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
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
In order to achieve an easy fabrication and considerable directional orientation, we use a sedimentation method to prepare composites consisting of Fe Si Al flakes. The flakes are dispersed in hydroxylated acrylic res...In order to achieve an easy fabrication and considerable directional orientation, we use a sedimentation method to prepare composites consisting of Fe Si Al flakes. The flakes are dispersed in hydroxylated acrylic resin solution in sonication and natural form into laminated composite samples. Then, the toroidal rings are made with the prepared laminated composite samples. Compared with random orientational Fe Si Al flakes in the composite, the complex permeability of laminated sample has been obviously improved when microwave frequency is below 4 GHz, especially for the imaginary part. A model is proposed to explain the formation reason of aligned Fe Si Al composite by this method. Damping factor（α） is calculated by the combination of the effective medium theory and Landau-Lifshitz-Gilbert equation, and the permeability of the samples is verified by these theories.展开更多
Carbonaceous nanomaterials such as carbon nanotubes （CNTs）, magnetic metal nanomaterials and semicon- ductor nanomaterials are superior candidates for microwave absorbers. Taking full advantage of the features of CN...Carbonaceous nanomaterials such as carbon nanotubes （CNTs）, magnetic metal nanomaterials and semicon- ductor nanomaterials are superior candidates for microwave absorbers. Taking full advantage of the features of CNTs, nanophase cobalt and nanophase zinc oxide, whose main microwave absorption mechanisms are based on resistance loss, magnetic loss and dielectric loss, we fabricate CNT/Co and CNT/ZnO heterostructure nanocom- posites, respectively. By using the CNTs, CNT/Co nanocomposites and CNT/ZnO nanocomposites as nanofillers, composites with polyester as matrix are prepared by in situ polymerization, and their microwave absorption per- formance is studied. It is indicated that the synergetic effects of the physic properties of different components in nano-heterostructures result in greatly enhanced microwave absorption performance in a wide frequency range. The absorption peak is increased, the absorption bandwidth is broadened, and the maximum peak shifts to a lower frequency.展开更多
The composite that can absorb the high-performance electromagnetic（EM） wave is constructed into a sandwiched structure composed of carbon black（CB）/ethylene-vinyl acetate（EVA） and Ag naowires（Ag NWs）. The Ag N...The composite that can absorb the high-performance electromagnetic（EM） wave is constructed into a sandwiched structure composed of carbon black（CB）/ethylene-vinyl acetate（EVA） and Ag naowires（Ag NWs）. The Ag NWs sandwiched between two CB/EVA layers are used to improve the absorption properties of composite. The effects of EVA-to-CB weight ratio, concentration and diameter of Ag NWs with a thickness of 0.4 mm on microwave absorption are investigated.The results indicate that for an EVA-to-CB weight ratio of 1：3, Ag NW concentration of 1.0 mg/100 m L, and average diameter of 56 nm, the reflection loss（RL） of the composite is below-10 d B in a frequency range of 9.3 Ghz–18.0 GHz, with the minimum values of-40.0 d B and-25.6 d B at 13.5 GHz and 15.3 GHz, respectively. A finite element method（FEM）is used for calculating the RL of the composite. The calculated results are in agreement with the experimental data.展开更多
A bandwidth microwave second harmonic generator is successfully designed using composite right/left-handed non- linear transmission lines （CRLH NLTLs） in a GaAs monolithic microwave integrated circuit （MMIC） techn...A bandwidth microwave second harmonic generator is successfully designed using composite right/left-handed non- linear transmission lines （CRLH NLTLs） in a GaAs monolithic microwave integrated circuit （MMIC） technology. The structure parameters of CRLH NLTLs, e.g. host transmission line, rectangular spiral inductor, and nonlinear capacitor, have a great impact on the second harmonic performance enhancement in terms of second harmonic frequency, output power, and conversion efficiency. It has been experimentally demonstrated that the second harmonic frequency is deter- mined by the anomalous dispersion of CRLH NLTLs and can be significantly improved by effectively adjusting these structure parameters. A good agreement between the measured and simulated second harmonic performances of Ka-band CRLH NLTLs frequency multipliers is successfully achieved, which further validates the design approach of frequency multipliers on CRLH NLTLs and indicates the potentials of CRLH NLTLs in terms of the generation of microwave and millimeter-wave signal source.展开更多
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 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）.
基金Supported by the National Natural Science Foundation of China(51025208,61001026)the Program for Changjiang Scholars and Innovative Research Team in University and New Century Excellent Talents in Universities
文摘In order to achieve an easy fabrication and considerable directional orientation, we use a sedimentation method to prepare composites consisting of Fe Si Al flakes. The flakes are dispersed in hydroxylated acrylic resin solution in sonication and natural form into laminated composite samples. Then, the toroidal rings are made with the prepared laminated composite samples. Compared with random orientational Fe Si Al flakes in the composite, the complex permeability of laminated sample has been obviously improved when microwave frequency is below 4 GHz, especially for the imaginary part. A model is proposed to explain the formation reason of aligned Fe Si Al composite by this method. Damping factor（α） is calculated by the combination of the effective medium theory and Landau-Lifshitz-Gilbert equation, and the permeability of the samples is verified by these theories.
基金Supported by the National Natural Science Foundation of China under Grant No 10332020
文摘Carbonaceous nanomaterials such as carbon nanotubes （CNTs）, magnetic metal nanomaterials and semicon- ductor nanomaterials are superior candidates for microwave absorbers. Taking full advantage of the features of CNTs, nanophase cobalt and nanophase zinc oxide, whose main microwave absorption mechanisms are based on resistance loss, magnetic loss and dielectric loss, we fabricate CNT/Co and CNT/ZnO heterostructure nanocom- posites, respectively. By using the CNTs, CNT/Co nanocomposites and CNT/ZnO nanocomposites as nanofillers, composites with polyester as matrix are prepared by in situ polymerization, and their microwave absorption per- formance is studied. It is indicated that the synergetic effects of the physic properties of different components in nano-heterostructures result in greatly enhanced microwave absorption performance in a wide frequency range. The absorption peak is increased, the absorption bandwidth is broadened, and the maximum peak shifts to a lower frequency.
基金Project partly supported by the National Natural Science Foundation of China(Grant No.61275174)
文摘The composite that can absorb the high-performance electromagnetic（EM） wave is constructed into a sandwiched structure composed of carbon black（CB）/ethylene-vinyl acetate（EVA） and Ag naowires（Ag NWs）. The Ag NWs sandwiched between two CB/EVA layers are used to improve the absorption properties of composite. The effects of EVA-to-CB weight ratio, concentration and diameter of Ag NWs with a thickness of 0.4 mm on microwave absorption are investigated.The results indicate that for an EVA-to-CB weight ratio of 1：3, Ag NW concentration of 1.0 mg/100 m L, and average diameter of 56 nm, the reflection loss（RL） of the composite is below-10 d B in a frequency range of 9.3 Ghz–18.0 GHz, with the minimum values of-40.0 d B and-25.6 d B at 13.5 GHz and 15.3 GHz, respectively. A finite element method（FEM）is used for calculating the RL of the composite. The calculated results are in agreement with the experimental data.
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.61401373)the Research Fund for the Doctoral Program of Southwest University,China(Grant No.SWU111030)
文摘A bandwidth microwave second harmonic generator is successfully designed using composite right/left-handed non- linear transmission lines （CRLH NLTLs） in a GaAs monolithic microwave integrated circuit （MMIC） technology. The structure parameters of CRLH NLTLs, e.g. host transmission line, rectangular spiral inductor, and nonlinear capacitor, have a great impact on the second harmonic performance enhancement in terms of second harmonic frequency, output power, and conversion efficiency. It has been experimentally demonstrated that the second harmonic frequency is deter- mined by the anomalous dispersion of CRLH NLTLs and can be significantly improved by effectively adjusting these structure parameters. A good agreement between the measured and simulated second harmonic performances of Ka-band CRLH NLTLs frequency multipliers is successfully achieved, which further validates the design approach of frequency multipliers on CRLH NLTLs and indicates the potentials of CRLH NLTLs in terms of the generation of microwave and millimeter-wave signal source.
