In this paper, a low-profile wideband dielectric resonator antenna(DRA) with a very compact planar size is investigated. The antenna consists of a high permittivity dielectric sheet on the top, a low permittivity subs...In this paper, a low-profile wideband dielectric resonator antenna(DRA) with a very compact planar size is investigated. The antenna consists of a high permittivity dielectric sheet on the top, a low permittivity substrate in the middle, and a probe feeding structure at the bottom. By digging an annular slot in the designated area of the square dielectric sheet, the resonant frequency of fundamental TE111 mode can be effectively increased to be close to the high-order TE131 mode. The two modes can be finally merged together, yielding a wide impedance bandwidth of16.6%. Most importantly, the combination of the two modes is done on the premise of a fixed antenna planar size, which can be very compact and suitable for beam-scanning applications. A probe feeding structure is used to excite the DRA, making the antenna simple and practical to be integrated with other RF circuits. For verification, antenna prototypes with singlefeed linear polarization and differential-feed dual polarization were fabricated and measured. Reasonable agreement between the measured and simulated results is observed.展开更多
Due to the exponentially growing global mobile data of wireless communications evolving from 5 G to 6 G in recent years,research activities of leveraging terahertz(THz)waves to obtain larger channel capacities have sh...Due to the exponentially growing global mobile data of wireless communications evolving from 5 G to 6 G in recent years,research activities of leveraging terahertz(THz)waves to obtain larger channel capacities have shown an ever-increasing pace and reached an unprecedented height than before.Historically,the past few decades have already witnessed much progress in THz generation and detection technologies,which have been recognized for a long time as the bottleneck preventing the THz waves from being tamed by human beings.How-ever,the importance of developing advanced components such as antennas,transmission lines,filters,power amplimers,etc.,which constitute the basic building blocks of a THz wireless system,should not be overlooked for the sake of exploiting the THz spectra for future advanced wireless communications,sensing and imaging applications.While producing a scannable highly-directive antenna beam proves to be indispensable in the pe-riod of microwaves,the significance of such functionality is more critical in the THz era,considering that THz waves have more intractable challenges such as the severity of free-space propagation losses,the susceptibility to atmospheric environments,and the unavailability of efficient signal sources.This article is structured under this background,which is dedicated to reviewing several enabling beam-scanning antenna concepts,structures,and architectures that have been developed for THz wireless systems.Specifically,we divide these THz beam-scanning solutions into four basic groups based on different mechanisms,i.e.,mechanical motion,phased array,frequency beam-scanning,and reconfigurable metasurfaces.展开更多
The sealing performance of a bentonite barrier is highly dependent on its seepage characteristics, which are directly related to the characteristics of its pore structure. Based on scanning electron microscopy(SEM) an...The sealing performance of a bentonite barrier is highly dependent on its seepage characteristics, which are directly related to the characteristics of its pore structure. Based on scanning electron microscopy(SEM) and focused ion beam-SEM(FIB-SEM), the pore structure of bentonite was characterized at different scales. First, a reasonable gray threshold was determined through back analysis, and the image was binarized based on the threshold. In addition, binary images were used to analyze bentonite’s pore structure(porosity and pore size distribution). Furthermore, the effects of different algorithms on the pore structure characterization were evaluated. Then, permeability calculations were performed based on the previous pore structure characteristics and a modified permeability prediction model. For permeability prediction based on the three-dimensional model, the effect of pore tortuosity was also considered. Finally, the accuracy of numerical calculations was verified by conducting macroscopic gas and alcohol permeability experiments. This approach provides a better understanding of the microscale mechanism of gas transport in bentonite and the importance of pore structures at different scales in determining its seepage characteristics.展开更多
For present solid oxide fuel cells(SOFCs),rapid performance degradation is observed in the initial aging process,and the dis-cussion of the degradation mechanism necessitates quantitative analysis.Herein,focused ion b...For present solid oxide fuel cells(SOFCs),rapid performance degradation is observed in the initial aging process,and the dis-cussion of the degradation mechanism necessitates quantitative analysis.Herein,focused ion beam-scanning electron microscopy was em-ployed to characterize and reconstruct the ceramic microstructures of SOFC anodes.The lattice Boltzmann method(LBM)simulation of multiphysical and electrochemical processes in the reconstructed models was performed.Two samples collected from industrial-size cells were characterized,including a reduced reference cell and a cell with an initial aging process.Statistical parameters of the reconstructed microstructures revealed a significant decrease in the active triple-phase boundary and Ni connectivity in the aged cell compared with the reference cell.The LBM simulation revealed that activity degradation is dominant compared with microstructural degradation during the initial aging process,and the electrochemical reactions spread to the support layer in the aged cell.The microstructural and activity de-gradations are attributed to Ni migration and coarsening.展开更多
Since leaky-wave antennas(LWAs)have the advantages of high directivity,low loss and structural simplicity,LWAs are very suitable for designing millimeter-wave(mmW)antennas.The purpose of this paper is to review the la...Since leaky-wave antennas(LWAs)have the advantages of high directivity,low loss and structural simplicity,LWAs are very suitable for designing millimeter-wave(mmW)antennas.The purpose of this paper is to review the latest research progress of LWAs for 5G/B5G mobile communication systems.Firstly,the conventional classification and design methods of LWAs are introduced and the effects of the phase constant and attenuation constant on the radiation characteristics are discussed.Then two types of new LWAs for 5G/B5G mobile communication systems including broadband fixed-beam LWAs and frequencyfixed beam-scanning LWAs are summarized.Finally,the challenges and future research directions of LWAs for 5G/B5G mobile communication systems are presented.展开更多
基金supported by the National Natural Science Foundation of China under Grant 62071256National Natural Science Foundation of Jiangsu under Grant BK20201438+1 种基金supported by State Key Laboratory of Millimeter Waves (Nanjing) and Nantong Research Institute for Advanced Communication Technologies (Nantong)sponsored by Qing Lan Project of Jiangsu Province。
文摘In this paper, a low-profile wideband dielectric resonator antenna(DRA) with a very compact planar size is investigated. The antenna consists of a high permittivity dielectric sheet on the top, a low permittivity substrate in the middle, and a probe feeding structure at the bottom. By digging an annular slot in the designated area of the square dielectric sheet, the resonant frequency of fundamental TE111 mode can be effectively increased to be close to the high-order TE131 mode. The two modes can be finally merged together, yielding a wide impedance bandwidth of16.6%. Most importantly, the combination of the two modes is done on the premise of a fixed antenna planar size, which can be very compact and suitable for beam-scanning applications. A probe feeding structure is used to excite the DRA, making the antenna simple and practical to be integrated with other RF circuits. For verification, antenna prototypes with singlefeed linear polarization and differential-feed dual polarization were fabricated and measured. Reasonable agreement between the measured and simulated results is observed.
基金supported by grants from the Natural Science Foundation of Jiangsu Province(BK20241276)the University Grants Committee/Research Grants Council of the Hong Kong Special Administrative Region,China(AoE/E-101/23-N and CityU 9610655)+3 种基金the Start-up Research Fund of Southeast University(RF1028623258)the Key Laboratory for Information Science of Electromagnetic Waves,Fudan University(EMW202401)the National Key Research and Development Program of China(2023YFB2906103)the National Natural Science Foundation of China(62122019).
文摘Due to the exponentially growing global mobile data of wireless communications evolving from 5 G to 6 G in recent years,research activities of leveraging terahertz(THz)waves to obtain larger channel capacities have shown an ever-increasing pace and reached an unprecedented height than before.Historically,the past few decades have already witnessed much progress in THz generation and detection technologies,which have been recognized for a long time as the bottleneck preventing the THz waves from being tamed by human beings.How-ever,the importance of developing advanced components such as antennas,transmission lines,filters,power amplimers,etc.,which constitute the basic building blocks of a THz wireless system,should not be overlooked for the sake of exploiting the THz spectra for future advanced wireless communications,sensing and imaging applications.While producing a scannable highly-directive antenna beam proves to be indispensable in the pe-riod of microwaves,the significance of such functionality is more critical in the THz era,considering that THz waves have more intractable challenges such as the severity of free-space propagation losses,the susceptibility to atmospheric environments,and the unavailability of efficient signal sources.This article is structured under this background,which is dedicated to reviewing several enabling beam-scanning antenna concepts,structures,and architectures that have been developed for THz wireless systems.Specifically,we divide these THz beam-scanning solutions into four basic groups based on different mechanisms,i.e.,mechanical motion,phased array,frequency beam-scanning,and reconfigurable metasurfaces.
基金support of the National Natural Science Foundation of China (Grant Nos. 52174133 and 51809263)China Atomic Energy Authority。
文摘The sealing performance of a bentonite barrier is highly dependent on its seepage characteristics, which are directly related to the characteristics of its pore structure. Based on scanning electron microscopy(SEM) and focused ion beam-SEM(FIB-SEM), the pore structure of bentonite was characterized at different scales. First, a reasonable gray threshold was determined through back analysis, and the image was binarized based on the threshold. In addition, binary images were used to analyze bentonite’s pore structure(porosity and pore size distribution). Furthermore, the effects of different algorithms on the pore structure characterization were evaluated. Then, permeability calculations were performed based on the previous pore structure characteristics and a modified permeability prediction model. For permeability prediction based on the three-dimensional model, the effect of pore tortuosity was also considered. Finally, the accuracy of numerical calculations was verified by conducting macroscopic gas and alcohol permeability experiments. This approach provides a better understanding of the microscale mechanism of gas transport in bentonite and the importance of pore structures at different scales in determining its seepage characteristics.
基金the National Key R&D Program of China(No.2018YFB1502201)the Guangdong Basic and Applied Basic Research Foundation,China(No.2020A1515010551).
文摘For present solid oxide fuel cells(SOFCs),rapid performance degradation is observed in the initial aging process,and the dis-cussion of the degradation mechanism necessitates quantitative analysis.Herein,focused ion beam-scanning electron microscopy was em-ployed to characterize and reconstruct the ceramic microstructures of SOFC anodes.The lattice Boltzmann method(LBM)simulation of multiphysical and electrochemical processes in the reconstructed models was performed.Two samples collected from industrial-size cells were characterized,including a reduced reference cell and a cell with an initial aging process.Statistical parameters of the reconstructed microstructures revealed a significant decrease in the active triple-phase boundary and Ni connectivity in the aged cell compared with the reference cell.The LBM simulation revealed that activity degradation is dominant compared with microstructural degradation during the initial aging process,and the electrochemical reactions spread to the support layer in the aged cell.The microstructural and activity de-gradations are attributed to Ni migration and coarsening.
基金the National Natural Science Foundation of China(NSFC)under Grants 62071306 and 61801299in part by the Mobil⁃ity Program for Taiwan Young Scientists under Grant RW2019TW001and in part by Shenzhen Science and Technology Program under Grants GJHZ20180418190529516 and JSGG20180507183215520.
文摘Since leaky-wave antennas(LWAs)have the advantages of high directivity,low loss and structural simplicity,LWAs are very suitable for designing millimeter-wave(mmW)antennas.The purpose of this paper is to review the latest research progress of LWAs for 5G/B5G mobile communication systems.Firstly,the conventional classification and design methods of LWAs are introduced and the effects of the phase constant and attenuation constant on the radiation characteristics are discussed.Then two types of new LWAs for 5G/B5G mobile communication systems including broadband fixed-beam LWAs and frequencyfixed beam-scanning LWAs are summarized.Finally,the challenges and future research directions of LWAs for 5G/B5G mobile communication systems are presented.
