The electromagnetic parameters (permittivity and permeability) method,retrieved from the reflection and transmission coefficients of a slab,is presented.Improvements over existing methods,including the determination o...The electromagnetic parameters (permittivity and permeability) method,retrieved from the reflection and transmission coefficients of a slab,is presented.Improvements over existing methods,including the determination of the permittivity,permeability and impedance of the slab,are expressed as explicit functions of the S parameters for both the time-dependent factors,e^(iwt) and e^(-iwt) (ω is the angular frequency of the incident electromagnetic wave),and the proper selection of the sign of impedance and the real part of the refractive index.Moreover,based on the retrieving method,the calculations of the electromagnetic parameters of the conventional-material teflon slab standard sample through the experimental data of the S parameters are performed,which confirm the validity of the technique for the retrieval of electromagnetic parameters.展开更多
We report on the mechanism of the dielectric properties of oxygen vacancy in ZnO,using ab initio numerical simulations of oxygen vacancy on the band structure and dielectric properties,to develop photoelectric materia...We report on the mechanism of the dielectric properties of oxygen vacancy in ZnO,using ab initio numerical simulations of oxygen vacancy on the band structure and dielectric properties,to develop photoelectric material applications.It is revealed that the appearance of oxygen vacancies leads to wider energy band gap,obvious blue shift and increase in the peak of dielectric function as compared to the intrinsic ZnO simulation.We explain these unusual phenomena and analyze the dielectric changes with the mechanism of polarization in the semiconductors.It is shown that the main mechanism of influencing dielectric properties is the electron displacement polarization.The result may be helpful for development of photoelectric materials.展开更多
The high-temperature permittivity of quartz fibre-reinforced silicon dioxide (SiO2/SiO2 ) nano-composites is studied on the basis of the multi-scale theoretical model.We obtain the permittivity of the SiO2/SiO2 at hig...The high-temperature permittivity of quartz fibre-reinforced silicon dioxide (SiO2/SiO2 ) nano-composites is studied on the basis of the multi-scale theoretical model.We obtain the permittivity of the SiO2/SiO2 at high temperature,which is dependent on the temperature by data-mining.The result shows that the permittivity and loss tangent obtained by data-mining are well consistent with the measured ones.The high-temperature permittivity can be well predicted for SiO2/SiO2 by the as-proposed model and the data-mining method.展开更多
The first-principles numerical simulation is employed-to calculate the effect of replacement of carbon and silicon with boron on the electronic structure and optical properties of β-SiC.Mulliken analysis shows that t...The first-principles numerical simulation is employed-to calculate the effect of replacement of carbon and silicon with boron on the electronic structure and optical properties of β-SiC.Mulliken analysis shows that the B impurity bond lengths shrink in the case of Bsi,while they expand with reference to Bc.In addition,Bsi contains C-C,Si-Si and B-Si bonds.The calculated results show that the two systems of Bc and Bsi apply different dispersion.Bc is in accordance with the Lorentz dispersion theory while Bsi follows the Drude dispersion theory.Theoretic analysis and quantitative calculation are used for conductivity spectra in the infrared region.展开更多
The electronic properties of 3C-SiC doped with different contents of Ni are investigated by using first-principles calculations.It is observed that the non-filled impurity energy levels in the band-gap region increase...The electronic properties of 3C-SiC doped with different contents of Ni are investigated by using first-principles calculations.It is observed that the non-filled impurity energy levels in the band-gap region increase with increasing Ni content,which subsequently results in an enhancement of electrical conductivity of 3C-SiC.This enhancement in conductivity is verified by the conductivity spectrum in which new peaks appear in the middleinfrared region,visible region,and middle-ultraviolet region.It is further observed that the width and intensity of these newly appeared peaks increase with the increase of Ni content.The electronic density of states exhibits the peaks crossing the Fermi level,which favors the electronic transitions and proves Ni-doped 3C-SiC to be a half-metallic semiconductor.Through the analysis of electron density difference and Mulliken overlap population,it is found that the covalent bonds are formed between Ni and near-by C atoms.These features confirm that the Ni-doped 3C-SiC semiconductor is a promising material for device applications in modern day electronics.展开更多
An electron cyclotron maser based on anomalous Doppler effect(ADECM)with an initially axial beam velocity is considered,and the nonlinear equation of beam-wave interaction is presented.With the numerical methods,the n...An electron cyclotron maser based on anomalous Doppler effect(ADECM)with an initially axial beam velocity is considered,and the nonlinear equation of beam-wave interaction is presented.With the numerical methods,the nonlinear dynamics of the ADECM is investigated.It is shown that the saturated interaction efficiency of the ADECM approaches 90%and the interaction length for the saturated efficiency spans about 5–20 cm.The results may be of importance for designing a compact device in applications in microwave generations or microwave heating of ceramic laminates.展开更多
Bi_(0.95)_(0.05)FeO_(3)nanocrystals are synthesized by a hydrothermal method,and are crystallized in a rhombohedrally distorted perovskite BiFeO_(3)structure in the R3c space,with compressive lattice distortion induce...Bi_(0.95)_(0.05)FeO_(3)nanocrystals are synthesized by a hydrothermal method,and are crystallized in a rhombohedrally distorted perovskite BiFeO_(3)structure in the R3c space,with compressive lattice distortion induced by the Y substitution at Bi sites from XRD study Compared with BiFeO_(3)gained under similar conditions,the magnetic properties are greatly enhanced,with saturate magnetization of 2.3emu/g at room temperature.Microwave dielectric properties of Bi0.95 Y0.05FeO_(3)nanocrystals are investigated in the range of 2-18 GHz.The Y substitution results in the increase of permeability and decrease of permittivity which are attributed to the enhanced spin relaxation of domain wall motion and the weakened electron-relaxation caused by decreasing Fe^(2+),respectively.The changes for microwave dielectric response could lead to the excellent microwave absorption due to the improvement of the impedance match between BiFeO_(3)and air.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 51102007and 51132002the Fundamental Research Funds for the Central Universities of China under Grant No ZZ1131.
文摘The electromagnetic parameters (permittivity and permeability) method,retrieved from the reflection and transmission coefficients of a slab,is presented.Improvements over existing methods,including the determination of the permittivity,permeability and impedance of the slab,are expressed as explicit functions of the S parameters for both the time-dependent factors,e^(iwt) and e^(-iwt) (ω is the angular frequency of the incident electromagnetic wave),and the proper selection of the sign of impedance and the real part of the refractive index.Moreover,based on the retrieving method,the calculations of the electromagnetic parameters of the conventional-material teflon slab standard sample through the experimental data of the S parameters are performed,which confirm the validity of the technique for the retrieval of electromagnetic parameters.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50972014 and 50872159.
文摘We report on the mechanism of the dielectric properties of oxygen vacancy in ZnO,using ab initio numerical simulations of oxygen vacancy on the band structure and dielectric properties,to develop photoelectric material applications.It is revealed that the appearance of oxygen vacancies leads to wider energy band gap,obvious blue shift and increase in the peak of dielectric function as compared to the intrinsic ZnO simulation.We explain these unusual phenomena and analyze the dielectric changes with the mechanism of polarization in the semiconductors.It is shown that the main mechanism of influencing dielectric properties is the electron displacement polarization.The result may be helpful for development of photoelectric materials.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50872159,50972014,51072024 and 51132002.
文摘The high-temperature permittivity of quartz fibre-reinforced silicon dioxide (SiO2/SiO2 ) nano-composites is studied on the basis of the multi-scale theoretical model.We obtain the permittivity of the SiO2/SiO2 at high temperature,which is dependent on the temperature by data-mining.The result shows that the permittivity and loss tangent obtained by data-mining are well consistent with the measured ones.The high-temperature permittivity can be well predicted for SiO2/SiO2 by the as-proposed model and the data-mining method.
基金Supported by the State Key Program of the National Natural Science Foundation of China under Grant No 51132002the National Natural Science Foundation of China under Grant No 50972015the Natural Science Foundation of Hebei Province under Grant No A2011203026.
文摘The first-principles numerical simulation is employed-to calculate the effect of replacement of carbon and silicon with boron on the electronic structure and optical properties of β-SiC.Mulliken analysis shows that the B impurity bond lengths shrink in the case of Bsi,while they expand with reference to Bc.In addition,Bsi contains C-C,Si-Si and B-Si bonds.The calculated results show that the two systems of Bc and Bsi apply different dispersion.Bc is in accordance with the Lorentz dispersion theory while Bsi follows the Drude dispersion theory.Theoretic analysis and quantitative calculation are used for conductivity spectra in the infrared region.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50972015,51132002 and 51172026.
文摘The electronic properties of 3C-SiC doped with different contents of Ni are investigated by using first-principles calculations.It is observed that the non-filled impurity energy levels in the band-gap region increase with increasing Ni content,which subsequently results in an enhancement of electrical conductivity of 3C-SiC.This enhancement in conductivity is verified by the conductivity spectrum in which new peaks appear in the middleinfrared region,visible region,and middle-ultraviolet region.It is further observed that the width and intensity of these newly appeared peaks increase with the increase of Ni content.The electronic density of states exhibits the peaks crossing the Fermi level,which favors the electronic transitions and proves Ni-doped 3C-SiC to be a half-metallic semiconductor.Through the analysis of electron density difference and Mulliken overlap population,it is found that the covalent bonds are formed between Ni and near-by C atoms.These features confirm that the Ni-doped 3C-SiC semiconductor is a promising material for device applications in modern day electronics.
基金by the National Natural Science Foundation of China under Grant No 51102007the Fundamental Research Funds for the Central Universities of China under Grant No ZZ1131.
文摘An electron cyclotron maser based on anomalous Doppler effect(ADECM)with an initially axial beam velocity is considered,and the nonlinear equation of beam-wave interaction is presented.With the numerical methods,the nonlinear dynamics of the ADECM is investigated.It is shown that the saturated interaction efficiency of the ADECM approaches 90%and the interaction length for the saturated efficiency spans about 5–20 cm.The results may be of importance for designing a compact device in applications in microwave generations or microwave heating of ceramic laminates.
基金Supported by the National Natural Science Foundation of under Grant No 50872159,and the Physics Development Fund of BUCT.
文摘Bi_(0.95)_(0.05)FeO_(3)nanocrystals are synthesized by a hydrothermal method,and are crystallized in a rhombohedrally distorted perovskite BiFeO_(3)structure in the R3c space,with compressive lattice distortion induced by the Y substitution at Bi sites from XRD study Compared with BiFeO_(3)gained under similar conditions,the magnetic properties are greatly enhanced,with saturate magnetization of 2.3emu/g at room temperature.Microwave dielectric properties of Bi0.95 Y0.05FeO_(3)nanocrystals are investigated in the range of 2-18 GHz.The Y substitution results in the increase of permeability and decrease of permittivity which are attributed to the enhanced spin relaxation of domain wall motion and the weakened electron-relaxation caused by decreasing Fe^(2+),respectively.The changes for microwave dielectric response could lead to the excellent microwave absorption due to the improvement of the impedance match between BiFeO_(3)and air.
