Polarization feature is one of the important features of radar targets,which has been used in many fields.In this paper,the grid models of some typical foreign moving targets are constructed on the simulation platform...Polarization feature is one of the important features of radar targets,which has been used in many fields.In this paper,the grid models of some typical foreign moving targets are constructed on the simulation platform,such as glider,cruiser,fixed wing aircraft,and rotorcraft.The electromagnetic scattering characteristics of the moving platforms under the incidence of circular polarization waves are calculated.The typical polarization characteristics which the orthogonal and in-phase components have in the echoes are analyzed and proved.Based on the polarization scattering matrix(PSM)theory,from the point of view of the physical reproduction,the technical status quo that the existing technical approaches are difficult to realize the passive simulation of polarization characteristic of the target is summarized.To solve this problem,combined with the vector synthesis law,the realization mechanism of controllable polarization characteristic of target echoes is proposed,the analytical expressions of polarization control matrix and polarization ratio are deduced,and the controllability of polarization ratio feature in the case of circular polarization is verified by simulation calculation.展开更多
An efficient and real-time simulation method is proposed for the dynamic electromagnetic characteristics of cluster targets to meet the requirements of engineering practical applications.First,the coordinate transform...An efficient and real-time simulation method is proposed for the dynamic electromagnetic characteristics of cluster targets to meet the requirements of engineering practical applications.First,the coordinate transformation method is used to establish a geometric model of the observation scene,which is described by the azimuth angles and elevation angles of the radar in the target reference frame and the attitude angles of the target in the radar reference frame.Then,an approach for dynamic electromagnetic scattering simulation is proposed.Finally,a fast-computing method based on sparsity in the time domain,space domain,and frequency domain is proposed.The method analyzes the sparsity-based dynamic scattering characteristic of the typical cluster targets.The error between the sparsity-based method and the benchmark is small,proving the effectiveness of the proposed method.展开更多
Conductive hydrogels have potential applications in shielding electromagnetic(EM)radiation interference in deformable and wearable electronic devices,but usually suffer from poor environmental stability and stretching...Conductive hydrogels have potential applications in shielding electromagnetic(EM)radiation interference in deformable and wearable electronic devices,but usually suffer from poor environmental stability and stretching-induced shielding performance degradation.Although organohydrogels can improve the environmental stability of materials,their development is at the expense of reducing electrical conductivity and thus weakening EM interference shielding ability.Here,a MXene organohydrogel is prepared which is composed of MXene network for electron conduction,binary solvent channels for ion conduction,and abundant solvent-polymer-MXene interfaces for EM wave scattering.This organohydrogel possesses excellent anti-drying ability,low-temperature tolerance,stretchability,shape adaptability,adhesion and rapid self-healing ability.Two effective strategies have been proposed to solve the problems of current organohydrogel shielding materials.By reasonably controlling the MXene content and the glycerol-water ratio in the gel,MXene organohydrogel can exhibit exceptionally enhanced EM interference shielding performances compared to MXene hydrogel due to the increased physical cross-linking density of the gel.Moreover,MXene organohydrogel shows attractive stretching-enhanced interference effectiveness,caused by the connection and parallel arrangement of MXene nanosheets.This well-designed MXene organohydrogel has potential applications in shielding EM interference in deformable and wearable electronic devices.展开更多
For composite electromagnetic(EM)scattering from rough surface and target above it in near-field condition,modified shooting and bouncing ray(SBR)method and integral equation method(IEM),which are analytic methods com...For composite electromagnetic(EM)scattering from rough surface and target above it in near-field condition,modified shooting and bouncing ray(SBR)method and integral equation method(IEM),which are analytic methods combined with two-scale model for rough surface,are proposed to solve the composite near-field scattering problems.And the modified method is verified in effectiveness and accuracy by comparing the simulation results with measured results.Finally,the composite near-fielding scattering characteristics of a slanted plane and rough water surface below are obtained by using the proposed methods,and the dynamic tendency of composite scattering characteristics versus near-fielding distance is analyzed,which may have practical contribution to engineering programs in need of radar targets near-field characteristics under extra-low-altitude conditions.展开更多
The exact radar cross-section(RCS) measurement is difficult when the scattering of targets is low. Full polarimetric calibration is one technique that offers the potential for improving the accuracy of RCS measurement...The exact radar cross-section(RCS) measurement is difficult when the scattering of targets is low. Full polarimetric calibration is one technique that offers the potential for improving the accuracy of RCS measurements. There are numerous polarimetric calibration algorithms. Some complex expressions in these algorithms cannot be easily used in an engineering practice. A radar polarimetric coefficients matrix(RPCM) with a simpler expression is presented for the monostatic radar polarization scattering matrix(PSM) measurement. Using a rhombic dihedral corner reflector and a metallic sphere, the RPCM can be obtained by solving a set of equations, which can be used to find the true PSM for any target. An example for the PSM of a metallic dish shows that the proposed method obviously improves the accuracy of crosspolarized RCS measurements.展开更多
THz Radar Cross Section(RCS)measurement setup based on THz Time Domain Spectroscopy(TDS)is built to provide large scaled targets test ability in recent years.As calibrations,the metal plates and dihedrons are used in ...THz Radar Cross Section(RCS)measurement setup based on THz Time Domain Spectroscopy(TDS)is built to provide large scaled targets test ability in recent years.As calibrations,the metal plates and dihedrons are used in our experiments.The measurements are performed in a monostatic terahertz time-domain setup.The author proposed time domain and frequency domain calibration methods for angular RCS of calibrations,comparing the measurements with the theory to verify the ability of the time domain measurement setup.展开更多
The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third...The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third dimensionality recognition.In this paper,combined with the actual triple star orbits,a sparse flight spaceborne SAR 3-D imaging method based on the sparse spectrum of interferometry and the principal component analysis(PCA)is presented.Firstly,interferometric processing is utilized to reach an effective sparse representation of radar images in the frequency domain.Secondly,as a method with simple principle and fast calculation,the PCA is introduced to extract the main features of the image spectrum according to its principal characteristics.Finally,the 3-D image can be obtained by inverse transformation of the reconstructed spectrum by the PCA.The simulation results of 4.84 km equivalent cross-track aperture and corresponding 1.78 m cross-track resolution verify the effective suppression of this method on high-frequency sidelobe noise introduced by sparse flight with a sparsity of 49%and random noise introduced by the receiver.Meanwhile,due to the influence of orbit distribution of the actual triple star orbits,the simulation results of the sparse flight with the 7-bit Barker code orbits are given as a comparison and reference to illuminate the significance of orbit distribution for this reconstruction results.This method has prospects for sparse flight 3-D imaging in high latitude areas for its short revisit period.展开更多
In airborne array synthetic aperture radar(SAR), the three-dimensional(3D) imaging performance and cross-track resolution depends on the length of the equivalent array. In this paper, Barker sequence criterion is used...In airborne array synthetic aperture radar(SAR), the three-dimensional(3D) imaging performance and cross-track resolution depends on the length of the equivalent array. In this paper, Barker sequence criterion is used for sparse flight sampling of airborne array SAR, in order to obtain high cross-track resolution in as few times of flights as possible. Under each flight, the imaging algorithm of back projection(BP) and the data extraction method based on modified uniformly redundant arrays(MURAs) are utilized to obtain complex 3D image pairs. To solve the side-lobe noise in images, the interferometry between each image pair is implemented, and compressed sensing(CS) reconstruction is adopted in the frequency domain. Furthermore, to restore the geometrical relationship between each flight, the phase information corresponding to negative MURA is compensated on each single-pass image reconstructed by CS. Finally,by coherent accumulation of each complex image, the high resolution in cross-track direction is obtained. Simulations and experiments in X-band verify the availability.展开更多
To handle the electromagnetic problems of the bi-static radar cross section(RCS) calculation of scatterer in a wide frequency band, a finite-difference time-domain(FDTD) extrapolation method combining with discrete Fo...To handle the electromagnetic problems of the bi-static radar cross section(RCS) calculation of scatterer in a wide frequency band, a finite-difference time-domain(FDTD) extrapolation method combining with discrete Fourier transform(DFT) is proposed. By comparing the formulas between the steady state field extrapolation method and the transient field extrapolation method,a novel extrapolation method combining with DFT used in FDTD is proposed when a transient field incident wave is introduced. With the proposed method, the full-angle RCS distribution in a wide frequency band can be achieved through one-time FDTD calculation.Afterwards, the back-scattering RCS distributions of a double olive body and a sphere-cone body are calculated. Numerical results verify the validity of the proposed method.展开更多
在一张二维的摇的小粒的床上沉浸的一个入侵者的动态行为试验性地被调查。与背景粒子的二种类型，描绘入侵者的运动的 f 阶段图被测量并且比较。甚至与一样的尺寸和到背景粒子的入侵者的密度比率，入侵者以给定的震动的条件展出不同行...在一张二维的摇的小粒的床上沉浸的一个入侵者的动态行为试验性地被调查。与背景粒子的二种类型，描绘入侵者的运动的 f 阶段图被测量并且比较。甚至与一样的尺寸和到背景粒子的入侵者的密度比率，入侵者以给定的震动的条件展出不同行为，这被发现：在一张小粒的床上的升起的行为；在另一张小粒的床上的下沉行为。我们稍微调节尺寸和密度比率证实试验性的结果的可靠性。另外，我们在入侵者的运动上检验空隙的空气，传送对流和起始的位置的影响，推测相反的运动能被跟踪到背景粒子的材料性质。展开更多
An analytical variational method for the ground state of the biased quantum Rabi model in the ultra-strong coupling regime is presented. This analytical variational method can be obtained by a unitary transformation o...An analytical variational method for the ground state of the biased quantum Rabi model in the ultra-strong coupling regime is presented. This analytical variational method can be obtained by a unitary transformation or alternatively by assuming the form of the ground state wave function. The key of the method is to introduce a variational parameter λ,which can be determined by minimizing the energy functional. Using this method, we calculate the physical observables with high accuracy in comparison with the numerical exact ones. Our method evidently improves over the widely used general rotating-wave approximation(GRWA) in both qualitative and quantitative aspects.展开更多
Corresponding to the atmospheric transmission windows of the electromagnetic spectrum in the low terahertz range,the mode coupling and dispersion characteristics of two helically corrugated waveguides(HCW)in the frequ...Corresponding to the atmospheric transmission windows of the electromagnetic spectrum in the low terahertz range,the mode coupling and dispersion characteristics of two helically corrugated waveguides(HCW)in the frequency ranges of 90 GHz-100 GHz and 260 GHz-265 GHz are studied.Through analytic calculations and numerical simulations,dispersion curves and structural parameters of the two frequency ranges waveguides are obtained.A novel method was proposed to obtain the dispersion of the HCW from the eigenwave solution using a periodic boundary condition.The HCW in a frequency range of 90 GHz-100 GHz was fabricated and its dispersion performance was measured.By comparing the measured results with the theoretical and the simulated results,the validity of the analytical and simulation method is verified.Limited to our machining capability,the dispersion of the 260 GHz-265 GHz HCW was only simulated and calculated and it was found that the results agree well with each other.展开更多
Vertically vibrated segregation behaviors of binary granular mixtures with different interstitial media are experimentally investigated.To study the role of interstitial media on the segregation,two types of interstit...Vertically vibrated segregation behaviors of binary granular mixtures with different interstitial media are experimentally investigated.To study the role of interstitial media on the segregation,two types of interstitial fluids are adopted and the resulting phase diagrams are compared.The water-immersed granular mixture exhibits two kinds of complete segregation behaviors:Brazil nut effect and sandwich patterns,at least the latter is absent in the same air-immersed mixture.Additionally,the segregation extent is improved remarkably for the water-immersed mixture.The experimental observation further confirms that the effect of interstitial media on the relative motion of grains is one of the predominant mechanisms for granular segregation.展开更多
The investigation on quantum radar requires accurate computation of the state vectors of the single-photon processes of the two-level system in free space. However, the traditional Weisskopf-Wigner(W-W) theory fails t...The investigation on quantum radar requires accurate computation of the state vectors of the single-photon processes of the two-level system in free space. However, the traditional Weisskopf-Wigner(W-W) theory fails to deal with those processes other than spontaneous emission. To solve this problem, we provide a new method based on the renormalization theory. We evaluate the renormalized time-ordered Green functions associated with the single-photon processes, and relate them to the corresponding state vectors. It is found that the ultraviolet divergences generated by the Lamb shift and higher-order interactions can be systematically subtracted in the state vectors. The discussions on spontaneous emission and single-photon absorption are then presented to illustrate the proposed method. For spontaneous emission, we obtain the same results of the W-W theory. For single-photon absorption where W-W theory fails, we find that the two-level electric dipole first gets excited rapidly and then decays exponentially, and that the efficiency of the single-photon absorption declines as the bandwidth of the incident photon becomes narrow. The proposed method can improve the investigation on quantum radar.展开更多
We illustrate that three identical nanocylinders self-assembled into a trimer with a small interparticle gap separation support strong Fano-like interference.The asymmetry line shape of the Fano-like resonance can be ...We illustrate that three identical nanocylinders self-assembled into a trimer with a small interparticle gap separation support strong Fano-like interference.The asymmetry line shape of the Fano-like resonance can be controlled by modifying the cluster structures,and a narrow linewidth between a peak and a dip is displayed in the line trimer.The resonant behaviors of the trimers could be strengthened by increasing the permittivity of the nanorods,and the asymmetry resonance is highly sensitive to the angle of the incident wave due to the orientation-dependent coupling between the cylinders in the cluster.The present study provides a way to investigate the environmental change caused by the reshaped asymmetry line,which can be applied to future high-performance resonance sensors.展开更多
The terahertz radiations generated through a slab of GaAs-based photoconductive antennas are calculated from the nonlinear model and measured by a time domain spectroscopy system.The calculated spectra for the differe...The terahertz radiations generated through a slab of GaAs-based photoconductive antennas are calculated from the nonlinear model and measured by a time domain spectroscopy system.The calculated spectra for the different pulses are in agreement with our experimental observations.This consistency suggests that the description of the nonlinear model captures the basic features of this photoelectrical terahertz emission mechanism.Furthermore,1/f background noise dominates the terahertz detection in our experiments when the frequency is larger than 3 THz.展开更多
Metal-organic framework materials(MOFs)have been widely stu-died because of their adjustable composition and controllable structure in the field of microwave absorption(MA).Therein,Prussian blue analogs(PBA)have attra...Metal-organic framework materials(MOFs)have been widely stu-died because of their adjustable composition and controllable structure in the field of microwave absorption(MA).Therein,Prussian blue analogs(PBA)have attracted the attention of researchers with ultra-high metal content.However,the attenua-tion ability of microwave for PBA-based composites is still unsatis-factory up to now.Therefore,the NiFe/CoFe@C composites were prepared by carbonizing polymetallic PBA(NiCoFe PBA)materials in this work,and the influence of different metal alloy components on MA was explored by adjusting the ratio of metal ions(Ni^(2+)/Co^(2+)).Moreover,the NiFe/CoFe@C composites have rich interfaces and enhance the polarization loss due to the introduction of Ni and it has an optimal performance at 2.7 mm that is the reflection loss(RL)is−41.49 dB and an effective absorption bandwidth(EAB)is 7.12 GHz with 1/1(Ni^(2+)/Co^(2+)).The above data provides a research idea for obtaining light and efficient absorbers.展开更多
We explore the tricritical points and the critical lines of both Blume Emery Griffiths and Ising model within long-range interactions in the microcanonical ensemble.For K = Kmtp,the tricritical exponents take the val...We explore the tricritical points and the critical lines of both Blume Emery Griffiths and Ising model within long-range interactions in the microcanonical ensemble.For K = Kmtp,the tricritical exponents take the valuesβ = 1/4,1 =γ^-≠γ^+ = 1/2 and 0 =α^-≠α^+ =-1/2,which disagree with classical(mean ffeld) values.When K > Kmtp,the phase transition becomes second order and the critical exponents have classical values except close to the canonical tricritical parameters(Kctp),where the values of the critical expoents become β = 1/2,1 = γ^-≠γ^+= 2and 0 =α^-≠α^+ = 1.展开更多
The density of states of long-range Blume-Emery-Griffiths(BEG) and short-range Ising models are obtained by using Wang-Landau sampling with adaptive windows in energy and magnetization space.With accurate density of s...The density of states of long-range Blume-Emery-Griffiths(BEG) and short-range Ising models are obtained by using Wang-Landau sampling with adaptive windows in energy and magnetization space.With accurate density of states,we are able to calculate the microcanonical specific heat of fixed magnetization introduced by Kastner et al.in the regions of positive and negative temperature.The microcanonical phase diagram of the Ising model shows a continuous phase transition at a negative temperature in energy and magnetization plane.However the phase diagram of the long-range model constructed by peaks of the microcanonical specific heat looks obviously different from the Ising chart.展开更多
In order to design the scale model in a wide frequency range,a method based on the reflective loss is proposed according to the high-frequency approximation algorithm,and an example of designing the scale model of a p...In order to design the scale model in a wide frequency range,a method based on the reflective loss is proposed according to the high-frequency approximation algorithm,and an example of designing the scale model of a plate-shaped absorber is given in this paper.In the example,the frequency of the full-size measurement ranges from 2.0 GHz to 2.4 GHz,the thickness of the full-size absorber is 1 mm and the scale ratio is 1/5.A two-layer scale absorber is obtained by the proposed method.The thickness values of the bottom and top layer are 0.4 mm and 0.5 mm,respectively.Furthermore,the scattering properties of a plate model and an SLICY model are studied by FEKO to verify the effectiveness of the designed scale absorber.Compared with the corresponding values from the theoretical scale model,the average values of the absolute deviations in 10 GHz^12 GHz are 0.53 d Bm^2,0.65 d Bm^2,0.76 d Bm^2 for the plate model and 0.20 d Bm^2,0.95 d Bm^2,0.77 d Bm^2 for the SLICY model while the incident angles are 0?,30?,and 60?,respectively.These deviations fall within the Radar cross section(RCS) measurement tolerance.Thus,the work in this paper has important theoretical and practical significance.展开更多
基金supported by the National Natural Science Foundation of China(11927803A020414).
文摘Polarization feature is one of the important features of radar targets,which has been used in many fields.In this paper,the grid models of some typical foreign moving targets are constructed on the simulation platform,such as glider,cruiser,fixed wing aircraft,and rotorcraft.The electromagnetic scattering characteristics of the moving platforms under the incidence of circular polarization waves are calculated.The typical polarization characteristics which the orthogonal and in-phase components have in the echoes are analyzed and proved.Based on the polarization scattering matrix(PSM)theory,from the point of view of the physical reproduction,the technical status quo that the existing technical approaches are difficult to realize the passive simulation of polarization characteristic of the target is summarized.To solve this problem,combined with the vector synthesis law,the realization mechanism of controllable polarization characteristic of target echoes is proposed,the analytical expressions of polarization control matrix and polarization ratio are deduced,and the controllability of polarization ratio feature in the case of circular polarization is verified by simulation calculation.
文摘An efficient and real-time simulation method is proposed for the dynamic electromagnetic characteristics of cluster targets to meet the requirements of engineering practical applications.First,the coordinate transformation method is used to establish a geometric model of the observation scene,which is described by the azimuth angles and elevation angles of the radar in the target reference frame and the attitude angles of the target in the radar reference frame.Then,an approach for dynamic electromagnetic scattering simulation is proposed.Finally,a fast-computing method based on sparsity in the time domain,space domain,and frequency domain is proposed.The method analyzes the sparsity-based dynamic scattering characteristic of the typical cluster targets.The error between the sparsity-based method and the benchmark is small,proving the effectiveness of the proposed method.
基金This work was financially supported by Beijing Natural Science Foundation(2212033)National Natural Science Foundation of China(51971008,U1832138,51731002 and 51671010)+1 种基金the Fundamental Research Funds for the Central UniversitiesOpen access funding provided by Shanghai Jiao Tong University
文摘Conductive hydrogels have potential applications in shielding electromagnetic(EM)radiation interference in deformable and wearable electronic devices,but usually suffer from poor environmental stability and stretching-induced shielding performance degradation.Although organohydrogels can improve the environmental stability of materials,their development is at the expense of reducing electrical conductivity and thus weakening EM interference shielding ability.Here,a MXene organohydrogel is prepared which is composed of MXene network for electron conduction,binary solvent channels for ion conduction,and abundant solvent-polymer-MXene interfaces for EM wave scattering.This organohydrogel possesses excellent anti-drying ability,low-temperature tolerance,stretchability,shape adaptability,adhesion and rapid self-healing ability.Two effective strategies have been proposed to solve the problems of current organohydrogel shielding materials.By reasonably controlling the MXene content and the glycerol-water ratio in the gel,MXene organohydrogel can exhibit exceptionally enhanced EM interference shielding performances compared to MXene hydrogel due to the increased physical cross-linking density of the gel.Moreover,MXene organohydrogel shows attractive stretching-enhanced interference effectiveness,caused by the connection and parallel arrangement of MXene nanosheets.This well-designed MXene organohydrogel has potential applications in shielding EM interference in deformable and wearable electronic devices.
基金Project supported by the National Natural Science Foundation of China(Grant No.61372033).
文摘For composite electromagnetic(EM)scattering from rough surface and target above it in near-field condition,modified shooting and bouncing ray(SBR)method and integral equation method(IEM),which are analytic methods combined with two-scale model for rough surface,are proposed to solve the composite near-field scattering problems.And the modified method is verified in effectiveness and accuracy by comparing the simulation results with measured results.Finally,the composite near-fielding scattering characteristics of a slanted plane and rough water surface below are obtained by using the proposed methods,and the dynamic tendency of composite scattering characteristics versus near-fielding distance is analyzed,which may have practical contribution to engineering programs in need of radar targets near-field characteristics under extra-low-altitude conditions.
基金supported by the National Basic Research Program of China(973 Program)(2010CB731905)
文摘The exact radar cross-section(RCS) measurement is difficult when the scattering of targets is low. Full polarimetric calibration is one technique that offers the potential for improving the accuracy of RCS measurements. There are numerous polarimetric calibration algorithms. Some complex expressions in these algorithms cannot be easily used in an engineering practice. A radar polarimetric coefficients matrix(RPCM) with a simpler expression is presented for the monostatic radar polarization scattering matrix(PSM) measurement. Using a rhombic dihedral corner reflector and a metallic sphere, the RPCM can be obtained by solving a set of equations, which can be used to find the true PSM for any target. An example for the PSM of a metallic dish shows that the proposed method obviously improves the accuracy of crosspolarized RCS measurements.
基金The Science and Technology Commission of Shanghai Municipality under Grant(16ZR1435000)
文摘THz Radar Cross Section(RCS)measurement setup based on THz Time Domain Spectroscopy(TDS)is built to provide large scaled targets test ability in recent years.As calibrations,the metal plates and dihedrons are used in our experiments.The measurements are performed in a monostatic terahertz time-domain setup.The author proposed time domain and frequency domain calibration methods for angular RCS of calibrations,comparing the measurements with the theory to verify the ability of the time domain measurement setup.
基金This work was supported by the General Design Department,China Academy of Space Technology(10377).
文摘The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third dimensionality recognition.In this paper,combined with the actual triple star orbits,a sparse flight spaceborne SAR 3-D imaging method based on the sparse spectrum of interferometry and the principal component analysis(PCA)is presented.Firstly,interferometric processing is utilized to reach an effective sparse representation of radar images in the frequency domain.Secondly,as a method with simple principle and fast calculation,the PCA is introduced to extract the main features of the image spectrum according to its principal characteristics.Finally,the 3-D image can be obtained by inverse transformation of the reconstructed spectrum by the PCA.The simulation results of 4.84 km equivalent cross-track aperture and corresponding 1.78 m cross-track resolution verify the effective suppression of this method on high-frequency sidelobe noise introduced by sparse flight with a sparsity of 49%and random noise introduced by the receiver.Meanwhile,due to the influence of orbit distribution of the actual triple star orbits,the simulation results of the sparse flight with the 7-bit Barker code orbits are given as a comparison and reference to illuminate the significance of orbit distribution for this reconstruction results.This method has prospects for sparse flight 3-D imaging in high latitude areas for its short revisit period.
文摘In airborne array synthetic aperture radar(SAR), the three-dimensional(3D) imaging performance and cross-track resolution depends on the length of the equivalent array. In this paper, Barker sequence criterion is used for sparse flight sampling of airborne array SAR, in order to obtain high cross-track resolution in as few times of flights as possible. Under each flight, the imaging algorithm of back projection(BP) and the data extraction method based on modified uniformly redundant arrays(MURAs) are utilized to obtain complex 3D image pairs. To solve the side-lobe noise in images, the interferometry between each image pair is implemented, and compressed sensing(CS) reconstruction is adopted in the frequency domain. Furthermore, to restore the geometrical relationship between each flight, the phase information corresponding to negative MURA is compensated on each single-pass image reconstructed by CS. Finally,by coherent accumulation of each complex image, the high resolution in cross-track direction is obtained. Simulations and experiments in X-band verify the availability.
基金supported by the National Natural Science Foundation of China(61401361)the Fundamental Research Funds for the Central Universities of China(31020150104)
文摘To handle the electromagnetic problems of the bi-static radar cross section(RCS) calculation of scatterer in a wide frequency band, a finite-difference time-domain(FDTD) extrapolation method combining with discrete Fourier transform(DFT) is proposed. By comparing the formulas between the steady state field extrapolation method and the transient field extrapolation method,a novel extrapolation method combining with DFT used in FDTD is proposed when a transient field incident wave is introduced. With the proposed method, the full-angle RCS distribution in a wide frequency band can be achieved through one-time FDTD calculation.Afterwards, the back-scattering RCS distributions of a double olive body and a sphere-cone body are calculated. Numerical results verify the validity of the proposed method.
基金Supported by the National Natural Science Foundation of China under Grant No 11104013.
文摘在一张二维的摇的小粒的床上沉浸的一个入侵者的动态行为试验性地被调查。与背景粒子的二种类型，描绘入侵者的运动的 f 阶段图被测量并且比较。甚至与一样的尺寸和到背景粒子的入侵者的密度比率，入侵者以给定的震动的条件展出不同行为，这被发现：在一张小粒的床上的升起的行为；在另一张小粒的床上的下沉行为。我们稍微调节尺寸和密度比率证实试验性的结果的可靠性。另外，我们在入侵者的运动上检验空隙的空气，传送对流和起始的位置的影响，推测相反的运动能被跟踪到背景粒子的材料性质。
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674139,11604009,and 11704025)the Program for Changjiang Scholars and Innovative Research Team in University,China(Grant No.IRT-16R35)+1 种基金the Fundamental Research Funds for the Central Universities,Chinathe financial support of the Future and Emerging Technologies(FET)programme within the Seventh Framework Programme for Research of the European Commission,under FET-Open Grant No.618083(CNTQC)
文摘An analytical variational method for the ground state of the biased quantum Rabi model in the ultra-strong coupling regime is presented. This analytical variational method can be obtained by a unitary transformation or alternatively by assuming the form of the ground state wave function. The key of the method is to introduce a variational parameter λ,which can be determined by minimizing the energy functional. Using this method, we calculate the physical observables with high accuracy in comparison with the numerical exact ones. Our method evidently improves over the widely used general rotating-wave approximation(GRWA) in both qualitative and quantitative aspects.
文摘Corresponding to the atmospheric transmission windows of the electromagnetic spectrum in the low terahertz range,the mode coupling and dispersion characteristics of two helically corrugated waveguides(HCW)in the frequency ranges of 90 GHz-100 GHz and 260 GHz-265 GHz are studied.Through analytic calculations and numerical simulations,dispersion curves and structural parameters of the two frequency ranges waveguides are obtained.A novel method was proposed to obtain the dispersion of the HCW from the eigenwave solution using a periodic boundary condition.The HCW in a frequency range of 90 GHz-100 GHz was fabricated and its dispersion performance was measured.By comparing the measured results with the theoretical and the simulated results,the validity of the analytical and simulation method is verified.Limited to our machining capability,the dispersion of the 260 GHz-265 GHz HCW was only simulated and calculated and it was found that the results agree well with each other.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11104013 and 10975014Excellent Young Scholars Research Fund of Beijing Institute of Technology.
文摘Vertically vibrated segregation behaviors of binary granular mixtures with different interstitial media are experimentally investigated.To study the role of interstitial media on the segregation,two types of interstitial fluids are adopted and the resulting phase diagrams are compared.The water-immersed granular mixture exhibits two kinds of complete segregation behaviors:Brazil nut effect and sandwich patterns,at least the latter is absent in the same air-immersed mixture.Additionally,the segregation extent is improved remarkably for the water-immersed mixture.The experimental observation further confirms that the effect of interstitial media on the relative motion of grains is one of the predominant mechanisms for granular segregation.
基金supported by the National Natural Science Foundation of China (6149690025)。
文摘The investigation on quantum radar requires accurate computation of the state vectors of the single-photon processes of the two-level system in free space. However, the traditional Weisskopf-Wigner(W-W) theory fails to deal with those processes other than spontaneous emission. To solve this problem, we provide a new method based on the renormalization theory. We evaluate the renormalized time-ordered Green functions associated with the single-photon processes, and relate them to the corresponding state vectors. It is found that the ultraviolet divergences generated by the Lamb shift and higher-order interactions can be systematically subtracted in the state vectors. The discussions on spontaneous emission and single-photon absorption are then presented to illustrate the proposed method. For spontaneous emission, we obtain the same results of the W-W theory. For single-photon absorption where W-W theory fails, we find that the two-level electric dipole first gets excited rapidly and then decays exponentially, and that the efficiency of the single-photon absorption declines as the bandwidth of the incident photon becomes narrow. The proposed method can improve the investigation on quantum radar.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11104013 and 10975014the Excellent Young Scholars Research Fund of the Beijing Institute of Technology.
文摘We illustrate that three identical nanocylinders self-assembled into a trimer with a small interparticle gap separation support strong Fano-like interference.The asymmetry line shape of the Fano-like resonance can be controlled by modifying the cluster structures,and a narrow linewidth between a peak and a dip is displayed in the line trimer.The resonant behaviors of the trimers could be strengthened by increasing the permittivity of the nanorods,and the asymmetry resonance is highly sensitive to the angle of the incident wave due to the orientation-dependent coupling between the cylinders in the cluster.The present study provides a way to investigate the environmental change caused by the reshaped asymmetry line,which can be applied to future high-performance resonance sensors.
基金Supported by the National Defense Research Foundation under Grant No 109750014.
文摘The terahertz radiations generated through a slab of GaAs-based photoconductive antennas are calculated from the nonlinear model and measured by a time domain spectroscopy system.The calculated spectra for the different pulses are in agreement with our experimental observations.This consistency suggests that the description of the nonlinear model captures the basic features of this photoelectrical terahertz emission mechanism.Furthermore,1/f background noise dominates the terahertz detection in our experiments when the frequency is larger than 3 THz.
基金This work was supported by the National Defense Technology Innovation Special Zone Spark Project[2016300TS00911901].
文摘Metal-organic framework materials(MOFs)have been widely stu-died because of their adjustable composition and controllable structure in the field of microwave absorption(MA).Therein,Prussian blue analogs(PBA)have attracted the attention of researchers with ultra-high metal content.However,the attenua-tion ability of microwave for PBA-based composites is still unsatis-factory up to now.Therefore,the NiFe/CoFe@C composites were prepared by carbonizing polymetallic PBA(NiCoFe PBA)materials in this work,and the influence of different metal alloy components on MA was explored by adjusting the ratio of metal ions(Ni^(2+)/Co^(2+)).Moreover,the NiFe/CoFe@C composites have rich interfaces and enhance the polarization loss due to the introduction of Ni and it has an optimal performance at 2.7 mm that is the reflection loss(RL)is−41.49 dB and an effective absorption bandwidth(EAB)is 7.12 GHz with 1/1(Ni^(2+)/Co^(2+)).The above data provides a research idea for obtaining light and efficient absorbers.
基金Supported by the National Natural Science Foundation of China under Grant No.11104032
文摘We explore the tricritical points and the critical lines of both Blume Emery Griffiths and Ising model within long-range interactions in the microcanonical ensemble.For K = Kmtp,the tricritical exponents take the valuesβ = 1/4,1 =γ^-≠γ^+ = 1/2 and 0 =α^-≠α^+ =-1/2,which disagree with classical(mean ffeld) values.When K > Kmtp,the phase transition becomes second order and the critical exponents have classical values except close to the canonical tricritical parameters(Kctp),where the values of the critical expoents become β = 1/2,1 = γ^-≠γ^+= 2and 0 =α^-≠α^+ = 1.
基金Supported by National Natural Science Foundation of China under Grant No.11104013Excellent Young Scholars Research Fund of Beijing Institute of Technology
文摘The density of states of long-range Blume-Emery-Griffiths(BEG) and short-range Ising models are obtained by using Wang-Landau sampling with adaptive windows in energy and magnetization space.With accurate density of states,we are able to calculate the microcanonical specific heat of fixed magnetization introduced by Kastner et al.in the regions of positive and negative temperature.The microcanonical phase diagram of the Ising model shows a continuous phase transition at a negative temperature in energy and magnetization plane.However the phase diagram of the long-range model constructed by peaks of the microcanonical specific heat looks obviously different from the Ising chart.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61601299 and 11404213)the Shanghai Municipal Science and Technology Commission,China(Grant Nos.17210730900 and 15ZR1439600)the Defense Industrial Technology,China(Grant No.B2120132001)
文摘In order to design the scale model in a wide frequency range,a method based on the reflective loss is proposed according to the high-frequency approximation algorithm,and an example of designing the scale model of a plate-shaped absorber is given in this paper.In the example,the frequency of the full-size measurement ranges from 2.0 GHz to 2.4 GHz,the thickness of the full-size absorber is 1 mm and the scale ratio is 1/5.A two-layer scale absorber is obtained by the proposed method.The thickness values of the bottom and top layer are 0.4 mm and 0.5 mm,respectively.Furthermore,the scattering properties of a plate model and an SLICY model are studied by FEKO to verify the effectiveness of the designed scale absorber.Compared with the corresponding values from the theoretical scale model,the average values of the absolute deviations in 10 GHz^12 GHz are 0.53 d Bm^2,0.65 d Bm^2,0.76 d Bm^2 for the plate model and 0.20 d Bm^2,0.95 d Bm^2,0.77 d Bm^2 for the SLICY model while the incident angles are 0?,30?,and 60?,respectively.These deviations fall within the Radar cross section(RCS) measurement tolerance.Thus,the work in this paper has important theoretical and practical significance.
