As the proportion of composite materials used in aircraft continues to increase, the electromagnetic Shielding Effectiveness (SE) of these materials becomes a critical factor in the electromagnetic safety design of ai...As the proportion of composite materials used in aircraft continues to increase, the electromagnetic Shielding Effectiveness (SE) of these materials becomes a critical factor in the electromagnetic safety design of aircraft structures. The assessment of electromagnetic SE for Slotted Composite Structures(SCSs) is particularly challenging due to their complex geometries and there remains a lack of suitable models for accurately predicting the SE performance of these intricate configurations. To address this issue, this paper introduces SCS-Net, a Deep Neural Network (DNN) method designed to accurately predict the SE of SCS. This method considers the impacts of various structural parameters, material properties and incident wave parameters on the SE of SCSs. In order to better model the SCS, an improved Nicolson-Ross-Weir (NRW) method is introduced in this paper to provide an equivalent flat structure for the SCS and to calculate the electromagnetic parameters of the equivalent structure. Additionally, the prediction of SE via DNNs is limited by insufficient test data, which hinders support for large-sample training. To address the issue of limited measured data, this paper develops a Measurement-Computation Fusion (MCF) dataset construction method. The predictions based on the simulation results show that the proposed method maintains an error of less than 0.07 dB within the 8–10 GHz frequency range. Furthermore, a new loss function based on the weighted L1-norm is established to improve the prediction accuracy for these parameters. Compared with traditional loss functions, the new loss function reduces the maximum prediction error for equivalent electromagnetic parameters by 47%. This method significantly improves the prediction accuracy of SCS-Net for measured data, with a maximum improvement of 23.88%. These findings demonstrate that the proposed method enables precise SE prediction and design for composite structures while reducing the number of test samples needed.展开更多
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 ana...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.展开更多
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...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.展开更多
Shielding effect and emission criterion of a screw dislocation near an interracial blunt crack are dealt with in this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex...Shielding effect and emission criterion of a screw dislocation near an interracial blunt crack are dealt with in this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentials and stress fields due to a screw dislocation located near the interracial blunt crack. The stress intensity factor on the crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of the orientation of the dislocation and the morphology of the blunt crack as well as the material elastic dissimilarity on the shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations can reduce the stress intensity factor of the interfacial blunt crack tip （shielding effect）. The shielding effect increases with the increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuth angle. The critical loads at infinity for dislocation emission increases with the increase of emission angle and curvature radius of blunt crack tip, and the most probable angle for screw dislocation emission is zero. The present solutions contain previous results as special cases.展开更多
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...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.展开更多
In 1992,E.E.Podkletnov and R.Nieminen found that under certain conditions,ceramic superconductor with composite structure reveals weak shielding properties against gravitational force.In classical Newton's theory ...In 1992,E.E.Podkletnov and R.Nieminen found that under certain conditions,ceramic superconductor with composite structure reveals weak shielding properties against gravitational force.In classical Newton's theory of gravity and even in Einstein's general theory of gravity,there are no grounds of gravitational shielding effects.But in quantum gauge theory of gravity,the gravitational shielding effects can be explained in a simple and natural way.In quantum gauge theory of gravity,gravitational gauge interactions of complex scalar field can be formulated based on gauge principle.After spontaneous symmetry breaking,if the vacuum of the complex scalar field is not stable and uniform,there will be a mass term of gravitational gauge field.When gravitational gauge field propagates in this unstable vacuum of the complex scalar field,it will decays exponentially,which is the nature of gravitational shielding effects.The mechanism of gravitational shielding effects is studied in this paper,and some main properties of gravitational shielding effects are discussed.展开更多
Shielding effect and emission criterion of a screw dislocation near an interracial crisscross crack are dealt within this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for com...Shielding effect and emission criterion of a screw dislocation near an interracial crisscross crack are dealt within this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentialsand stress fields due to a screw dislocation located near the interracial crisscross crack. The stress intensity factor onthe crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of theorientation of the dislocation and the morphology of the crisscross crack as well as the material elastic dissimilarity onthe shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations canreduce the stress intensity factor of the interracial crisscross crack tip (shielding effect). The shielding effect increases withthe increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuthangle and the distance between the dislocation and the crack tip. The critical loads at infinity for dislocation emissionincreases with the increase of emission angle and the vertical length of the crisscross crack, and the most probable anglefor screw dislocation emission is zero. The present solutions contain previous results as special cases.展开更多
The shielding effect of the front pile-row on the ice force acting on the back pile-row is studied by ice force model tests. In the tests, the front pile-row is designed to model jacket legs and the back pile-row to m...The shielding effect of the front pile-row on the ice force acting on the back pile-row is studied by ice force model tests. In the tests, the front pile-row is designed to model jacket legs and the back pile-row to model the water resisting pipe-phalanx within the jacket. The shielding factor for ice force corresponding to different conditions are given in this paper. The research indicates that there are many factors, including the longitudinal and lateral spacing between the front and back pile-row, ice attacking angle and the ratio of pile diameter to ice thickness, that influence the shielding effect on ice force.展开更多
The model of a screw dislocation near a semi-infinite wedge crack tip inside a nano-circular inclusion is proposed to investigate the shielding effect of nano inclusions acting on cracks. Utilizing the complex functio...The model of a screw dislocation near a semi-infinite wedge crack tip inside a nano-circular inclusion is proposed to investigate the shielding effect of nano inclusions acting on cracks. Utilizing the complex function method, the closed-form solutions of the stress fields in the matrix and the inclusion region are derived. The stress intensity factor, the image force, as well as the critical loads for dislocation emission are discussed in detail. The results show that the nano inclusion not only enhances the shielding effect exerted by the dislocation, but also provides a shielding effect itself. Moreover, dislocations may be trapped in the nano inclusion even if the matrix is softer than the inclusion. This helps the dislocation shield crack, and reduces the dislocation density within the matrix.展开更多
Two tigogenyl glycosides containing N-acetylglucosamine were synthesized. Their structures were confirmed by ^1H and ^13C NMR spectra. The shielding effect caused by benzoyl groups was elucidated by ^1H NMR, COSY, HSQ...Two tigogenyl glycosides containing N-acetylglucosamine were synthesized. Their structures were confirmed by ^1H and ^13C NMR spectra. The shielding effect caused by benzoyl groups was elucidated by ^1H NMR, COSY, HSQC, HMBC spectroscopy.展开更多
Magnetic shielding is very important in the design of a high-power dc comparator. This paper addressed the application of magnetic circuit method to calculate the magnetic shielding effectiveness of high-power dc comp...Magnetic shielding is very important in the design of a high-power dc comparator. This paper addressed the application of magnetic circuit method to calculate the magnetic shielding effectiveness of high-power dc comparators when an external radial magnetic field is added. The mathematical relationship between the magnetic shielding effectiveness and the parameters of the magnetic shielding body were obtained. To verify the validity of the calculation method, we developped a procedure to measure the magnetic shielding effectiveness of the magnetic body by measuring the induction voltage of the detection winding instead of the magnetic intensity at a point in the magnetic shielding body, making the manipulation much easier. The result calculated with the magnetic circuit method turns out to be closer to the measured one compared with that calculated with a conventional algorithm proposed by Ren, suggesting that the magnetic circuit method is an applicable tool for estimating the toroidal cavity magnetic shielding effectiveness of a heavy current comparator when a radial magnetic field is added.展开更多
There are magnetic interference problems in the applications of DC current comparator. Analysis on the magnetic effectiveness which is applied by the external magnetic field is introduced in this paper. The effectiven...There are magnetic interference problems in the applications of DC current comparator. Analysis on the magnetic effectiveness which is applied by the external magnetic field is introduced in this paper. The effectiveness is proved by the actual results which are compared with the magnetic- circuit method and the finite element method. In addition, the reference comment is given which can be used in the practical work of DC current comparator shield design.展开更多
The paper presents the synthesis and characterization of carbon black/silicone dioxide hybrid fillers obtained by an impregnation technology. The electromagnetic interference shielding effectiveness of the composites ...The paper presents the synthesis and characterization of carbon black/silicone dioxide hybrid fillers obtained by an impregnation technology. The electromagnetic interference shielding effectiveness of the composites filled with carbon black/silicone dioxide hybrid fillers was measured in wide frequency range of 1 - 12 GHz. The dc and ac electrical conductivity of composites also have been investigated. The relationship between electrical (dc and ac) conductivity and shielding effectiveness was analyzed. A positive correlation was found between the absorptive shielding effectiveness and ac conductivity for composites comprising conductive carbon black/silica filler, when the filler loading is above the percolation threshold.展开更多
The impact of Y content on the microstructure,mechanical properties,and electromagnetic interference shielding effectiveness(EMI SE)of the Mg-6Zn-xY-1La-0.5Zr alloy was investigated.After the extrusion treatment of Mg...The impact of Y content on the microstructure,mechanical properties,and electromagnetic interference shielding effectiveness(EMI SE)of the Mg-6Zn-xY-1La-0.5Zr alloy was investigated.After the extrusion treatment of Mg-6Zn-xY-1La-0.5Zr alloy,the large grains that did not experience dynamic recrystallization were elongated along the extrusion direction,and the small-sized dynamic recrystallized grains were distributed around the large grains.The Mg-6Zn-1Y-1La-0.5Zr alloy demonstrated a favorable balance between strength and plasticity,exhibiting ultimate tensile strength,yield strength,and elongation values of 332.3 MPa,267.3 MPa,and 16.2%,respectively.Moreover,the EMI SE within the frequency range of 30-1500 MHz changes from 79 to 110 dB,aligning with the electromagnetic shielding requirements of many high-strength applications.展开更多
In order to prepare the shielding fabrics with high efficiency of power frequency(PF)shielding and excellent electrical conductivity,different ratios of aramid/stainless steel fiber blended yarns were used to weave th...In order to prepare the shielding fabrics with high efficiency of power frequency(PF)shielding and excellent electrical conductivity,different ratios of aramid/stainless steel fiber blended yarns were used to weave the shielding fabrics with different specifications.The fabric structure,fabric areal density,number of fabric layers,embedding ratio of copper-clad wires wrapped aramid yarns(denoted as CCWWA)and embedding direction were designed,and a total of 34 different types of shielding fabrics were woven for testing.The experiments were mainly conducted to study the influence mechanism of various factors on the PF shielding effectiveness by testing the electrical conductivity and PF shielding effectiveness of the fabrics.The research results indicate that the PF shielding effectiveness improves with increasing fabric areal density and metal fiber content.The fabrics embedded with CCWWA,particularly those with bidirectional embedding,exhibit a significant enhancement in the PF shielding effectiveness,showing an increase of 8-20 dB compared to the fabrics without CCWWA.The PF shielding effectiveness varies across different fabric structures,with plain weave fabrics demonstrating the superior PF shielding effectiveness due to their compact structure.Non-conductive base fabric has minimal impact on the PF shielding effectiveness.As the number of fabric layers increases,the PF shielding effectiveness initially improves but then declines,peaking with double-layer fabrics.展开更多
Achieving the spin-exchange relaxation-free(SERF)state in atomic comagnetometers(ACMs)necessitates a stable and weak magnetic environment.This paper presents the design of a miniaturized permalloy magnetic shielding s...Achieving the spin-exchange relaxation-free(SERF)state in atomic comagnetometers(ACMs)necessitates a stable and weak magnetic environment.This paper presents the design of a miniaturized permalloy magnetic shielding spherical shell(MSSS)with minimal apertures,tailored to meet these requirements.By employing a combination of analytical solutions and finite element analysis(FEA),we achieved superior magnetic shielding while maintaining a compact form factor.The analytical solution for the shielding factor indicated that a four-layer permalloy sphere shell with optimized air gaps was necessary.A numerical analysis model of the MSSS was developed and validated using COMSOL software,confirming the suitability of the air gaps.The size,shape,and orientation of the openings in the perforated sphere shell were meticulously designed and optimized to minimize residual magnetism.The optimal structure was fabricated,resulting in triaxial shielding factors of 47619,52631,and 21739,meeting the anticipated requirements.A comparison of simulation results with experimental tests demonstrated the efficacy of the design methodology.This study has significant implications for ultrasensitive magnetic field detection devices requiring weak magnetic field environments,such as atomic gyroscopes,magnetometers,atomic interferometers,and atomic clocks.展开更多
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 t...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.展开更多
The Shielding coefficient of superconductor in the shape of the spherical shell is derived on the basis of Maxwell's equations and London's two-liquid model. Some cases of superconductor shielding have also ...The Shielding coefficient of superconductor in the shape of the spherical shell is derived on the basis of Maxwell's equations and London's two-liquid model. Some cases of superconductor shielding have also been discussed in this paper.展开更多
fields such as lightning strike susceptibility,electromagnetic energy from radar,airborne radio frequency transmitter.To provide high-intensity radiated field protection(HIRFP)for the electric and electronic aircraft ...fields such as lightning strike susceptibility,electromagnetic energy from radar,airborne radio frequency transmitter.To provide high-intensity radiated field protection(HIRFP)for the electric and electronic aircraft system and defied the EMI effect on it,metal matrix composite was conquered.To provide the dynamic everincreasing requirement of industries,it is necessary that Al6061 metal matrix composite assisted with AL2O3 and fly ash is used to construct the aircraft to provide HIRFP.The thickness of the material can be maintained as low as possible to use it as a coating material for the aircraft surface.X-band for oblique incidence is used to measure electromagnetic and mechanical safeguarding properties of composites.Design/methodology/approach-Day by day,the applications of aerospace are becoming digital and automated.Proper shielding techniques are required to operate digital electronic devices without electromagnetic interference.It leads to a rapid rise in temperature,thermal ablation,delamination,and adverse effects on the electric and electronic aircraft system.Fly ash,a metal matrix material composite AL6061 with different percentages of reinforcement of Al_(2)O_(3),was contemplated and experimented with for mechanical properties like tensile strength,density and hardness.Findings-The obtained results compared with adjusted values and an improvement of 0.19,0.18,0.14 g/cm3 for density of MMC-1,MMC-2,MMC-3.31,11 MPa for tensile strength of MMC-1,MMC-2.24,27,23 BHN for hardness of MMC-1,MMC-2,MMC-3.With regard to the shielding effectiveness the results compared with adjusted values and obtained 11.36,14.56,19.47 dB better value than it.According to the above results,fabricated MMC’s provide superior results for a defined application like HIRFP(Surface material of aircraft).Practical implications-It can be used to protect electronic devices under a high-intensity radiated field,mainly in aircraft design to protect from lightning effect.Originality/value-For a better approximation of the signal toward the practical case,the oblique incidence was considered with a different combination of Al_(2)O_(3)and fly ash,reinforced to pure AL6061 to get better shielding and mechanical properties.展开更多
New shielding material has become an alternative to traditional metal to shield boxes from electromagnetic interferences. This article introduces the theory of transmission line method to study the shield boxes made o...New shielding material has become an alternative to traditional metal to shield boxes from electromagnetic interferences. This article introduces the theory of transmission line method to study the shield boxes made of a new sort of material, and then expands the fundamental formulas to deal with the cases of multiple holes and polarization with arbitrary angle. By means of genetic algorithms with the aid of a three dimensional simulation tool, the damping of electromagnetic resonances in enclosures is researched. The computation indicates that under resonant frequency, electromagnetic resonance results in low, even negative shielding coefficient; whereas, for the same areas, shielding effectiveness of a single hole is worse than that of multiple holes. Shielding coefficient varies when polarization angle increases, and the coupled field through the rectangular aperture with the long side parallel to the thin wire is much weaker than that with the long side vertical to the thin wire. By using the metallic-loss dielectric layer of optimized calculation on the internal surface of the cavity, the best result of resonance suppression has been realized with the same thickness of coating. Finally, according to the calculation result, suggestions for shielding are proposed.展开更多
基金supported by the National Natural Science Foundation of China(Nos.62101020 and 62141405)the Special Scientific Research Project of Civil Aircraft,China(No.MJZ5-2N22).
文摘As the proportion of composite materials used in aircraft continues to increase, the electromagnetic Shielding Effectiveness (SE) of these materials becomes a critical factor in the electromagnetic safety design of aircraft structures. The assessment of electromagnetic SE for Slotted Composite Structures(SCSs) is particularly challenging due to their complex geometries and there remains a lack of suitable models for accurately predicting the SE performance of these intricate configurations. To address this issue, this paper introduces SCS-Net, a Deep Neural Network (DNN) method designed to accurately predict the SE of SCS. This method considers the impacts of various structural parameters, material properties and incident wave parameters on the SE of SCSs. In order to better model the SCS, an improved Nicolson-Ross-Weir (NRW) method is introduced in this paper to provide an equivalent flat structure for the SCS and to calculate the electromagnetic parameters of the equivalent structure. Additionally, the prediction of SE via DNNs is limited by insufficient test data, which hinders support for large-sample training. To address the issue of limited measured data, this paper develops a Measurement-Computation Fusion (MCF) dataset construction method. The predictions based on the simulation results show that the proposed method maintains an error of less than 0.07 dB within the 8–10 GHz frequency range. Furthermore, a new loss function based on the weighted L1-norm is established to improve the prediction accuracy for these parameters. Compared with traditional loss functions, the new loss function reduces the maximum prediction error for equivalent electromagnetic parameters by 47%. This method significantly improves the prediction accuracy of SCS-Net for measured data, with a maximum improvement of 23.88%. These findings demonstrate that the proposed method enables precise SE prediction and design for composite structures while reducing the number of test samples needed.
基金Project supported by Anhui Province Natural Science Foundation (050440603)
文摘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.
基金financially supported by the National Key R&D Program of China(2021YFB3701100)the National Natural Science Foundation of China(52225101 and 52171103)the Fundamental Research Funds for the Central Universities(2020CDJDPT001).
文摘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.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10872065 and 50801025)
文摘Shielding effect and emission criterion of a screw dislocation near an interracial blunt crack are dealt with in this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentials and stress fields due to a screw dislocation located near the interracial blunt crack. The stress intensity factor on the crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of the orientation of the dislocation and the morphology of the blunt crack as well as the material elastic dissimilarity on the shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations can reduce the stress intensity factor of the interfacial blunt crack tip （shielding effect）. The shielding effect increases with the increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuth angle. The critical loads at infinity for dislocation emission increases with the increase of emission angle and curvature radius of blunt crack tip, and the most probable angle for screw dislocation emission is zero. The present solutions contain previous results as special cases.
基金This study is supported by Shaanxi Provincial Laboratory of Functional Textiles and Academy Laboratory of Xi’an University of Engineer-ing Science and Technology in Xi’an city ,P.R.Chian
文摘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.
文摘In 1992,E.E.Podkletnov and R.Nieminen found that under certain conditions,ceramic superconductor with composite structure reveals weak shielding properties against gravitational force.In classical Newton's theory of gravity and even in Einstein's general theory of gravity,there are no grounds of gravitational shielding effects.But in quantum gauge theory of gravity,the gravitational shielding effects can be explained in a simple and natural way.In quantum gauge theory of gravity,gravitational gauge interactions of complex scalar field can be formulated based on gauge principle.After spontaneous symmetry breaking,if the vacuum of the complex scalar field is not stable and uniform,there will be a mass term of gravitational gauge field.When gravitational gauge field propagates in this unstable vacuum of the complex scalar field,it will decays exponentially,which is the nature of gravitational shielding effects.The mechanism of gravitational shielding effects is studied in this paper,and some main properties of gravitational shielding effects are discussed.
基金Supported by the National Natural Science Foundation of China under Grant Nos. 10872065, 50801025Hunan Provincial Innovation Foundation for Postgraduate under Grant No. CX2009B067
文摘Shielding effect and emission criterion of a screw dislocation near an interracial crisscross crack are dealt within this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentialsand stress fields due to a screw dislocation located near the interracial crisscross crack. The stress intensity factor onthe crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of theorientation of the dislocation and the morphology of the crisscross crack as well as the material elastic dissimilarity onthe shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations canreduce the stress intensity factor of the interracial crisscross crack tip (shielding effect). The shielding effect increases withthe increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuthangle and the distance between the dislocation and the crack tip. The critical loads at infinity for dislocation emissionincreases with the increase of emission angle and the vertical length of the crisscross crack, and the most probable anglefor screw dislocation emission is zero. The present solutions contain previous results as special cases.
文摘The shielding effect of the front pile-row on the ice force acting on the back pile-row is studied by ice force model tests. In the tests, the front pile-row is designed to model jacket legs and the back pile-row to model the water resisting pipe-phalanx within the jacket. The shielding factor for ice force corresponding to different conditions are given in this paper. The research indicates that there are many factors, including the longitudinal and lateral spacing between the front and back pile-row, ice attacking angle and the ratio of pile diameter to ice thickness, that influence the shielding effect on ice force.
基金Project supported by the Postdoctoral Research Funds of Jiangsu Province, China (Grant No. 1002008B)the China Postdoctoral Science Foundation (Grant No. 20110491416)
文摘The model of a screw dislocation near a semi-infinite wedge crack tip inside a nano-circular inclusion is proposed to investigate the shielding effect of nano inclusions acting on cracks. Utilizing the complex function method, the closed-form solutions of the stress fields in the matrix and the inclusion region are derived. The stress intensity factor, the image force, as well as the critical loads for dislocation emission are discussed in detail. The results show that the nano inclusion not only enhances the shielding effect exerted by the dislocation, but also provides a shielding effect itself. Moreover, dislocations may be trapped in the nano inclusion even if the matrix is softer than the inclusion. This helps the dislocation shield crack, and reduces the dislocation density within the matrix.
基金the National Natural Science Foundation of China （No. 20372085）
文摘Two tigogenyl glycosides containing N-acetylglucosamine were synthesized. Their structures were confirmed by ^1H and ^13C NMR spectra. The shielding effect caused by benzoyl groups was elucidated by ^1H NMR, COSY, HSQC, HMBC spectroscopy.
基金Funded by the Natural Science Foundation of China under the grant number 50277018.
文摘Magnetic shielding is very important in the design of a high-power dc comparator. This paper addressed the application of magnetic circuit method to calculate the magnetic shielding effectiveness of high-power dc comparators when an external radial magnetic field is added. The mathematical relationship between the magnetic shielding effectiveness and the parameters of the magnetic shielding body were obtained. To verify the validity of the calculation method, we developped a procedure to measure the magnetic shielding effectiveness of the magnetic body by measuring the induction voltage of the detection winding instead of the magnetic intensity at a point in the magnetic shielding body, making the manipulation much easier. The result calculated with the magnetic circuit method turns out to be closer to the measured one compared with that calculated with a conventional algorithm proposed by Ren, suggesting that the magnetic circuit method is an applicable tool for estimating the toroidal cavity magnetic shielding effectiveness of a heavy current comparator when a radial magnetic field is added.
文摘There are magnetic interference problems in the applications of DC current comparator. Analysis on the magnetic effectiveness which is applied by the external magnetic field is introduced in this paper. The effectiveness is proved by the actual results which are compared with the magnetic- circuit method and the finite element method. In addition, the reference comment is given which can be used in the practical work of DC current comparator shield design.
文摘The paper presents the synthesis and characterization of carbon black/silicone dioxide hybrid fillers obtained by an impregnation technology. The electromagnetic interference shielding effectiveness of the composites filled with carbon black/silicone dioxide hybrid fillers was measured in wide frequency range of 1 - 12 GHz. The dc and ac electrical conductivity of composites also have been investigated. The relationship between electrical (dc and ac) conductivity and shielding effectiveness was analyzed. A positive correlation was found between the absorptive shielding effectiveness and ac conductivity for composites comprising conductive carbon black/silica filler, when the filler loading is above the percolation threshold.
基金supported from the National Key R&D Program of China(No.2021YFB3701100)the National Natural Science Foundation of China(No.52225101)+1 种基金the Fundamental Research Funds for the Central Universities of China(Nos.2023CDJYXTD-002,2020CDJDPT001)the Graduate Research and Innovation Foundation of Chongqing,China(No.CYB23037).
文摘The impact of Y content on the microstructure,mechanical properties,and electromagnetic interference shielding effectiveness(EMI SE)of the Mg-6Zn-xY-1La-0.5Zr alloy was investigated.After the extrusion treatment of Mg-6Zn-xY-1La-0.5Zr alloy,the large grains that did not experience dynamic recrystallization were elongated along the extrusion direction,and the small-sized dynamic recrystallized grains were distributed around the large grains.The Mg-6Zn-1Y-1La-0.5Zr alloy demonstrated a favorable balance between strength and plasticity,exhibiting ultimate tensile strength,yield strength,and elongation values of 332.3 MPa,267.3 MPa,and 16.2%,respectively.Moreover,the EMI SE within the frequency range of 30-1500 MHz changes from 79 to 110 dB,aligning with the electromagnetic shielding requirements of many high-strength applications.
文摘In order to prepare the shielding fabrics with high efficiency of power frequency(PF)shielding and excellent electrical conductivity,different ratios of aramid/stainless steel fiber blended yarns were used to weave the shielding fabrics with different specifications.The fabric structure,fabric areal density,number of fabric layers,embedding ratio of copper-clad wires wrapped aramid yarns(denoted as CCWWA)and embedding direction were designed,and a total of 34 different types of shielding fabrics were woven for testing.The experiments were mainly conducted to study the influence mechanism of various factors on the PF shielding effectiveness by testing the electrical conductivity and PF shielding effectiveness of the fabrics.The research results indicate that the PF shielding effectiveness improves with increasing fabric areal density and metal fiber content.The fabrics embedded with CCWWA,particularly those with bidirectional embedding,exhibit a significant enhancement in the PF shielding effectiveness,showing an increase of 8-20 dB compared to the fabrics without CCWWA.The PF shielding effectiveness varies across different fabric structures,with plain weave fabrics demonstrating the superior PF shielding effectiveness due to their compact structure.Non-conductive base fabric has minimal impact on the PF shielding effectiveness.As the number of fabric layers increases,the PF shielding effectiveness initially improves but then declines,peaking with double-layer fabrics.
基金supported by Hefei National Laboratory,Innovation Program for Quantum Science and Technology(Grant Nos.2021ZD0300500 and 2021ZD0300503).
文摘Achieving the spin-exchange relaxation-free(SERF)state in atomic comagnetometers(ACMs)necessitates a stable and weak magnetic environment.This paper presents the design of a miniaturized permalloy magnetic shielding spherical shell(MSSS)with minimal apertures,tailored to meet these requirements.By employing a combination of analytical solutions and finite element analysis(FEA),we achieved superior magnetic shielding while maintaining a compact form factor.The analytical solution for the shielding factor indicated that a four-layer permalloy sphere shell with optimized air gaps was necessary.A numerical analysis model of the MSSS was developed and validated using COMSOL software,confirming the suitability of the air gaps.The size,shape,and orientation of the openings in the perforated sphere shell were meticulously designed and optimized to minimize residual magnetism.The optimal structure was fabricated,resulting in triaxial shielding factors of 47619,52631,and 21739,meeting the anticipated requirements.A comparison of simulation results with experimental tests demonstrated the efficacy of the design methodology.This study has significant implications for ultrasensitive magnetic field detection devices requiring weak magnetic field environments,such as atomic gyroscopes,magnetometers,atomic interferometers,and atomic clocks.
基金supported by the National Key Research and Development Program of China (No. 2018YFB1106600)the Chinese National Foundation for Natural Sciences under Contracts (No. 51672217, 51572224)the Fundamental Research Funds for the Central Universities (Grant no. 3102019ghxm014)
文摘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.
文摘The Shielding coefficient of superconductor in the shape of the spherical shell is derived on the basis of Maxwell's equations and London's two-liquid model. Some cases of superconductor shielding have also been discussed in this paper.
文摘fields such as lightning strike susceptibility,electromagnetic energy from radar,airborne radio frequency transmitter.To provide high-intensity radiated field protection(HIRFP)for the electric and electronic aircraft system and defied the EMI effect on it,metal matrix composite was conquered.To provide the dynamic everincreasing requirement of industries,it is necessary that Al6061 metal matrix composite assisted with AL2O3 and fly ash is used to construct the aircraft to provide HIRFP.The thickness of the material can be maintained as low as possible to use it as a coating material for the aircraft surface.X-band for oblique incidence is used to measure electromagnetic and mechanical safeguarding properties of composites.Design/methodology/approach-Day by day,the applications of aerospace are becoming digital and automated.Proper shielding techniques are required to operate digital electronic devices without electromagnetic interference.It leads to a rapid rise in temperature,thermal ablation,delamination,and adverse effects on the electric and electronic aircraft system.Fly ash,a metal matrix material composite AL6061 with different percentages of reinforcement of Al_(2)O_(3),was contemplated and experimented with for mechanical properties like tensile strength,density and hardness.Findings-The obtained results compared with adjusted values and an improvement of 0.19,0.18,0.14 g/cm3 for density of MMC-1,MMC-2,MMC-3.31,11 MPa for tensile strength of MMC-1,MMC-2.24,27,23 BHN for hardness of MMC-1,MMC-2,MMC-3.With regard to the shielding effectiveness the results compared with adjusted values and obtained 11.36,14.56,19.47 dB better value than it.According to the above results,fabricated MMC’s provide superior results for a defined application like HIRFP(Surface material of aircraft).Practical implications-It can be used to protect electronic devices under a high-intensity radiated field,mainly in aircraft design to protect from lightning effect.Originality/value-For a better approximation of the signal toward the practical case,the oblique incidence was considered with a different combination of Al_(2)O_(3)and fly ash,reinforced to pure AL6061 to get better shielding and mechanical properties.
基金the National Natural Science Foundation of China (50237040)
文摘New shielding material has become an alternative to traditional metal to shield boxes from electromagnetic interferences. This article introduces the theory of transmission line method to study the shield boxes made of a new sort of material, and then expands the fundamental formulas to deal with the cases of multiple holes and polarization with arbitrary angle. By means of genetic algorithms with the aid of a three dimensional simulation tool, the damping of electromagnetic resonances in enclosures is researched. The computation indicates that under resonant frequency, electromagnetic resonance results in low, even negative shielding coefficient; whereas, for the same areas, shielding effectiveness of a single hole is worse than that of multiple holes. Shielding coefficient varies when polarization angle increases, and the coupled field through the rectangular aperture with the long side parallel to the thin wire is much weaker than that with the long side vertical to the thin wire. By using the metallic-loss dielectric layer of optimized calculation on the internal surface of the cavity, the best result of resonance suppression has been realized with the same thickness of coating. Finally, according to the calculation result, suggestions for shielding are proposed.
