Spectral bandpass filters serving as crucial signal processing components are widely applied in various electromagnetic/optical systems.However,the filtering of reflection signal always faces problems of notably accom...Spectral bandpass filters serving as crucial signal processing components are widely applied in various electromagnetic/optical systems.However,the filtering of reflection signal always faces problems of notably accompanied transmission or strict angular limit.Here,we propose novel transmissionless metagratings for specular-reflection bandpass filtering under wide oblique incidence angles.The metagratings are composed of metallic groove gratings and high-refractive-index dielectric particles,which of them respectively provide continuum of localized cavity mode and discrete magnetic dipole resonance under oblique transverse magnetic waves,and produce broadband and narrowband anomalous reflection.Their destructive interference gives rise to a Fano-type narrow bandpass filter in the specular reflection.By integrating CaTiO3ceramic particles with metallic groove gratings,we experimentally demonstrate a single-bandpass metagrating filter at microwave frequency which exhibits a low insertion loss and narrow bandwidth under wide-angle oblique incidence,and agrees with simulations well.Furthermore,by arranging two different sized CaTiO3ceramic particles or changing the temperature,the metagrating filter is endowed with dual-bandpass or thermally tunable feature,respectively.Finally,the design is extended to terahertz frequencies by improving the structure to a double-groove configuration.The proposed composite metagratings with novel bandpass filtering function and angular insensitivity not only enrich the category of spatial filter but have promising applications in microwave communication systems and optical devices.展开更多
We theoretically study the differential conductance of a graphene/graphene superconductor junction, where the valley polarization of Dirac electrons is considered in the nonsuperconducting region. It is shown that the...We theoretically study the differential conductance of a graphene/graphene superconductor junction, where the valley polarization of Dirac electrons is considered in the nonsuperconducting region. It is shown that the subgap conductance will increase monotonically with the valley-polarization strength when the chemical potential μ is near the Dirac point μ≤ 3？（？ is the superconducting gap）, whereas it will decrease monotonically when μ is far away from the Dirac point, μ≥ 5？.The former case is induced by the specular Andreev reflection while the retro-reflection accounts for the later result. Our findings may shed light on the control of conductance of a graphene superconductor junction by valley polarization.展开更多
A sensing system is developed to measure the weld pool boundary and pool suoface deformation in gas tungsten arc welding. LaserStrobe technique is used to eliminate the strong arc light inteoference, and specular refl...A sensing system is developed to measure the weld pool boundary and pool suoface deformation in gas tungsten arc welding. LaserStrobe technique is used to eliminate the strong arc light inteoference, and specular reflection from the pool suoface is sensed to describe the relation between the deformed stripes and pool surface depression. Clear images of both the pool boundary and the deformed stripes edges are obtained during gas tungsten arc welding process, which lays foundation for realtime monitoring the pool suoface depression and weld penetration.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51902175)the Fundamental Research Funds for the Central Universities(Grant No.06500174)the National Postdoctoral Program for Innovative Talents(Grant No.BX20180153)。
文摘Spectral bandpass filters serving as crucial signal processing components are widely applied in various electromagnetic/optical systems.However,the filtering of reflection signal always faces problems of notably accompanied transmission or strict angular limit.Here,we propose novel transmissionless metagratings for specular-reflection bandpass filtering under wide oblique incidence angles.The metagratings are composed of metallic groove gratings and high-refractive-index dielectric particles,which of them respectively provide continuum of localized cavity mode and discrete magnetic dipole resonance under oblique transverse magnetic waves,and produce broadband and narrowband anomalous reflection.Their destructive interference gives rise to a Fano-type narrow bandpass filter in the specular reflection.By integrating CaTiO3ceramic particles with metallic groove gratings,we experimentally demonstrate a single-bandpass metagrating filter at microwave frequency which exhibits a low insertion loss and narrow bandwidth under wide-angle oblique incidence,and agrees with simulations well.Furthermore,by arranging two different sized CaTiO3ceramic particles or changing the temperature,the metagrating filter is endowed with dual-bandpass or thermally tunable feature,respectively.Finally,the design is extended to terahertz frequencies by improving the structure to a double-groove configuration.The proposed composite metagratings with novel bandpass filtering function and angular insensitivity not only enrich the category of spatial filter but have promising applications in microwave communication systems and optical devices.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274059 and 11074233)
文摘We theoretically study the differential conductance of a graphene/graphene superconductor junction, where the valley polarization of Dirac electrons is considered in the nonsuperconducting region. It is shown that the subgap conductance will increase monotonically with the valley-polarization strength when the chemical potential μ is near the Dirac point μ≤ 3？（？ is the superconducting gap）, whereas it will decrease monotonically when μ is far away from the Dirac point, μ≥ 5？.The former case is induced by the specular Andreev reflection while the retro-reflection accounts for the later result. Our findings may shed light on the control of conductance of a graphene superconductor junction by valley polarization.
文摘A sensing system is developed to measure the weld pool boundary and pool suoface deformation in gas tungsten arc welding. LaserStrobe technique is used to eliminate the strong arc light inteoference, and specular reflection from the pool suoface is sensed to describe the relation between the deformed stripes and pool surface depression. Clear images of both the pool boundary and the deformed stripes edges are obtained during gas tungsten arc welding process, which lays foundation for realtime monitoring the pool suoface depression and weld penetration.
