyl alcohol （PVA） fiber reinforced concrete were researched. The results show that with the increase of fiber Volume fraction, the SE and trend of frequency change of corresponding fiber reinforced concrete are enhanced. When the volume content of steel fiber is 3%, the SE of concrete is above 50 dB and its frequency is above 1.8 GHz. Moreover, in the range of 8-18 GHz, steel fiber, carbon fiber and PVA fiber all can improve the microwave absorption properties of concrete. The concrete with 0.5% carbon fiber can achieve the best absorbing property, the minimum reflectivity is about -7 dB; while steel fiber optimal volume fraction is 2%. The reflectivity curve of PVA fiber reinforced concrete fluctuates with the frequency, and the minimum value of the reflectivity is below -10 dB. The results show that fiber reinforced concrete could be used as EMI（electromagnetic interference） prevention buildings by attenuating and reflecting electromagnetic wave energy.

Research on 3D Braided Nickel Plated Carbon Fiber/epoxy Resin Composites and Their Electromagnetic Protection Properties

To develop electromagnetic protection composites with integrated structure -function properties, the three-dimension (3D) braided nickel plated carbon fiber/epoxy resin (Ni-CF3D/EP) composites were prepared based on 3D five-directional braiding, unitary nickel plating and mold compression shaping. The electromagnetic protection properties of Ni-CF3D/EP composites including shielding effective- ness (SE) and reflection loss against plane electromagnetic wave, shielding properties against electromagnetic pulse (EMP) were investigated. The test results show that the novel composites have good electromagnetic protection properties in a wide frequency range of 14 kHz～18 GHz with SE of 42 dB～95 dB, the absorption bandwidth of –5 dB in 2 GHz～18 GHz can reach 10 GHz and the pulse peak SE against EMP is 43.7 dB which can reduce the electromagnetic energy greatly. Meanwhile, the mechanic properties were also investi- gated and the results indicate that the Ni-CF3D/EP composites can replace metal materials for loading-bearing structural applications because of their excellent mechanic properties.

Effects of Y and Zn additions on electrical conductivity and electromagnetic shielding effectiveness of Mg-Y-Zn alloys

Microstructure, electrical conductivity, and electromagnetic interference(EMI) shielding effectiveness(SE) of cast Mg-x Zn-y Y(x = 2–5, y = 1–10) alloys were systematically investigated to understand the effects of Zn and Y additions on electrical conductivity and electromagnetic shielding effectiveness of the alloys.Experimental results indicate that the electrical conductivity and SE of the Mg-x Zn-y Y alloys decrease with Y/Zn ratio. Electrical conductivity is the main factor that affects the electromagnetic shielding properties and the variation tendency of electromagnetic shielding properties of the Mg-x Zn-y Y alloys is consistent with conductivity. Valence of Y and Zn atoms, configuration of extranuclear electron and volumetric difference are main reasons for the variations in the electrical conductivity. A high density of second phase and the formation of semi-continuous network structure can also improve the SE value at high frequencies.

Preparation of Nylon MXD6/EG/CNTs Ternary Composites with Excellent Thermal Conductivity and Electromagnetic Interference Shielding Effectiveness

In this article, hybrid fillers with different dimensions, namely, 2-dimensional（2-D） expanded graphite（EG） and 1-dimensional（1-D） multi-walled carbon nanotubes（CNTs）, were added to aromatic nylon MXD6 matrix via melt-blending, to enhance its thermal and electrical conductivity as well as electromagnetic interference shielding effectiveness（EMI SE）. For ternary composites of MXD6/EG/CNTs, the electrical conductivity reaches up nine orders of magnitude higher compared to that of the neat MXD6 sample, which turned the polymer-based composites from an insulator to a conductor, and the thermal conductivity has been enhanced by 477% compared with that of neat MXD6 sample. Meanwhile, the EMI SE of ternary composite reaches ~50 d B at the overall filler loading of only 18 wt%. This work can provide guidance for the preparation of polymer composites with excellent thermal and electrical conductivity via using hybrid filler.

Effect of Alloying Element on Electromagnetic Interference Shielding Effectiveness of Binary Magnesium Alloys

The microstructure,electrical conductivity and electromagnetic interference shielding effectiveness of Mg-X(X=Al,Sn,Y and Gd)alloys in as-cast and solution states were systematically investigated in this study.The electrical conductivity and electromagnetic shielding capacity of binary magnesium alloys decrease linearly with alloying element content.The electromagnetic shielding effectiveness of the binary magnesium alloys with the same alloying element content is as follows:Mg-Gd<Mg-Sn<Mg-Y<Mg-Al.The main reason for the differences in electromagnetic interference shielding of the binary magnesium alloys is the change in conductivity,which is mainly affected by volumetric difference of solute atoms and magnesium atoms,solute atomic valence and configuration of extranuclear electron.

Achieving Excellent Electromagnetic Interference Shielding Effectiveness in High Rare Earth Mg-12Gd-3Y alloy via Nd Addition Combined with Hot Rolling and Aging

Achieving excellent electromagnetic interference(EMI)shielding effectiveness(SE)in high rare earth(RE)-content Mg alloys is currently a significant technical challenge.This work systematically investigated the effects of different Nd elements on the electrical conductivity and EMI SE of Mg-12Gd-3Y-xNd alloy by adding Nd elements to the high RE content Mg-12Gd-3Y alloy,followed by a combined process of hot rolling and aging(R-A).The results indicate that the addition of Nd elements leads to reduced solid solubility of Gd and Y,resulting in a large amount of precipitation.The Mg-12Gd-3Y-2.0Nd alloy has the optimum EMI SE after 63%R-A treatment,reaching 88-118 dB at 30-1500 MHz.The Mg-12Gd-3Y-xNd alloy has acicular and granular forms of the Mg5(Gd,Y,Nd)(abbreviated as Mg5RE)phase after R-A treatment.The granular Mg5RE phase gradually breaks up and refines into more minor scales with increasing rolling reduction and is diffusely distributed in the matrix.The acicular Mg5RE phase is densely arranged,with cross-distribution in some areas.The cross-distributed acicular Mg5RE phase,the delicate granular Mg5RE phase,and the denseβ′phase provide more interfaces for reflecting electromagnetic waves and increase the multiple reflection loss of incident electromagnetic waves.In addition,the Mg-12Gd-3Y-xNd alloy deflects most of the c-axis of the grains parallel to the normal direction(ND)as the rolling reduction increases,making the impedance difference between the plate surface and air larger.The increased impedance makes the material reflect more loss to incident electromagnetic waves.The combined use of these two leads to an excellent EMI SE of Mg-12Gd-3Y-xNd with high RE content after R-A treatment.

Electric Field Effects on Animals:Mechanism of Seismic Anomalous Animal Behaviors (SAABs)

Electric field effect on animals has been studied to investigate its relation with seismic anomalous animal behaviors(SAABs)in China.Freshwater eel,crucian carp,catfish,and soft-shelled turtle responded to the threshold electric field of 1-10 V/m,while duck,goose,cat,sheep,pig,dog,and chicken all responded to the ground electric field of about tens of V/m,depending on the species as well as on individuals.Most of the behaviors caused by electric field were similar to those reported as SAABs such as alignment,sudden movement,panic,and convulsion.The intensity of electric field due to a major earthquake would have been over these threshold values.Numerical estimation based on an electromagnetic model of a fault has been made to induce SAABs as electric shocks to pulsed electric fields in electro-physiology.The seismic electric signals(SES)intensity might be estimated from the observation of SAABs.

Preparation of CF/Ni-Fe/CNT/silicone layered rubber for aircraft sealing and electromagnetic interference shielding applications

To meet the needs of preventing information leakage in space engineering and military industry,an efficient method was introduced to obtain layered electromagnetic shielding sealing rubber.The carbon fiber,Ni-Fe coating,and Carbon Nano Tube(CNT)were combined by chemical plating and in-situ polymerization to obtain a lightweight(0.14 g/cm^(2))and thin(1 mm thick)Carbon fiber Fabric(CF)/Ni-Fe/CNT/silicone layered electromagnetic shielding composites.The layered material obtained by adjusting the electroless plating time exhibited a high Shielding Efficiency(SE)of 60.2–85.5 d B in the range of 0–4800 MHz,which can be used for aviation electromagnetic shielding.Carbon fibers and carbon nanotubes mainly attenuated electromagnetic waves through absorption loss,while the nickel-iron alloy coating through reflection loss interacted with the magnetic vector of incident Electro Magnetic(EM)radiation and magnetic dipoles,therefore,the EM Interference(EMI)shielding composite attenuated EM waves with the“absorptionreflection-absorption”cooperative interaction.Moreover,the flexible fabric substrate adhered with silicone rubber possessed a breaking elongation of 52.3%,which can be utilized as a good sealing material.Simultaneously,the outstanding exothermicity(67.2℃ under the applied voltage of 5 V)makes it possible to be applied in electric heating area.The electromagnetic shielding composites prepared in this paper have good potential in the fields of precision electronic equipment and aviation systems.

Effect of heat treatment temperature on microstructure and electromagnetic shielding properties of graphene/SiBCN composites

Three-dimensional(3D) graphene/SiBCN composites(GF/SiBCN) were prepared by depositing SiBCN ceramics in 3D graphene foam via the chemical vapor infiltration technique. The effect of the heat treatment temperature on the microstructure, phase composition, and electromagnetic properties of the GF/SiBCN composite was investigated. The SiBCN ceramics maintained an amorphous structure in the composite below 1400℃ above which the crystallinity of the free carbon phase gradually increased.While the Si3N4 and B4C phases started to crystallize at 1500℃ and their crystallinity increased with temperature, SiC was observed at 1700℃. The electromagnetic shielding effectiveness of GF/SiBCN increased with the heat treatment temperature.

Dielectric,Electromagnetic Interference Shielding and Absorption Properties of Si_3N_4-PyC Composite Ceramics

Pyrolytic carbon （PyC） was infiltrated into silicon nitride （Si3N4） ceramics by precursor infiltration and pyrolysis （PIP） of phenolic resin, and Ni nanoparticles were added into the phenolic resin to change the electric conductivity of Si3N4-PyC composite ceramics. Dielectric permittivity, electromagnetic interference （EMI） shielding and absorption properties of Si3N4-PyC composite ceramics were studied as a function of Ni content at 8.2-12.4 GHz （X-band）. When Ni nanoparticles were added into phenolic resin, the electric conductivity of the prepared composite ceramics decreased with increasing Ni content, which was attributed to the decrease of graphitization degree of PyC. The decrease in electric conductivity led to the decrease in both permittivity and EMI shielding effectiveness. Since too high permittivity is harmful to the impendence match and results in the strong reflection, the electromagnetic wave absorption property of Si3N4-PyC composite ceramics increases with increasing Ni content. When the content of Ni nanoparticles added into phenolic resin was 2 wt%, the composite ceramics possessed the lowest electric conductivity and displayed the most excellent absorption property with a minimum reflection loss as low as -28.9 dB.