Ba2ZnxCo2-xFe12O22 hexaferrites with x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0 were prepared by citrate sol-gel process. The complex dielectric constant and complex permeability of hexaferrites were studied as functions of ...Ba2ZnxCo2-xFe12O22 hexaferrites with x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0 were prepared by citrate sol-gel process. The complex dielectric constant and complex permeability of hexaferrites were studied as functions of the measuring frequency, composition and sintering temperature in the range 100 MHz similar to 6 GHz. The natural resonance phenomenon is observed in mu' spectrum for all Y-type hexaferrites, which resonance frequency is dependent on zinc content and firing temperature. The natural resonance frequencies Of Co2Y hexaferrite were calculated, which is in agreement with the measuring results. The reflection loss of those ferrites is measuring frequency as well as absorber thickness dependent, and the higher the frequency and the thickness are, the higher the reflection loss is.展开更多
The paper presents a comparative study on the electric, dielectric and microwave properties of natural rubber based composites comprising dual phase fillers prepared from furnace carbon black or conductive carbon blac...The paper presents a comparative study on the electric, dielectric and microwave properties of natural rubber based composites comprising dual phase fillers prepared from furnace carbon black or conductive carbon black with a different amount of silica. It has been established that, the specifics of the carbon phase have a marked strong effect upon the properties mentioned above. The interpenetration of the two filler phases and the grade of isolation of the conductive carbon phase by the dielectric one depend on the ratio between them. On the other hand, that leads to a change in all properties of the studied composites, which allows tailoring those characteristics.展开更多
A single layer of CoFeB and a multilayer of CoFeB MgO films are prepared by means of DC/RF magnetron sputter deposition. The excellent microwave properties and high electrical resistivity are simultaneously achieved i...A single layer of CoFeB and a multilayer of CoFeB MgO films are prepared by means of DC/RF magnetron sputter deposition. The excellent microwave properties and high electrical resistivity are simultaneously achieved in the discontinuous multilayer structure of [Co44Fe44B12（0.7nm）/MgO（0.4nm）]40 film. This film has a high permeability （μ′） （larger than 100 below 2.1 GHz）, a high magnetic loss （μ″） （larger than 100 in a range from 1.5 to 3.3GHz）, a resistivity of 3.3 × 10^3μΩ. cm, a saturation magnetization of 1.2 T, and an in-plane uniaxial anisotropy field of 5.5 kA/m. The microstructure and the surface topography of the film are also analysed. The relatively large surface roughness for the discontinuous film is responsible for the wide frequency band of magnetic loss. The magnetic loss and the high resistivity indicate that the discontinuous CoFeB MgO multilayer film has potential applications in microwave absorbers and electromagnetic interference （EMI） shielding materials in a GHz frequency range.展开更多
BaZnzCo2-zFe16O27/SiO2 microcrystalline glass ceramics with Z=0.0, 0.5, 0.8 and 1.1 were prepared at temperature 1200℃ for 5h by citrate sol-gel process. The complex dielectric constant and complex permeability of Ba...BaZnzCo2-zFe16O27/SiO2 microcrystalline glass ceramics with Z=0.0, 0.5, 0.8 and 1.1 were prepared at temperature 1200℃ for 5h by citrate sol-gel process. The complex dielectric constant and complex permeability of BaZnzCo2-zFe16 O27/SiO2-paraffin wax composites had been measured. Both the complex dielectric constant and dielectric loss exhibit almost no variation with frequency in 0.1-6.0GHz. The real part of permeability decreases with increasing frequency for all samples, and the imaginary part of permeability exhibits a clear resonance peak at 1.44GHz for Co2 W/SiO2, 1.32GHz for Zn0.5Co1.5 W/SiO2, 1.20GHz for Zn0.8Co1.2W/SiO2, and 1.08GHz for Zn1.1 Co0.9 W/SiO2. It is also showed that the content of zinc has a close effect on the magnetic properties of BaZnzCo2-zFe16O27/SiO2 microcrystalline glass ceramics, the greater the zinc content, the higher the values of imaginary part of permeability and magnetic loss.展开更多
In order to improve the absorbing properties of M- type barium ferrite absorbing materials, M-type barium ferrite/graphene oxide composites with different graphene oxide contents were synthesized by the sol-gel autoco...In order to improve the absorbing properties of M- type barium ferrite absorbing materials, M-type barium ferrite/graphene oxide composites with different graphene oxide contents were synthesized by the sol-gel autocombustion method. X-ray diffraction （XRD）, a scanning electronic microscopy （ SEM ）, a physical properties measurement system （PPMS-9）, and a vector network analyzer were used to analyze their structure, surface morphology, magnetic and absorbing properties, respectively. The results show that the absorbing band of the composite absorbing material is widened and the absorbing strength is increased compared with the pure M-type barium ferrite. The sample with the content of doped graphene oxide of 3% has the minimum reflectivity at 10 to 18 GHz frequencies. Hence, the doped graphene oxide effectively improves the absorbing properties of M-type barium ferrite.展开更多
Coaxially dielectric samples consisting of different packing ratios of glass-covered Fe73.5Si13.5B9Nb3Cu1 amorphous wires embedded in a paraffin wax matrix were fabricated, and the influence of short-wire packing rati...Coaxially dielectric samples consisting of different packing ratios of glass-covered Fe73.5Si13.5B9Nb3Cu1 amorphous wires embedded in a paraffin wax matrix were fabricated, and the influence of short-wire packing ratio (3%-9% in mass fraction) and thickness (1-7 mm) on the microwave absorption properties was systematically investigated in microwave frequency range of 2-18 GHz. X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and scalar network analyzer (SNA) were used for characterizing microstructure and evaluating microwave absorption properties. Experimental results show the significant frequency (6-18 GHz) dependence of the complex relative permeability and permittivity. The reflection loss (RL) with different thickness and short-wire packing ratio reveals that the composite sample containing 7% exhibits better microwave absorption behavior with its minimum value of RL reaching-34 dB in thickness of 3 mm at 14 GHz. Therefore, it is significantly useful to develop microwire-dielectric materials with much wider absorption band for microwave absorption applications.展开更多
La-doped Sr-hexaferrite（Sr（1-x）LaxFe（12）O（19））（x=0.05,0.10,0.15,0.20） nanopowders with particle size ranging from 80 to 110 nm were successfully synthesized by sol-gel auto-combustion. The phase formation te...La-doped Sr-hexaferrite（Sr（1-x）LaxFe（12）O（19））（x=0.05,0.10,0.15,0.20） nanopowders with particle size ranging from 80 to 110 nm were successfully synthesized by sol-gel auto-combustion. The phase formation temperature increases, while the particle size decreases as the Ladoping content goes up. The partial substitution of Sr^（2＋） by La^（3＋） results in the suppression effects on the growth-up of the crystallites and the enhancement of the electron hopping between Fe^（3＋） with different valences, which leads to the improvement in the dielectric loss and magnetic loss.Therefore, both the microwave absorbing abilities and absorbing frequency ranges are tuned by La-doping. The synthesized Sr-hexaferrite nanopowders with doping element content of 0.10 demonstrate the fine broad microwave absorbing properties.展开更多
Dy3+ doped Mn-Zn ferrites Mn0.3Zn0.7Fe2-xDyxO4(x=0,0.01,0.02,0.03,0.04)were prepared by the conventional solid-state reaction.The crystal structure,surface morphology and electromagnetic properties of the calcined sam...Dy3+ doped Mn-Zn ferrites Mn0.3Zn0.7Fe2-xDyxO4(x=0,0.01,0.02,0.03,0.04)were prepared by the conventional solid-state reaction.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM) and network analyzer(Agilent 8722ET).All the XRD patterns showed the single phase of the spinel-type ferrite without other intermediate when x≤0.03.The average crystallite size was about 44?56 nm.The mi...展开更多
The electromagnetic and microwave absorbing properties of FeCoB powder composites prepared by sin- gle-roller melt-spinning and mechanical milling processes were investigated in this paper. The result indicates that t...The electromagnetic and microwave absorbing properties of FeCoB powder composites prepared by sin- gle-roller melt-spinning and mechanical milling processes were investigated in this paper. The result indicates that the flake-like powders are obtained. As milling time increases, the flake-like powder particles tend to agglomerate, causing the flake-like powders decrease gradually. The milling time plays an important role in the electromagnetic parameters which relates to the shape and size of the powder particles. The calculation shows that the sample milled for 6 h could achieve an optimal reflection loss of -11.5 dB at 5.8 GHz, with mass fraction of 83 % and a matching thickness of 1.8 mm. The result also indicates that the microwave absorbing properties of the FeCoB powder composites are adjustable by changing their thickness, and can be applied as a thinner microwave absorbing material in the range of 2-8 GHz.展开更多
Ba 1 x Dy x Co 2 Fe 16 O 27 （x = 0.00, 0.05, 0.10, 0.15, and 0.20） was prepared by the solid-state method. The phase structure was studied using powder X-ray diffraction （XRD）, the electromagnetic properties were ...Ba 1 x Dy x Co 2 Fe 16 O 27 （x = 0.00, 0.05, 0.10, 0.15, and 0.20） was prepared by the solid-state method. The phase structure was studied using powder X-ray diffraction （XRD）, the electromagnetic properties were measured, and the reflection loss of Dy 3＋ -doped ferrite material was calculated using electromagnetic parameters by the transmission line theory. All XRD patterns showed the single phase of the magnetoplumbite barium ferrite without other intermediate phase when x ≤ 0.15. The values of ε ′ and ε ″ increased slightly with Dy 3＋ ions doping. The values of μ″ and μ′ were improved with Dy 3＋ doping, exhibiting excellent microwave magnetic performance. The reasons have also been discussed using the electromagnetic theory. Dy substitution could increase microwave-absorbing performance and broaden frequency band （reflection loss （RL） -10 dB）, and the absorbing peak shifted to high-frequency position. When x = 0.2, ferrite layer exhibited the most excellent microwave-absorbing performance at a thin matching thickness of 1.5 mm. The peak value of RL was around -15 dB, and the frequency band （RL -10 dB） was about 7 GHz （from 8 to 15 GHz）.展开更多
The spinel cobalt chromium zinc ferrites（Co0.7Cr0.1Zn0.2Fe2O4） and the polyaniline（PANI）-Co0.7Cr0.1Zn0.2Fe2O4 composites were prepared by polyacrylamide gel and an in situ polymerization method,respectively.The st...The spinel cobalt chromium zinc ferrites（Co0.7Cr0.1Zn0.2Fe2O4） and the polyaniline（PANI）-Co0.7Cr0.1Zn0.2Fe2O4 composites were prepared by polyacrylamide gel and an in situ polymerization method,respectively.The structure of the synthesized material was characterized by X-ray diffraction（XRD） and Fourier transform infrared spectrometer（FTIR）,which shows that the spinel Co0.7Cr0.1Zn0.2Fe2O4 ferrites and the PANI Co0.7Cr0.1Zn0.2Fe2O4 composites are obtained.As a small amount of Co^2＋ in the octahedron ferrite is replaced by Cr^3＋,the lattice constant of Co0.8Cr0.2Zn0.2Fe2O4 ferrites reduces from0.8409 to 0.8377 nm.The magnetic properties of the two materials were investigated by vibrating sample magnetometer（VSM）.The VSM results confirm that the saturation magnetization（Ms）,remanent magnetization（Mr） and coercive force（Hc） of the PANI-Co0.7Cr0.1Zn0.2Fe2O4composites are 8.80 mA·m^2·g^-1,3.14 mA·m^2·g^-1 and37.22 kA·m^-1,respectively,which are smaller than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.The microwave absorbing capability of the two materials was studied by waveguide method.In the frequency range of 5-20 GHz,two reflection loss maximum values of the PANI-Co0.7Cr0.1Zn0.2Fe2O4 composites appear at 14.1 and 17.9 GHz with-13.17 and-15.36 dB,respectively,which are obviously higher than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.展开更多
Foam structure materials are well known for their lightweight,efficient,and broadband microwave absorption properties compared to bulk material.However,little has been understood about the effect of a foam structure o...Foam structure materials are well known for their lightweight,efficient,and broadband microwave absorption properties compared to bulk material.However,little has been understood about the effect of a foam structure on the absorption performance of the foam material.In this study,the role of foam structure properties of the silicon carbide/carbon(SiC/C)foam material on microwave absorption is explored using experiment and simulation.We find that the foam structure of SiC/C foam material causes diffraction,multiple reflections,improves the interfacial polarization,and compatibilization.The absorption performance of SiC/C foam material is also studied.The-10 dB effective absorption bandwidth can be adjusted from 4.0 GHz to 18 GHz by tuning SiC/C foam material thickness to 3-7 mm.Therefore,the foam structure design is an effective way to improve the absorption performance of the SiC/C foam material.展开更多
The ErxHo（2-x）Fe（17）（x = 0.0, 0.1,0.2, 0.3, 0.4） powders were prepared by arc melting and high energy ball milling method. The influence of the Er substitution on phase structure, morphology, saturation magnetiz...The ErxHo（2-x）Fe（17）（x = 0.0, 0.1,0.2, 0.3, 0.4） powders were prepared by arc melting and high energy ball milling method. The influence of the Er substitution on phase structure, morphology, saturation magnetization,electromagnetic parameters was investigated by X-ray diffraction（XRD）,scanning electron microscopy（SEM）, vibrating sample magnetometer（VSM） and vector network analyzer（VNA）,respectively. The results show that the saturation magnetization increases and the average particle size increases with the increase of Er content. The minimum absorption peak frequency shifts towards a lower frequency region with the increase of Er content. The ErxHo2-xFe17 powder can achieve the minimum RL of-24.07 dB at 6.96 GHz with a thickness of 2.0 mm and the minimum RL is less than-20 dB at the thickness range from 2.0 to 3.0 mm. The minimum RL of ErxHo2-xFe17 is-37.26 dB at5.68 GHz and the frequency bandwidth of R〈-10 dB reaches about 1.2 GHz with a thickness of 2.4 mm.And the microwave absorbing properties of the composite with different weight ratios of Er0.3Ho1.7Fe17/graphene were researched. The microwave absorbing peaks of the composite shift to lower frequency with the increase of graphene content. The values of the minimum RL of ErxHo2-xFe17/graphene are close to-10 dB with absorbing coating thicknesses increased.展开更多
Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromag...Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromagnetic parameters of these flower-like Ni were measured with vector network analyzer at 2-18 GHz frequency and the reflection losses （RL） with different sample thicknesses were calculated. The results indicate that the flower-like nickel-wax composites with the sample thickness less than 2 mm show excellent absorbing ability. This result is expected to play a guiding role in the preparation of the highly efficient absorber.展开更多
Microwave absorption properties of spherical NiO particles and Co0.2Ni0.4Zn0.4Fe2O4（CNZF） ferrites with single-layer and double-layer absorbers were studied in the frequency range of 2–18 GHz. The spherical NiO par...Microwave absorption properties of spherical NiO particles and Co0.2Ni0.4Zn0.4Fe2O4（CNZF） ferrites with single-layer and double-layer absorbers were studied in the frequency range of 2–18 GHz. The spherical NiO particles were synthesized by using a hydrothermal process, while the CNZF powders were prepared by using a sol–gel autoignition method. The double-layer absorbers, composed of 30 wt% NiO as matching layer and 30 wt% CNZF as absorption layer,with a total thickness of 3.2 mm, exhibited a maximum reflection loss（RL） of –67.0 d B at 9.2 GHz and an effective absorbing bandwidth below –10 d B to be 3.9 GHz from 7.0 to 10.9 GHz. The excellent microwave absorption performance of the double-layer absorbers should be ascribed to the high impedance matching ratio, the great microwave attenuation capability, and well-coupled layer.展开更多
The influences of BaCu(B2O5)(BCB)addition on sintering,microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry,scanning electron microscopy and microwave ...The influences of BaCu(B2O5)(BCB)addition on sintering,microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry,scanning electron microscopy and microwave dielectric measurements.The experimental results show that a small amount of BaCu(B2O5)addition can effectively reduce the sintering temperature to 900℃,and induce only a limited degradation of the microwave dielectric properties.Typically,the best microwave dielectric properties of er24.5,Q×f=24622 GHz,rf=4.2×10-6℃-1 are obtained for 1.0%BCB-doped Li2MgTi3O8 ceramics sintered at 900℃for 3 h.The BCB-doped Li2MgTi3O8 ceramics can be compatible with Ag electrode,which may be a strong candidate for low temperature co-fired ceramics applications.展开更多
The manganite perovskite polycrystal samples of （La1-xDyx）2/3Sr1/3MnO3 （x = 0, 0.1, 0.2, 0.35, and 0.5） doped with Dy were prepared by solid state reaction in atmosphere to measure their X-ray diffraction （XRD） ...The manganite perovskite polycrystal samples of （La1-xDyx）2/3Sr1/3MnO3 （x = 0, 0.1, 0.2, 0.35, and 0.5） doped with Dy were prepared by solid state reaction in atmosphere to measure their X-ray diffraction （XRD） patterns, scanning electric microscope （SEM） images, infrared absorption spectra, and microwave electromagnetic properties. The displacement of the XRD peaks of the samples was found, and the 2θ increases from 0.05o to 0.5o. The grains of undoped La2/3Sr1/3MnO3 not only have the greatest size, but also the most regular shape. The size of the grains decreases as the Dy doping content increases from 0 to 0.5. The infrared absorption spectra of all samples were measured at room temperature. An absorption peak corresponding to the stretching vibration mode of Mn-O bonds appears within the range of 591-629 cm-1. The absorption peak shifts from a higher frequency to a lower one with the decrease of the average ionic radius of A-site. The frequency de- pendence of microwave-absorbing properties, imaginary components of the complex magnetic permeability μ＂ and dielectric permeability ε＂ for all samples was measured at room temperature from 8 to 13 GHz. The results show that the loss of microwave absorption can be attrib- uted to both the magnetic and electric losses. The increase of Dy content not only enhances the microwave absorption but also causes the displacement of the absorption peaks.展开更多
Magnesium-substituted MnZn ferrites with composition of Mn0.4Zn0.6MgxFe（2-x）O4（x=0.00,0.05） were prepared by citrate-EDTA（ethylenediamine tetraacetic acid） complexing method.The crystal structure,surface morphol...Magnesium-substituted MnZn ferrites with composition of Mn0.4Zn0.6MgxFe（2-x）O4（x=0.00,0.05） were prepared by citrate-EDTA（ethylenediamine tetraacetic acid） complexing method.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction（XRD） analysis,scanning electron microscopy（SEM） and network analyzer（Agilent 8722ET）.All the XRD patterns showed the single phase of the spinel-type MnZn ferrite without other intermediate phase.The lattice parameter and average particle size increased with the substitution of magnesium.The microwave electromagnetic properties of the samples have been studied at the frequency range from 2 to 18 GHz.It was shown that the values of ε′ and ε″ decreased slightly with the substitution of magnesium.The values of μ′ and μ″ were improved significantly,and the peak of μ″ shifted to low frequency with Mg2＋ ions substituting.Furthermore,the reasons have also been discussed by using electromagnetic theory.The reflection loss（RL） ascended after magnesium was substituted.Magnesium-substituted ferrite had excellent microwave absorption properties.The frequency（with respect to-10 dB） started from 11.3 GHz,and the bandwidth reached about 3.5 GHz.The peak value of RL was about-19 dB at a matching thickness of 3.1 mm.展开更多
The effects of ZnO-B2O3 （ZB2） on the sintering behavior and microwave dielectric properties of （Ca0.254Li0.19Sm0.14）TiO3 ceramics were investigated. The densities of the specimens reached the maximum value by addi...The effects of ZnO-B2O3 （ZB2） on the sintering behavior and microwave dielectric properties of （Ca0.254Li0.19Sm0.14）TiO3 ceramics were investigated. The densities of the specimens reached the maximum value by adding 3 wt.% ZB2 and then decreased. The sintering temperature of the specimens was lowered from 1300 to 1100℃ without degradation of the microwave dielectric properties. The （Ca0.254Li0.19Sm0.14）TiO3＋ 3 wt.% ZB2 sintered at 1100℃ for 3 h showed good microwave dielectric properties, εr= 108.2, Qf= 6545 GHz, and rf= 6.5 ppm/℃, respectively, indicating that ZB2 was an effective sintering aid to improve the densification and microwave dielectric properties of （Ca0.254Li0.19Sm0.14）TiO3 ceramics.展开更多
The composites of Ce-Co-based alloys doped with La content were fabricated via a vacuum arc melting method.The influences of La addition on microstructure,electromagnetic parameters,magnetic property and microwave abs...The composites of Ce-Co-based alloys doped with La content were fabricated via a vacuum arc melting method.The influences of La addition on microstructure,electromagnetic parameters,magnetic property and microwave absorbing property were measured by the corresponding equipment.The morphology characteristics manifest that all samples display sheet structure,and the average particle size of alloy powders increases with increasing La content The saturation magnetization(MS) decreases with increasing La addition as a whole.The minimum reflection loss(RL) of La0.4Ce1.6Co17 alloy powder about-42.29 dB can be obtained about-42.29 dB at 7.84 GHz with the matching thickness of 1.8 mm,and the corresponding effective bandwidth can achieve about 2.24 GHz.In addition,the minimum RL frequency moves towards a lower frequency region as the La content increases.The minimum RL of La0.3Ce1.7Co17alloy powder is less than-20 dB ranging from 1.2 to 2.4 mm in the whole 4-16 GHz.The maximum bandwidth can reach about 4.88 GHz at the given thickness of 1.2 mm.In general,these all indicate that the La addition is beneficial to improving the microwave absorbing performance in both effective bandwidth and absorption intensity.展开更多
文摘Ba2ZnxCo2-xFe12O22 hexaferrites with x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0 were prepared by citrate sol-gel process. The complex dielectric constant and complex permeability of hexaferrites were studied as functions of the measuring frequency, composition and sintering temperature in the range 100 MHz similar to 6 GHz. The natural resonance phenomenon is observed in mu' spectrum for all Y-type hexaferrites, which resonance frequency is dependent on zinc content and firing temperature. The natural resonance frequencies Of Co2Y hexaferrite were calculated, which is in agreement with the measuring results. The reflection loss of those ferrites is measuring frequency as well as absorber thickness dependent, and the higher the frequency and the thickness are, the higher the reflection loss is.
文摘The paper presents a comparative study on the electric, dielectric and microwave properties of natural rubber based composites comprising dual phase fillers prepared from furnace carbon black or conductive carbon black with a different amount of silica. It has been established that, the specifics of the carbon phase have a marked strong effect upon the properties mentioned above. The interpenetration of the two filler phases and the grade of isolation of the conductive carbon phase by the dielectric one depend on the ratio between them. On the other hand, that leads to a change in all properties of the studied composites, which allows tailoring those characteristics.
基金supported by the National Natural Science Foundation of China(Grant Nos 50371029 and 50771047)the Program for the New Century Excellent Talents in University of the Ministry of Education,China(Grant No NCET20420702)the Natural Science Foundation for the Distinguished Scholars of Hubei Province,China(Grant No 2005ABB002)
文摘A single layer of CoFeB and a multilayer of CoFeB MgO films are prepared by means of DC/RF magnetron sputter deposition. The excellent microwave properties and high electrical resistivity are simultaneously achieved in the discontinuous multilayer structure of [Co44Fe44B12（0.7nm）/MgO（0.4nm）]40 film. This film has a high permeability （μ′） （larger than 100 below 2.1 GHz）, a high magnetic loss （μ″） （larger than 100 in a range from 1.5 to 3.3GHz）, a resistivity of 3.3 × 10^3μΩ. cm, a saturation magnetization of 1.2 T, and an in-plane uniaxial anisotropy field of 5.5 kA/m. The microstructure and the surface topography of the film are also analysed. The relatively large surface roughness for the discontinuous film is responsible for the wide frequency band of magnetic loss. The magnetic loss and the high resistivity indicate that the discontinuous CoFeB MgO multilayer film has potential applications in microwave absorbers and electromagnetic interference （EMI） shielding materials in a GHz frequency range.
基金supported by the National Natural Science Foundation of China (No.59995320.4).
文摘BaZnzCo2-zFe16O27/SiO2 microcrystalline glass ceramics with Z=0.0, 0.5, 0.8 and 1.1 were prepared at temperature 1200℃ for 5h by citrate sol-gel process. The complex dielectric constant and complex permeability of BaZnzCo2-zFe16 O27/SiO2-paraffin wax composites had been measured. Both the complex dielectric constant and dielectric loss exhibit almost no variation with frequency in 0.1-6.0GHz. The real part of permeability decreases with increasing frequency for all samples, and the imaginary part of permeability exhibits a clear resonance peak at 1.44GHz for Co2 W/SiO2, 1.32GHz for Zn0.5Co1.5 W/SiO2, 1.20GHz for Zn0.8Co1.2W/SiO2, and 1.08GHz for Zn1.1 Co0.9 W/SiO2. It is also showed that the content of zinc has a close effect on the magnetic properties of BaZnzCo2-zFe16O27/SiO2 microcrystalline glass ceramics, the greater the zinc content, the higher the values of imaginary part of permeability and magnetic loss.
基金The National Natural Science Foundation of China(No.51205282)
文摘In order to improve the absorbing properties of M- type barium ferrite absorbing materials, M-type barium ferrite/graphene oxide composites with different graphene oxide contents were synthesized by the sol-gel autocombustion method. X-ray diffraction （XRD）, a scanning electronic microscopy （ SEM ）, a physical properties measurement system （PPMS-9）, and a vector network analyzer were used to analyze their structure, surface morphology, magnetic and absorbing properties, respectively. The results show that the absorbing band of the composite absorbing material is widened and the absorbing strength is increased compared with the pure M-type barium ferrite. The sample with the content of doped graphene oxide of 3% has the minimum reflectivity at 10 to 18 GHz frequencies. Hence, the doped graphene oxide effectively improves the absorbing properties of M-type barium ferrite.
基金Project(51371067)supported by the National Natural Science Foundation of China
文摘Coaxially dielectric samples consisting of different packing ratios of glass-covered Fe73.5Si13.5B9Nb3Cu1 amorphous wires embedded in a paraffin wax matrix were fabricated, and the influence of short-wire packing ratio (3%-9% in mass fraction) and thickness (1-7 mm) on the microwave absorption properties was systematically investigated in microwave frequency range of 2-18 GHz. X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and scalar network analyzer (SNA) were used for characterizing microstructure and evaluating microwave absorption properties. Experimental results show the significant frequency (6-18 GHz) dependence of the complex relative permeability and permittivity. The reflection loss (RL) with different thickness and short-wire packing ratio reveals that the composite sample containing 7% exhibits better microwave absorption behavior with its minimum value of RL reaching-34 dB in thickness of 3 mm at 14 GHz. Therefore, it is significantly useful to develop microwire-dielectric materials with much wider absorption band for microwave absorption applications.
基金financially supported by the National Natural Science Foundation of China(No.51103125)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(Chemistry)+2 种基金the Natural Science Foundation of Yangzhou(No.YZ2014043)the Science Innovative Foundation of Yangzhou University(No.2014CXJ017)the Graduate Student Innovation foundation of Yangzhou University(No.CXLX 1413)
文摘La-doped Sr-hexaferrite（Sr（1-x）LaxFe（12）O（19））（x=0.05,0.10,0.15,0.20） nanopowders with particle size ranging from 80 to 110 nm were successfully synthesized by sol-gel auto-combustion. The phase formation temperature increases, while the particle size decreases as the Ladoping content goes up. The partial substitution of Sr^（2＋） by La^（3＋） results in the suppression effects on the growth-up of the crystallites and the enhancement of the electron hopping between Fe^（3＋） with different valences, which leads to the improvement in the dielectric loss and magnetic loss.Therefore, both the microwave absorbing abilities and absorbing frequency ranges are tuned by La-doping. The synthesized Sr-hexaferrite nanopowders with doping element content of 0.10 demonstrate the fine broad microwave absorbing properties.
基金supported by the National Defence Fundamental Research (MKPT-232)
文摘Dy3+ doped Mn-Zn ferrites Mn0.3Zn0.7Fe2-xDyxO4(x=0,0.01,0.02,0.03,0.04)were prepared by the conventional solid-state reaction.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM) and network analyzer(Agilent 8722ET).All the XRD patterns showed the single phase of the spinel-type ferrite without other intermediate when x≤0.03.The average crystallite size was about 44?56 nm.The mi...
基金financially supported by the National Hi-tech R&D Project Supporting Programs Funded by Ministry of Science&Technology of China(No.2012AA063202)the National Natural Science Foundation of China(Nos.50972013,50802008,and 51004011)+1 种基金the National Key Project of Scientific and Technical Supporting Programs Funded by Ministry of Science&Technology of China(Nos.2012BAC02B01,2012BAC12B05,2011BAE13B07,and 2011BAC10B02)the Guangdong Province&Ministry of Education Industry-Study-Research United Project(No.2009A090100017)
文摘The electromagnetic and microwave absorbing properties of FeCoB powder composites prepared by sin- gle-roller melt-spinning and mechanical milling processes were investigated in this paper. The result indicates that the flake-like powders are obtained. As milling time increases, the flake-like powder particles tend to agglomerate, causing the flake-like powders decrease gradually. The milling time plays an important role in the electromagnetic parameters which relates to the shape and size of the powder particles. The calculation shows that the sample milled for 6 h could achieve an optimal reflection loss of -11.5 dB at 5.8 GHz, with mass fraction of 83 % and a matching thickness of 1.8 mm. The result also indicates that the microwave absorbing properties of the FeCoB powder composites are adjustable by changing their thickness, and can be applied as a thinner microwave absorbing material in the range of 2-8 GHz.
基金the University Natural Science Fund of Jiangsu Province, China (No. 10KJB430008)the Advanced Project of the General Reserve Department of PLA for the financial support
文摘Ba 1 x Dy x Co 2 Fe 16 O 27 （x = 0.00, 0.05, 0.10, 0.15, and 0.20） was prepared by the solid-state method. The phase structure was studied using powder X-ray diffraction （XRD）, the electromagnetic properties were measured, and the reflection loss of Dy 3＋ -doped ferrite material was calculated using electromagnetic parameters by the transmission line theory. All XRD patterns showed the single phase of the magnetoplumbite barium ferrite without other intermediate phase when x ≤ 0.15. The values of ε ′ and ε ″ increased slightly with Dy 3＋ ions doping. The values of μ″ and μ′ were improved with Dy 3＋ doping, exhibiting excellent microwave magnetic performance. The reasons have also been discussed using the electromagnetic theory. Dy substitution could increase microwave-absorbing performance and broaden frequency band （reflection loss （RL） -10 dB）, and the absorbing peak shifted to high-frequency position. When x = 0.2, ferrite layer exhibited the most excellent microwave-absorbing performance at a thin matching thickness of 1.5 mm. The peak value of RL was around -15 dB, and the frequency band （RL -10 dB） was about 7 GHz （from 8 to 15 GHz）.
基金financially supported by the Natural Science Foundation of Liaoning Province(No.2014020094)the Key Laboratory Construction Fund of Shenyang(No.F14187-1-00)
文摘The spinel cobalt chromium zinc ferrites（Co0.7Cr0.1Zn0.2Fe2O4） and the polyaniline（PANI）-Co0.7Cr0.1Zn0.2Fe2O4 composites were prepared by polyacrylamide gel and an in situ polymerization method,respectively.The structure of the synthesized material was characterized by X-ray diffraction（XRD） and Fourier transform infrared spectrometer（FTIR）,which shows that the spinel Co0.7Cr0.1Zn0.2Fe2O4 ferrites and the PANI Co0.7Cr0.1Zn0.2Fe2O4 composites are obtained.As a small amount of Co^2＋ in the octahedron ferrite is replaced by Cr^3＋,the lattice constant of Co0.8Cr0.2Zn0.2Fe2O4 ferrites reduces from0.8409 to 0.8377 nm.The magnetic properties of the two materials were investigated by vibrating sample magnetometer（VSM）.The VSM results confirm that the saturation magnetization（Ms）,remanent magnetization（Mr） and coercive force（Hc） of the PANI-Co0.7Cr0.1Zn0.2Fe2O4composites are 8.80 mA·m^2·g^-1,3.14 mA·m^2·g^-1 and37.22 kA·m^-1,respectively,which are smaller than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.The microwave absorbing capability of the two materials was studied by waveguide method.In the frequency range of 5-20 GHz,two reflection loss maximum values of the PANI-Co0.7Cr0.1Zn0.2Fe2O4 composites appear at 14.1 and 17.9 GHz with-13.17 and-15.36 dB,respectively,which are obviously higher than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.
文摘Foam structure materials are well known for their lightweight,efficient,and broadband microwave absorption properties compared to bulk material.However,little has been understood about the effect of a foam structure on the absorption performance of the foam material.In this study,the role of foam structure properties of the silicon carbide/carbon(SiC/C)foam material on microwave absorption is explored using experiment and simulation.We find that the foam structure of SiC/C foam material causes diffraction,multiple reflections,improves the interfacial polarization,and compatibilization.The absorption performance of SiC/C foam material is also studied.The-10 dB effective absorption bandwidth can be adjusted from 4.0 GHz to 18 GHz by tuning SiC/C foam material thickness to 3-7 mm.Therefore,the foam structure design is an effective way to improve the absorption performance of the SiC/C foam material.
基金supported by the National Natural Science Foundation of China(51361007)Guangxi Natural Science Foundation(2014GXNSFAA118317)+2 种基金Scientific Research Project of Guangxi Education Department(YB2014139)Innovation Project of GUET Graduate Education(YJCXS 201566)Guangxi Key Laboratory of Information Materials(131010-Z)
文摘The ErxHo（2-x）Fe（17）（x = 0.0, 0.1,0.2, 0.3, 0.4） powders were prepared by arc melting and high energy ball milling method. The influence of the Er substitution on phase structure, morphology, saturation magnetization,electromagnetic parameters was investigated by X-ray diffraction（XRD）,scanning electron microscopy（SEM）, vibrating sample magnetometer（VSM） and vector network analyzer（VNA）,respectively. The results show that the saturation magnetization increases and the average particle size increases with the increase of Er content. The minimum absorption peak frequency shifts towards a lower frequency region with the increase of Er content. The ErxHo2-xFe17 powder can achieve the minimum RL of-24.07 dB at 6.96 GHz with a thickness of 2.0 mm and the minimum RL is less than-20 dB at the thickness range from 2.0 to 3.0 mm. The minimum RL of ErxHo2-xFe17 is-37.26 dB at5.68 GHz and the frequency bandwidth of R〈-10 dB reaches about 1.2 GHz with a thickness of 2.4 mm.And the microwave absorbing properties of the composite with different weight ratios of Er0.3Ho1.7Fe17/graphene were researched. The microwave absorbing peaks of the composite shift to lower frequency with the increase of graphene content. The values of the minimum RL of ErxHo2-xFe17/graphene are close to-10 dB with absorbing coating thicknesses increased.
基金Project(JC201006020838A)supported by the Basic Research Funds of Science and Technology Foundation of Shenzhen,China
文摘Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromagnetic parameters of these flower-like Ni were measured with vector network analyzer at 2-18 GHz frequency and the reflection losses （RL） with different sample thicknesses were calculated. The results indicate that the flower-like nickel-wax composites with the sample thickness less than 2 mm show excellent absorbing ability. This result is expected to play a guiding role in the preparation of the highly efficient absorber.
基金financially supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology (ASMA201405)+1 种基金the National Natural Science Foundation of China (51672129)Singapore MOE AcRF Tier 1 Project (Research ID 477)
文摘Microwave absorption properties of spherical NiO particles and Co0.2Ni0.4Zn0.4Fe2O4（CNZF） ferrites with single-layer and double-layer absorbers were studied in the frequency range of 2–18 GHz. The spherical NiO particles were synthesized by using a hydrothermal process, while the CNZF powders were prepared by using a sol–gel autoignition method. The double-layer absorbers, composed of 30 wt% NiO as matching layer and 30 wt% CNZF as absorption layer,with a total thickness of 3.2 mm, exhibited a maximum reflection loss（RL） of –67.0 d B at 9.2 GHz and an effective absorbing bandwidth below –10 d B to be 3.9 GHz from 7.0 to 10.9 GHz. The excellent microwave absorption performance of the double-layer absorbers should be ascribed to the high impedance matching ratio, the great microwave attenuation capability, and well-coupled layer.
基金Project(2010GXNSFA013029)supported by the Natural Science Foundation of Guangxi Province,ChinaProject(101059529)supported by National Undergraduate Innovation Program of the Ministry of Education of China
文摘The influences of BaCu(B2O5)(BCB)addition on sintering,microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry,scanning electron microscopy and microwave dielectric measurements.The experimental results show that a small amount of BaCu(B2O5)addition can effectively reduce the sintering temperature to 900℃,and induce only a limited degradation of the microwave dielectric properties.Typically,the best microwave dielectric properties of er24.5,Q×f=24622 GHz,rf=4.2×10-6℃-1 are obtained for 1.0%BCB-doped Li2MgTi3O8 ceramics sintered at 900℃for 3 h.The BCB-doped Li2MgTi3O8 ceramics can be compatible with Ag electrode,which may be a strong candidate for low temperature co-fired ceramics applications.
基金supported by the National Natural Science Foundation of China (No. 60561001)the Natural Science Foundation of Inner Mongolia Autonomous Region, China (No. 200408020105)+1 种基金the Program for New Century Excellent Talents in Universities (No. NCET-05-0272)College Science and Technology Re-search Project of Inner Mongolia Autonomous Region, China (No. NJ04094)
文摘The manganite perovskite polycrystal samples of （La1-xDyx）2/3Sr1/3MnO3 （x = 0, 0.1, 0.2, 0.35, and 0.5） doped with Dy were prepared by solid state reaction in atmosphere to measure their X-ray diffraction （XRD） patterns, scanning electric microscope （SEM） images, infrared absorption spectra, and microwave electromagnetic properties. The displacement of the XRD peaks of the samples was found, and the 2θ increases from 0.05o to 0.5o. The grains of undoped La2/3Sr1/3MnO3 not only have the greatest size, but also the most regular shape. The size of the grains decreases as the Dy doping content increases from 0 to 0.5. The infrared absorption spectra of all samples were measured at room temperature. An absorption peak corresponding to the stretching vibration mode of Mn-O bonds appears within the range of 591-629 cm-1. The absorption peak shifts from a higher frequency to a lower one with the decrease of the average ionic radius of A-site. The frequency de- pendence of microwave-absorbing properties, imaginary components of the complex magnetic permeability μ＂ and dielectric permeability ε＂ for all samples was measured at room temperature from 8 to 13 GHz. The results show that the loss of microwave absorption can be attrib- uted to both the magnetic and electric losses. The increase of Dy content not only enhances the microwave absorption but also causes the displacement of the absorption peaks.
基金supported by the National Defence Fundamental Research of China under grant No.MKPT-232
文摘Magnesium-substituted MnZn ferrites with composition of Mn0.4Zn0.6MgxFe（2-x）O4（x=0.00,0.05） were prepared by citrate-EDTA（ethylenediamine tetraacetic acid） complexing method.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction（XRD） analysis,scanning electron microscopy（SEM） and network analyzer（Agilent 8722ET）.All the XRD patterns showed the single phase of the spinel-type MnZn ferrite without other intermediate phase.The lattice parameter and average particle size increased with the substitution of magnesium.The microwave electromagnetic properties of the samples have been studied at the frequency range from 2 to 18 GHz.It was shown that the values of ε′ and ε″ decreased slightly with the substitution of magnesium.The values of μ′ and μ″ were improved significantly,and the peak of μ″ shifted to low frequency with Mg2＋ ions substituting.Furthermore,the reasons have also been discussed by using electromagnetic theory.The reflection loss（RL） ascended after magnesium was substituted.Magnesium-substituted ferrite had excellent microwave absorption properties.The frequency（with respect to-10 dB） started from 11.3 GHz,and the bandwidth reached about 3.5 GHz.The peak value of RL was about-19 dB at a matching thickness of 3.1 mm.
基金supported by the National Natural Science Foundation of China (No. 50572008)
文摘The effects of ZnO-B2O3 （ZB2） on the sintering behavior and microwave dielectric properties of （Ca0.254Li0.19Sm0.14）TiO3 ceramics were investigated. The densities of the specimens reached the maximum value by adding 3 wt.% ZB2 and then decreased. The sintering temperature of the specimens was lowered from 1300 to 1100℃ without degradation of the microwave dielectric properties. The （Ca0.254Li0.19Sm0.14）TiO3＋ 3 wt.% ZB2 sintered at 1100℃ for 3 h showed good microwave dielectric properties, εr= 108.2, Qf= 6545 GHz, and rf= 6.5 ppm/℃, respectively, indicating that ZB2 was an effective sintering aid to improve the densification and microwave dielectric properties of （Ca0.254Li0.19Sm0.14）TiO3 ceramics.
基金Project supported by the National Natural Science Foundation of China (51361007)2017 Director Fund of Guangxi Key Laboratory of Wireless Wideband Communication and Signal Processing (GXKL06170107)。
文摘The composites of Ce-Co-based alloys doped with La content were fabricated via a vacuum arc melting method.The influences of La addition on microstructure,electromagnetic parameters,magnetic property and microwave absorbing property were measured by the corresponding equipment.The morphology characteristics manifest that all samples display sheet structure,and the average particle size of alloy powders increases with increasing La content The saturation magnetization(MS) decreases with increasing La addition as a whole.The minimum reflection loss(RL) of La0.4Ce1.6Co17 alloy powder about-42.29 dB can be obtained about-42.29 dB at 7.84 GHz with the matching thickness of 1.8 mm,and the corresponding effective bandwidth can achieve about 2.24 GHz.In addition,the minimum RL frequency moves towards a lower frequency region as the La content increases.The minimum RL of La0.3Ce1.7Co17alloy powder is less than-20 dB ranging from 1.2 to 2.4 mm in the whole 4-16 GHz.The maximum bandwidth can reach about 4.88 GHz at the given thickness of 1.2 mm.In general,these all indicate that the La addition is beneficial to improving the microwave absorbing performance in both effective bandwidth and absorption intensity.
