Magnesium-substituted Mn0.8Zn0.2Fe2O4 ferrite is synthesized by the sol–gel combustion method using citrate acid as the complex agent. The electromagnetic absorbing behaviors of ferrite/polymer coatings fabricated by...Magnesium-substituted Mn0.8Zn0.2Fe2O4 ferrite is synthesized by the sol–gel combustion method using citrate acid as the complex agent. The electromagnetic absorbing behaviors of ferrite/polymer coatings fabricated by dispersing Mn–Zn ferrite into epoxy resin （EP） are studied. The microstructure and morphology are characterized by X-ray diffraction and scanning electron microscope. Complex permittivity, complex permeability, and reflection loss of ferrite/EP composite coating are investigated in a low frequency range. It is found that the prepared ferrite particles are traditional cubic spinel ferrite particles with an average size of 200 nm. The results reveal that the electromagnetic microwave absorbing properties are significantly influenced by the weight ratio of ferrite to polymer. The composites with a weight ratio of ferrite/polymer being 3：20 have a maximum reflection loss of –16 dB and wide absorbing band. Thus, the Mn–Zn ferrite is the potential candidate in electromagnetic absorbing application in the low frequency range （10 MHz–1 GHz）.展开更多
The electromagnetic parameters of microwave absorbing materials are important criteria when appraising the properties of absorbents. For reconstruction of parameters which belongs to the inverse scattering problem, th...The electromagnetic parameters of microwave absorbing materials are important criteria when appraising the properties of absorbents. For reconstruction of parameters which belongs to the inverse scattering problem, the test data in requirement of traditional impedance method are "just enough" and not "redundant" to comprehensively evaluate the electromagnetic properties of materials. A novel optimization approach involving multiple impedance measurements is introduced in this paper to implement automatic measurement for electromagnetic parameters on microwave slot-line. Some results for standard samples and microwave absorbing materials are given.展开更多
The experiment samples of La1-xSrxMn1-y FeyO3（x = 0. 15, 0.20, 0.23; y = 0. 10, 0. 12, 0.14, 0.16） were prepared by sol-gel process, and the loss tangent and absorption coefficient in the range of 2 - 18 GHz were me...The experiment samples of La1-xSrxMn1-y FeyO3（x = 0. 15, 0.20, 0.23; y = 0. 10, 0. 12, 0.14, 0.16） were prepared by sol-gel process, and the loss tangent and absorption coefficient in the range of 2 - 18 GHz were measured by HP8722 net analyzing apparatus. It is found that changing the content of Sr or Fe would effect the microwave absorbing. When the thickness of La1-x SrxMn1-y FeyO3 is 2 mm and x =0.20, y = 0.14, the capability of microwave absorbing is the best one. There are two absorption peaks; the maximum is 34 dB and effective band width with 10 dB and more reaches 6.2 GHz.展开更多
MnZn-doped W-type barium cobalt ferrite powder composites of Ba(MnZn)xCo2(1-x)Fe16O27 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) were prepared in a sol-gel process. The microwave absorbing properties of the composites in the r...MnZn-doped W-type barium cobalt ferrite powder composites of Ba(MnZn)xCo2(1-x)Fe16O27 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) were prepared in a sol-gel process. The microwave absorbing properties of the composites in the range of 2 - 18 GHz and their electromagnetic loss mechanisms were studied. The results demonstrated that the synthesized Ba(MnZn)xCo2(1-x)Fe16O27 samples possess a W-type phase of the crystal structure with a hexagonal flaky shape in micro-morphology, and the samples exhibited a soft magnetic trait that enables improving their microwave absorption properties through suitable MnZn doping. For Ba(MnZn)0.4Co1.2Fe16O27 with a thickness of 2.8 mm, the reflection loss peak was -40.7 dB at a frequency of 7.3 GHz, with a bandwidth of 6.6 GHz at a loss of less than -10 dB. The microwave absorption primarily resulted from magnetic losses caused by magnetization relaxation, domain wall resonance, and natural resonance.展开更多
La0.8Ba0.2MnO3 nano-particles were synthesized by sol-gel process, and the crystal structure and morphology were characterized by XRD and SEM, respectively. The complex permittivity and permeability were determined by...La0.8Ba0.2MnO3 nano-particles were synthesized by sol-gel process, and the crystal structure and morphology were characterized by XRD and SEM, respectively. The complex permittivity and permeability were determined by microwave vector network analyzer in the frequency range of 2-18 GHz. The relationship between reflection coefficient and microwave frequency of La0.8Ba0.2 MnO3 was calculated based on measured data. The results show that the average diameter of La0.8Ba0.2MnO3 crystal powders is about 80 nm and the crystal structure is perovskite when being calcined at 800 ℃ for 2 h. The microwave absorbing peak is 13 dB at 6.7 GHz and the effective absorbing bandwidth above 10 dB reaches 1.8 GHz for the sample with the thickness of 2.6 mm. The microwave absorption can be attributed to both the dielectric loss and the magnetic loss from the loss tangents of the sample, but the former is greater than the latter.展开更多
Microwave absorbing materials(MAMs)are playing an increasingly essential role in the development of wireless communications,high-power electronic devices,and advanced target detection technology.MAMs with a broad-band...Microwave absorbing materials(MAMs)are playing an increasingly essential role in the development of wireless communications,high-power electronic devices,and advanced target detection technology.MAMs with a broad-bandwidth response are particularly important in the area of communication security,radiation prevention,electronic reliability,and military stealth.Although considerable progress has been made in the design and preparation of MAMs with a broad-bandwidth response,a number of challenges still remain,and the structure–function relationship of MAMs is still far from being completely understood.Herein,the advances in the design and research of MAMs with a broad-bandwidth response are outlined.The main strategies for expanding the effective absorption bandwidth of MAMs are comprehensively summarized considering three perspectives:the chemical combination strategy,morphological control strategy,and macrostructure control strategy.Several important results as well as design principles and absorption mechanisms are highlighted.A coherent explanation detailing the influence of the chemical composition and structure of various materials on the microwave absorption properties of MAMs is provided.The main challenges,new opportunities,and future perspectives in this promising field are also presented.展开更多
A Y-type hexaferrite rod with the composition of Ba2COl.8Cuo.2Fe12022 was presented as an absorbing material with high absorb- anee. Its high absorbance and wide absorption band result from ferromagnetic resonance （...A Y-type hexaferrite rod with the composition of Ba2COl.8Cuo.2Fe12022 was presented as an absorbing material with high absorb- anee. Its high absorbance and wide absorption band result from ferromagnetic resonance （FMR） that is self-biased by strong shape and mag- netocrystaUine anisotropy fields. Around the FMR frequency the specimen of the ferrite rods exhibits very high absorbance and the FMR frequency can be tuned by the rod dimension. In addition to the high absorbance and the wide tunable absorption band, the microwave ab- sorber has another advantage of light weight due to the use of the ferrite rods instead of ferrite slabs.展开更多
Electromagnetic (EM) parameters (ε ′, ε ″, μ ′, μ″ ) of several M2+Fe2O4 and Fe2O3 type natural ferrites with different geological occurrences are measured in this pa-per. The measurement results show that EM ...Electromagnetic (EM) parameters (ε ′, ε ″, μ ′, μ″ ) of several M2+Fe2O4 and Fe2O3 type natural ferrites with different geological occurrences are measured in this pa-per. The measurement results show that EM parameters of a magmatic-occurring natural ferrite is very different from other types occurring from sedimentary-metamorphic iron deposit, hydrothermal vein iron deposit, outer contact of magmatic iron deposit. It has potential to be used as magnetic absorbent in microwave absorbing materials. After min-eral separation and concentration, this magmatic-occurring natural ferrite was processed into type A ferrite absorbent. Type A natural ferrite absorbent is a kind of magnetic material with low dielectric constants, high magnetic conductivity and high EM loss. Its EM pa-rameters are ε ′ = 58.60, ε ″ = 10.0, μ ′ = 1.2-1.5, μ ″ = 1.0-1.2, respectively. In order to illuminate the regulation mechanism of EM parameters, we studied the chemical and mineral composition of type A ferrite absorbent. There is high concentration of natural impurities, which regulate the EM parameters of type A ferrite greatly. For comparison, the other types of natural ferrite, single-phase magnetite and two-phase iron minerals (ilmen-ite and magnetite), have few impurity. Thus regulation mechanism of EM parameters was absent in these ferrites. As a result, the regulation of EM parameters is advantageous to develop type A natural ferrite as excellent absorbent, lowers the reflectivity coefficients and enhances the absorbing efficiency of MAM made from it. Furthermore, the impurities in type A natural ferrite and its effects on EM parameters are very difficult to simulate in the synthesize ferrite. The carbonyl-iron powder is another kind of absorbent that is used ex-tensively in MAM. To compare the absorbing properties of these two absorbent, type A natural ferrite and carbonyl-iron powder were mixed with rubber and processed into mi-crowave absorbing sheets with the same procedures and technics. The measurement results show that the microwave absorbing bandwidth of type A ferrite absorbent sheet material is larger than that of carbonyl-iron powder. The reflectivity coefficient is also im-proved in the frequency of 8-12 GHz. For the reason of low price and abundant resource, the stable performance in EM properties, type A natural ferrite absorbent is a good sub-stitute of carbonyl-iron powder in MAM.展开更多
In this paper, we focus on PHYTOPOROUS, a porous carbon material made entirely from plant-based ingredients, as a new broadband-wave absorber material that acts in the millimeter wave band. We created prototypes of th...In this paper, we focus on PHYTOPOROUS, a porous carbon material made entirely from plant-based ingredients, as a new broadband-wave absorber material that acts in the millimeter wave band. We created prototypes of thin rubber-sheet wave absorbers that contain porous carbon (PHYTOPOROUS) made from rice chaff and soybean hulls, which are both agricultural residue products that are generated in large quantities. We investigated the permittivity and reflectance characteristics of this material using the free-space time-domain method. The thin rubber-sheet wave absorber that contained PHYTOPOROUS made from soybean hulls exhibited a frequency band that was approximately 18 GHz wide and centered at 90 GHz. The return loss for this material was greater than −20 dB. This demonstrates that the material provides nearly constant reflection absorption over a wide frequency band.展开更多
A novel bunched cerium oxide(CeO_(2))was prepared and its binary composite material with multi-walled carbon nanotubes presented an excellent microwave absorbing properties.The morphology,structure,and absorbing prope...A novel bunched cerium oxide(CeO_(2))was prepared and its binary composite material with multi-walled carbon nanotubes presented an excellent microwave absorbing properties.The morphology,structure,and absorbing properties of the composite material were investigated.It was found that the minimum reflection loss(RL)of the composite material at 15.79 GHz was−45.7 dB when the thickness was 5.5 mm.It was worth noting that when the composite material was in the thickness range of 5.0-7.5 mm and the frequency was 11.36-17.77 GHz,the electromagnetic wave RL was<−30 dB,which illustrated that the composite material had a good absorbing effect over a wide thickness range.The results of the study contributed to the design and preparation of efficient microwave absorbing materials(MAM)with rare earth oxide composites and their applications,which demonstrated the importance of new composites with special structures in the field of MAM.展开更多
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20121101110014)
文摘Magnesium-substituted Mn0.8Zn0.2Fe2O4 ferrite is synthesized by the sol–gel combustion method using citrate acid as the complex agent. The electromagnetic absorbing behaviors of ferrite/polymer coatings fabricated by dispersing Mn–Zn ferrite into epoxy resin （EP） are studied. The microstructure and morphology are characterized by X-ray diffraction and scanning electron microscope. Complex permittivity, complex permeability, and reflection loss of ferrite/EP composite coating are investigated in a low frequency range. It is found that the prepared ferrite particles are traditional cubic spinel ferrite particles with an average size of 200 nm. The results reveal that the electromagnetic microwave absorbing properties are significantly influenced by the weight ratio of ferrite to polymer. The composites with a weight ratio of ferrite/polymer being 3：20 have a maximum reflection loss of –16 dB and wide absorbing band. Thus, the Mn–Zn ferrite is the potential candidate in electromagnetic absorbing application in the low frequency range （10 MHz–1 GHz）.
文摘The electromagnetic parameters of microwave absorbing materials are important criteria when appraising the properties of absorbents. For reconstruction of parameters which belongs to the inverse scattering problem, the test data in requirement of traditional impedance method are "just enough" and not "redundant" to comprehensively evaluate the electromagnetic properties of materials. A novel optimization approach involving multiple impedance measurements is introduced in this paper to implement automatic measurement for electromagnetic parameters on microwave slot-line. Some results for standard samples and microwave absorbing materials are given.
文摘The experiment samples of La1-xSrxMn1-y FeyO3（x = 0. 15, 0.20, 0.23; y = 0. 10, 0. 12, 0.14, 0.16） were prepared by sol-gel process, and the loss tangent and absorption coefficient in the range of 2 - 18 GHz were measured by HP8722 net analyzing apparatus. It is found that changing the content of Sr or Fe would effect the microwave absorbing. When the thickness of La1-x SrxMn1-y FeyO3 is 2 mm and x =0.20, y = 0.14, the capability of microwave absorbing is the best one. There are two absorption peaks; the maximum is 34 dB and effective band width with 10 dB and more reaches 6.2 GHz.
文摘MnZn-doped W-type barium cobalt ferrite powder composites of Ba(MnZn)xCo2(1-x)Fe16O27 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) were prepared in a sol-gel process. The microwave absorbing properties of the composites in the range of 2 - 18 GHz and their electromagnetic loss mechanisms were studied. The results demonstrated that the synthesized Ba(MnZn)xCo2(1-x)Fe16O27 samples possess a W-type phase of the crystal structure with a hexagonal flaky shape in micro-morphology, and the samples exhibited a soft magnetic trait that enables improving their microwave absorption properties through suitable MnZn doping. For Ba(MnZn)0.4Co1.2Fe16O27 with a thickness of 2.8 mm, the reflection loss peak was -40.7 dB at a frequency of 7.3 GHz, with a bandwidth of 6.6 GHz at a loss of less than -10 dB. The microwave absorption primarily resulted from magnetic losses caused by magnetization relaxation, domain wall resonance, and natural resonance.
基金Project(05JT1034) supported by the Planned Item of Science and Technology of Hunan Province, China
文摘La0.8Ba0.2MnO3 nano-particles were synthesized by sol-gel process, and the crystal structure and morphology were characterized by XRD and SEM, respectively. The complex permittivity and permeability were determined by microwave vector network analyzer in the frequency range of 2-18 GHz. The relationship between reflection coefficient and microwave frequency of La0.8Ba0.2 MnO3 was calculated based on measured data. The results show that the average diameter of La0.8Ba0.2MnO3 crystal powders is about 80 nm and the crystal structure is perovskite when being calcined at 800 ℃ for 2 h. The microwave absorbing peak is 13 dB at 6.7 GHz and the effective absorbing bandwidth above 10 dB reaches 1.8 GHz for the sample with the thickness of 2.6 mm. The microwave absorption can be attributed to both the dielectric loss and the magnetic loss from the loss tangents of the sample, but the former is greater than the latter.
基金supported by the National Natural Science Foundation of China(Nos.21771151 and 21931009).
文摘Microwave absorbing materials(MAMs)are playing an increasingly essential role in the development of wireless communications,high-power electronic devices,and advanced target detection technology.MAMs with a broad-bandwidth response are particularly important in the area of communication security,radiation prevention,electronic reliability,and military stealth.Although considerable progress has been made in the design and preparation of MAMs with a broad-bandwidth response,a number of challenges still remain,and the structure–function relationship of MAMs is still far from being completely understood.Herein,the advances in the design and research of MAMs with a broad-bandwidth response are outlined.The main strategies for expanding the effective absorption bandwidth of MAMs are comprehensively summarized considering three perspectives:the chemical combination strategy,morphological control strategy,and macrostructure control strategy.Several important results as well as design principles and absorption mechanisms are highlighted.A coherent explanation detailing the influence of the chemical composition and structure of various materials on the microwave absorption properties of MAMs is provided.The main challenges,new opportunities,and future perspectives in this promising field are also presented.
基金supported by the National Natural Science Foundation of China (No.50702005)the Natural Science Foundation of the Education Department of Henan Province,China (No.2010A430012)
文摘A Y-type hexaferrite rod with the composition of Ba2COl.8Cuo.2Fe12022 was presented as an absorbing material with high absorb- anee. Its high absorbance and wide absorption band result from ferromagnetic resonance （FMR） that is self-biased by strong shape and mag- netocrystaUine anisotropy fields. Around the FMR frequency the specimen of the ferrite rods exhibits very high absorbance and the FMR frequency can be tuned by the rod dimension. In addition to the high absorbance and the wide tunable absorption band, the microwave ab- sorber has another advantage of light weight due to the use of the ferrite rods instead of ferrite slabs.
文摘Electromagnetic (EM) parameters (ε ′, ε ″, μ ′, μ″ ) of several M2+Fe2O4 and Fe2O3 type natural ferrites with different geological occurrences are measured in this pa-per. The measurement results show that EM parameters of a magmatic-occurring natural ferrite is very different from other types occurring from sedimentary-metamorphic iron deposit, hydrothermal vein iron deposit, outer contact of magmatic iron deposit. It has potential to be used as magnetic absorbent in microwave absorbing materials. After min-eral separation and concentration, this magmatic-occurring natural ferrite was processed into type A ferrite absorbent. Type A natural ferrite absorbent is a kind of magnetic material with low dielectric constants, high magnetic conductivity and high EM loss. Its EM pa-rameters are ε ′ = 58.60, ε ″ = 10.0, μ ′ = 1.2-1.5, μ ″ = 1.0-1.2, respectively. In order to illuminate the regulation mechanism of EM parameters, we studied the chemical and mineral composition of type A ferrite absorbent. There is high concentration of natural impurities, which regulate the EM parameters of type A ferrite greatly. For comparison, the other types of natural ferrite, single-phase magnetite and two-phase iron minerals (ilmen-ite and magnetite), have few impurity. Thus regulation mechanism of EM parameters was absent in these ferrites. As a result, the regulation of EM parameters is advantageous to develop type A natural ferrite as excellent absorbent, lowers the reflectivity coefficients and enhances the absorbing efficiency of MAM made from it. Furthermore, the impurities in type A natural ferrite and its effects on EM parameters are very difficult to simulate in the synthesize ferrite. The carbonyl-iron powder is another kind of absorbent that is used ex-tensively in MAM. To compare the absorbing properties of these two absorbent, type A natural ferrite and carbonyl-iron powder were mixed with rubber and processed into mi-crowave absorbing sheets with the same procedures and technics. The measurement results show that the microwave absorbing bandwidth of type A ferrite absorbent sheet material is larger than that of carbonyl-iron powder. The reflectivity coefficient is also im-proved in the frequency of 8-12 GHz. For the reason of low price and abundant resource, the stable performance in EM properties, type A natural ferrite absorbent is a good sub-stitute of carbonyl-iron powder in MAM.
文摘In this paper, we focus on PHYTOPOROUS, a porous carbon material made entirely from plant-based ingredients, as a new broadband-wave absorber material that acts in the millimeter wave band. We created prototypes of thin rubber-sheet wave absorbers that contain porous carbon (PHYTOPOROUS) made from rice chaff and soybean hulls, which are both agricultural residue products that are generated in large quantities. We investigated the permittivity and reflectance characteristics of this material using the free-space time-domain method. The thin rubber-sheet wave absorber that contained PHYTOPOROUS made from soybean hulls exhibited a frequency band that was approximately 18 GHz wide and centered at 90 GHz. The return loss for this material was greater than −20 dB. This demonstrates that the material provides nearly constant reflection absorption over a wide frequency band.
文摘A novel bunched cerium oxide(CeO_(2))was prepared and its binary composite material with multi-walled carbon nanotubes presented an excellent microwave absorbing properties.The morphology,structure,and absorbing properties of the composite material were investigated.It was found that the minimum reflection loss(RL)of the composite material at 15.79 GHz was−45.7 dB when the thickness was 5.5 mm.It was worth noting that when the composite material was in the thickness range of 5.0-7.5 mm and the frequency was 11.36-17.77 GHz,the electromagnetic wave RL was<−30 dB,which illustrated that the composite material had a good absorbing effect over a wide thickness range.The results of the study contributed to the design and preparation of efficient microwave absorbing materials(MAM)with rare earth oxide composites and their applications,which demonstrated the importance of new composites with special structures in the field of MAM.
