Reducing the vibration transmission in beams is of significant interest,as beams are among the most widely used basic structures in numerous practical engineering applications.However,achieving broadband suppression o...Reducing the vibration transmission in beams is of significant interest,as beams are among the most widely used basic structures in numerous practical engineering applications.However,achieving broadband suppression of multi-polarization low-frequency vibration in beams presents a challenge.This study proposes a single-phase multi-resonant metabeam,which consists of a host beam with subwavelength arrays of tunable local resonators.These resonators exhibit adjustable multi-polarization resonant modes that strongly couple with the host beam,enabling simultaneous suppression of multi-type waves over a broad frequency range.The theoretical analysis demonstrates that under the fixed total added-mass ratio(γ_(total)=1.5),the tailored frequency spacing(δ=25-50 Hz)and the controlled loss factor(η=0.03–0.07)act synergistically to broaden bandgaps through resonant zone overlapping and attenuation peak smoothing.The experimental validation with monolithic three-dimensional(3D)-printed specimens confirms the efficacy of this design in multi-polarization vibration control within a deepsubwavelength bandgap,opening a new avenue for designing multi-polarization vibration suppression structures.展开更多
Carbon-based materials exhibit excellent dielectric absorption properties,among which graphene has received particular attention in research of electromagnetic wave absorbing materials because of its high electrical c...Carbon-based materials exhibit excellent dielectric absorption properties,among which graphene has received particular attention in research of electromagnetic wave absorbing materials because of its high electrical conductivity and unique large-area,thin-layer two-dimensional structural features.However,the electromagnetic absorption performance of the material is hindered from further improvement due to its single component composition.It is influenced by the conductive network of graphene,making it challenging to achieve a balance in impedance matching and electromagnetic loss,thereby restricting its broader application.To address these challenges,we developed a series of nickel hydroxide-modified graphene composites.Through a structural composite design,we optimized overall impedance matching,introduced diverse loss mechanisms to enhance electromagnetic loss performance,and utilized a secondary reaction control method to precisely regulate the deposition of nickel hydroxide on the graphene surface,thereby achieving regulate of the composite material's electromagnetic parameters within a defined range.Under low sample filling ratios and a thin sample thickness of 1.8 mm,the effective absorption bandwidth reaches 6.5 GHz,demonstrating excellent electromagnetic absorption performance.This study provides a controllable design approach for modulating material electromagnetic parameters by influencing the reaction process.It also offers a design method for composites with an outstanding electromagnetic loss mechanism.展开更多
The ice exceeding one million years old has significant meaning for verifying and interpreting the middle Pleistocene transition （MPT） and the relationship between greenhouse gas and climate change. The region near ...The ice exceeding one million years old has significant meaning for verifying and interpreting the middle Pleistocene transition （MPT） and the relationship between greenhouse gas and climate change. The region near Dome A in Antarctica satisfies the conditions for obtaining million-years-old ice since it has low temperatures and low accumulation rates. We analyze the corresponding relation between radar wave features and the crystal orientation fabric （COF） types based on the results of multi-polarization plane radio echo sounding （RES）. The results show that, even in the summit of the ice sheet, the COF type is not perfect, but is an elongated single-pole COF. Principal-axis-orientation differences of the COF among the different periods exist and reveal that the ice flow orientations are not constant but deviate clockwise with the increasing depth. This may be related to the adjacent basal valley or both height and position changes of the summit during the glacial-interglacial periods.展开更多
An improved algorithm for multi-polarization reconstruction from compact polarimetry （CP） is proposed. According to two fundamental assumptions in compact polarimetric reconstruction, two improvements are proposed. ...An improved algorithm for multi-polarization reconstruction from compact polarimetry （CP） is proposed. According to two fundamental assumptions in compact polarimetric reconstruction, two improvements are proposed. Firstly, the four-component model-based decomposition algorithm is modified with a new volume scattering model. The decomposed helix scattering component is then used to deal with the non-reflection symmetry condition in compact polarimetric measurements. Using the decomposed power and considering the scattering mechanism of each component, an average relationship between copolarized and crosspolarized channels is developed over the original polarization state extrapolation model. E-SAR polarimetric data acquired over the Oberpfaffenhofen area and JPL/AIRSAR polarimetric data acquired over San Francisco are used for verification, and good reconstruction results are obtained, demonstrating the effectiveness of the proposed algorithm.展开更多
A novel multi-layer planar antenna array to achieve multi-polarized radiation is developed. U-shaped coupling slots are embedded in the ground plane to extend the bandwidth. The phase relation between adjacent element...A novel multi-layer planar antenna array to achieve multi-polarized radiation is developed. U-shaped coupling slots are embedded in the ground plane to extend the bandwidth. The phase relation between adjacent elements in the radiation field is analyzed when adjacent elements are fed in opposite phase. Return loss and radiation pattern are measured for a 16-element antenna array at 12.5 GHz. The radiation pattern shows a good agreement with the calculated one in the shape of the main beam. The return-loss of the proposed antenna array is less than -20 dB in the 12.5 GHz frequency band （12.25-12.75 GHz）. Because of two feed ports the antenna can transmit arbitrary elliptic polarized waves if the two feed ports have different amplitude and phase. The main factors such as element spacing, substrate medium and manufacturing imperfection are analyzed and the corresponding conclusions are presented.展开更多
The development of 3D structural composites with electromagnetic(EM)wave absorption could attenuate EM waves.Herein,magnetized flower-like Cu_(9)S_(5)/ZnFe_(2)O_(4)composites were fabricated through a multistep hydrot...The development of 3D structural composites with electromagnetic(EM)wave absorption could attenuate EM waves.Herein,magnetized flower-like Cu_(9)S_(5)/ZnFe_(2)O_(4)composites were fabricated through a multistep hydrothermal method.The crystallographic and surface phase chemical information,morphological structure,and magnetic and EM parameters of the composites were analyzed.The prepared Cu_(9)S_(5)/ZnFe_(2)O_(4)composites have multiple loss paths for EM waves and present an overall 3D flower-like structure.The Cu_(9)S_(5)/ZnFe_(2)O_(4)composites exhibit a minimum reflection loss of-54.38 dB and a broad effective absorption bandwidth of 5.92 GHz.Through magnetization,ZnFe_(2)O_(4)particles are self-assembled and grown on the surfaces of Cu_(9)S_(5).Such a modification is conducive to the generation of additional cross-linking contact sites and the effective introduction of a large number of phase interfaces,crystalline defects,special three-dimensional flower-like structures,and magneto-electrical coupling loss effects.Moreover,the synergistic effect of multiple loss strategies effectively improves EM wave absorption by the material.This work can provide a strategy for the use of magnetizationmodified sulfide composite functional materials in EM wave absorption.展开更多
The multi-polar structure is a new international relationship structure, which differs greatly from both the bi-polar and uni-polar structures in both structure and nature, mainly emerging from the evolution of two as...The multi-polar structure is a new international relationship structure, which differs greatly from both the bi-polar and uni-polar structures in both structure and nature, mainly emerging from the evolution of two aspects： first, the meaning of ＂polar＂ has undergone a major change; and second, beyond the power structure, the relationship structure between nations is much different from the past and is inflicting an increasingly important impact on core implication of the multi-polar the structure. Decentralization is the structure. In the current reality of international politics, decentralization refers to the dissolution of US hegemony, as different nations and power centers are busy competing and cooperating with one another at different levels in accordance with their own advantages and characteristics. Globally, the multi-polar structure manifests a state in which the current power structure is loosening, while international relationships have become more diversified due to their ongoing development. This is the development of a new relationship structure that is of great significance and what calls for our closest attention.展开更多
The world is facing the third important global power shift.The United States,EU, Japan,Russia,China,and the newly emerging power group are becoming the six big forces in the international center stage,while the former...The world is facing the third important global power shift.The United States,EU, Japan,Russia,China,and the newly emerging power group are becoming the six big forces in the international center stage,while the former three forces and the latter three belong to two groups,waning and waxing respectively.The major shift in the global balance of power is bound to give rise to the transitional multi-polar configuration,which implies a shifting of leadership over the configuration,China and U.S.outweighing other forces,global issues looming large,homogeneity blending with heterogeneity,and a shifting center of world powers.The transitional multi-polar configuration is all about change,upon which China is one of the decisive forces.展开更多
The rapid development of microwave-terahertz frequency band technologies has created an urgent demand for broadband electromagnetic wave absorption materials.In this study,a heterostructured composite comprising mixed...The rapid development of microwave-terahertz frequency band technologies has created an urgent demand for broadband electromagnetic wave absorption materials.In this study,a heterostructured composite comprising mixed-phase 1T/2H-MoSe_(2)(002)and WO_(3)(200)nanosheets was constructed to realize efficient electromagnetic wave absorption and shielding across both microwave and terahertz frequency bands.In the microwave region,the 1T/2H-MoSe_(2)/WO_(3)absorber exhibits a minimum reflection loss of-66.62 dB at 14.98 GHz with a thickness of 1.77 mm,attributed to slow polarization relaxation induced by multiple interfaces and structural defects.In the terahertz range,the system delivers a dominant shielding effectiveness of 67.3 dB at 1.31 THz with a thickness of 2 mm.This performance arises from the precise alignment of the Fermi level of metallic 1T-MoSe_(2)with the conduction band of WO_(3)at the interface,enabling rapid electron injection into WO_(3)with oxygen vacancies via electrochromism.This process induces the transition from W(VI)–O to W(VI-)–O,thereby enhancing both electronic and ionic polarization losses.When incorporated into polyvinyl alcohol(PVA)and fabricated into films,the resulting 500-μm-thick(1T/2H-MoSe_(2))/WO_(3)/PVA composite film achieves a maximum shielding effectiveness of 71.51 dB in the 0.2–1.8 THz frequency range,demonstrating excellent practical applicability.展开更多
基金Project supported by the National Natural Science Foundation of China(No.51875569)。
文摘Reducing the vibration transmission in beams is of significant interest,as beams are among the most widely used basic structures in numerous practical engineering applications.However,achieving broadband suppression of multi-polarization low-frequency vibration in beams presents a challenge.This study proposes a single-phase multi-resonant metabeam,which consists of a host beam with subwavelength arrays of tunable local resonators.These resonators exhibit adjustable multi-polarization resonant modes that strongly couple with the host beam,enabling simultaneous suppression of multi-type waves over a broad frequency range.The theoretical analysis demonstrates that under the fixed total added-mass ratio(γ_(total)=1.5),the tailored frequency spacing(δ=25-50 Hz)and the controlled loss factor(η=0.03–0.07)act synergistically to broaden bandgaps through resonant zone overlapping and attenuation peak smoothing.The experimental validation with monolithic three-dimensional(3D)-printed specimens confirms the efficacy of this design in multi-polarization vibration control within a deepsubwavelength bandgap,opening a new avenue for designing multi-polarization vibration suppression structures.
基金supported by the Research Funds of the State Key Laboratory for Marine Corrosion and Protection(No.JS220903).
文摘Carbon-based materials exhibit excellent dielectric absorption properties,among which graphene has received particular attention in research of electromagnetic wave absorbing materials because of its high electrical conductivity and unique large-area,thin-layer two-dimensional structural features.However,the electromagnetic absorption performance of the material is hindered from further improvement due to its single component composition.It is influenced by the conductive network of graphene,making it challenging to achieve a balance in impedance matching and electromagnetic loss,thereby restricting its broader application.To address these challenges,we developed a series of nickel hydroxide-modified graphene composites.Through a structural composite design,we optimized overall impedance matching,introduced diverse loss mechanisms to enhance electromagnetic loss performance,and utilized a secondary reaction control method to precisely regulate the deposition of nickel hydroxide on the graphene surface,thereby achieving regulate of the composite material's electromagnetic parameters within a defined range.Under low sample filling ratios and a thin sample thickness of 1.8 mm,the effective absorption bandwidth reaches 6.5 GHz,demonstrating excellent electromagnetic absorption performance.This study provides a controllable design approach for modulating material electromagnetic parameters by influencing the reaction process.It also offers a design method for composites with an outstanding electromagnetic loss mechanism.
基金the National Natural Science Foundation of China(Grant No.40874060)the 863 projection(Grant No.2006AA09Z152)
文摘The ice exceeding one million years old has significant meaning for verifying and interpreting the middle Pleistocene transition （MPT） and the relationship between greenhouse gas and climate change. The region near Dome A in Antarctica satisfies the conditions for obtaining million-years-old ice since it has low temperatures and low accumulation rates. We analyze the corresponding relation between radar wave features and the crystal orientation fabric （COF） types based on the results of multi-polarization plane radio echo sounding （RES）. The results show that, even in the summit of the ice sheet, the COF type is not perfect, but is an elongated single-pole COF. Principal-axis-orientation differences of the COF among the different periods exist and reveal that the ice flow orientations are not constant but deviate clockwise with the increasing depth. This may be related to the adjacent basal valley or both height and position changes of the summit during the glacial-interglacial periods.
基金supported by the National Natural Science Foundation of China(41171317)the State Key Program of the Natural Science Foundation of China(61132008)the Research Foundation of Tsinghua University
文摘An improved algorithm for multi-polarization reconstruction from compact polarimetry （CP） is proposed. According to two fundamental assumptions in compact polarimetric reconstruction, two improvements are proposed. Firstly, the four-component model-based decomposition algorithm is modified with a new volume scattering model. The decomposed helix scattering component is then used to deal with the non-reflection symmetry condition in compact polarimetric measurements. Using the decomposed power and considering the scattering mechanism of each component, an average relationship between copolarized and crosspolarized channels is developed over the original polarization state extrapolation model. E-SAR polarimetric data acquired over the Oberpfaffenhofen area and JPL/AIRSAR polarimetric data acquired over San Francisco are used for verification, and good reconstruction results are obtained, demonstrating the effectiveness of the proposed algorithm.
文摘A novel multi-layer planar antenna array to achieve multi-polarized radiation is developed. U-shaped coupling slots are embedded in the ground plane to extend the bandwidth. The phase relation between adjacent elements in the radiation field is analyzed when adjacent elements are fed in opposite phase. Return loss and radiation pattern are measured for a 16-element antenna array at 12.5 GHz. The radiation pattern shows a good agreement with the calculated one in the shape of the main beam. The return-loss of the proposed antenna array is less than -20 dB in the 12.5 GHz frequency band （12.25-12.75 GHz）. Because of two feed ports the antenna can transmit arbitrary elliptic polarized waves if the two feed ports have different amplitude and phase. The main factors such as element spacing, substrate medium and manufacturing imperfection are analyzed and the corresponding conclusions are presented.
基金supported by the National Natural Science Foundation of China(No.51477002)the University Synergy Innovation Program of Anhui Province,China(No.GXXT-2019-028).
文摘The development of 3D structural composites with electromagnetic(EM)wave absorption could attenuate EM waves.Herein,magnetized flower-like Cu_(9)S_(5)/ZnFe_(2)O_(4)composites were fabricated through a multistep hydrothermal method.The crystallographic and surface phase chemical information,morphological structure,and magnetic and EM parameters of the composites were analyzed.The prepared Cu_(9)S_(5)/ZnFe_(2)O_(4)composites have multiple loss paths for EM waves and present an overall 3D flower-like structure.The Cu_(9)S_(5)/ZnFe_(2)O_(4)composites exhibit a minimum reflection loss of-54.38 dB and a broad effective absorption bandwidth of 5.92 GHz.Through magnetization,ZnFe_(2)O_(4)particles are self-assembled and grown on the surfaces of Cu_(9)S_(5).Such a modification is conducive to the generation of additional cross-linking contact sites and the effective introduction of a large number of phase interfaces,crystalline defects,special three-dimensional flower-like structures,and magneto-electrical coupling loss effects.Moreover,the synergistic effect of multiple loss strategies effectively improves EM wave absorption by the material.This work can provide a strategy for the use of magnetizationmodified sulfide composite functional materials in EM wave absorption.
文摘The multi-polar structure is a new international relationship structure, which differs greatly from both the bi-polar and uni-polar structures in both structure and nature, mainly emerging from the evolution of two aspects： first, the meaning of ＂polar＂ has undergone a major change; and second, beyond the power structure, the relationship structure between nations is much different from the past and is inflicting an increasingly important impact on core implication of the multi-polar the structure. Decentralization is the structure. In the current reality of international politics, decentralization refers to the dissolution of US hegemony, as different nations and power centers are busy competing and cooperating with one another at different levels in accordance with their own advantages and characteristics. Globally, the multi-polar structure manifests a state in which the current power structure is loosening, while international relationships have become more diversified due to their ongoing development. This is the development of a new relationship structure that is of great significance and what calls for our closest attention.
文摘The world is facing the third important global power shift.The United States,EU, Japan,Russia,China,and the newly emerging power group are becoming the six big forces in the international center stage,while the former three forces and the latter three belong to two groups,waning and waxing respectively.The major shift in the global balance of power is bound to give rise to the transitional multi-polar configuration,which implies a shifting of leadership over the configuration,China and U.S.outweighing other forces,global issues looming large,homogeneity blending with heterogeneity,and a shifting center of world powers.The transitional multi-polar configuration is all about change,upon which China is one of the decisive forces.
基金supported by the National Key R&D Program of China(No.2021YFB2800700)the National Natural Science Foundation of China(No.12274210)Partial support is from NSF of Jiangsu Province(No.BK20243062).
文摘The rapid development of microwave-terahertz frequency band technologies has created an urgent demand for broadband electromagnetic wave absorption materials.In this study,a heterostructured composite comprising mixed-phase 1T/2H-MoSe_(2)(002)and WO_(3)(200)nanosheets was constructed to realize efficient electromagnetic wave absorption and shielding across both microwave and terahertz frequency bands.In the microwave region,the 1T/2H-MoSe_(2)/WO_(3)absorber exhibits a minimum reflection loss of-66.62 dB at 14.98 GHz with a thickness of 1.77 mm,attributed to slow polarization relaxation induced by multiple interfaces and structural defects.In the terahertz range,the system delivers a dominant shielding effectiveness of 67.3 dB at 1.31 THz with a thickness of 2 mm.This performance arises from the precise alignment of the Fermi level of metallic 1T-MoSe_(2)with the conduction band of WO_(3)at the interface,enabling rapid electron injection into WO_(3)with oxygen vacancies via electrochromism.This process induces the transition from W(VI)–O to W(VI-)–O,thereby enhancing both electronic and ionic polarization losses.When incorporated into polyvinyl alcohol(PVA)and fabricated into films,the resulting 500-μm-thick(1T/2H-MoSe_(2))/WO_(3)/PVA composite film achieves a maximum shielding effectiveness of 71.51 dB in the 0.2–1.8 THz frequency range,demonstrating excellent practical applicability.
