The paper is concerned with the reconstruction of a defect in the core of a two-dimensional open waveguide from the scattering data. Since only a finite numbers of modes can propagate without attenuation inside the co...The paper is concerned with the reconstruction of a defect in the core of a two-dimensional open waveguide from the scattering data. Since only a finite numbers of modes can propagate without attenuation inside the core, the problem is similar to the one-dimensional inverse medium problem. In particular, the inverse problem suffers from a lack of uniqueness and is known to be severely ill-posed. To overcome these difficulties, we consider multi-frequency scattering data. The uniqueness of solution to the inverse problem is established from the far field scattering information over an interval of low frequencies.展开更多
Millimeter-wave traveling-wave tube （TWT） prevails nowadays as the amplifier for radar, communication and electronic countermeasures. The rectangular waveguide grating is a promising all-metal interaction circuit fo...Millimeter-wave traveling-wave tube （TWT） prevails nowadays as the amplifier for radar, communication and electronic countermeasures. The rectangular waveguide grating is a promising all-metal interaction circuit for the millimeter-wave TWT with advantages of high power capacity, fine heat dissipation, scalability to smaller dimen- sions for shorter wavelengths, compact structure and robust performance. Compared with the traditional closed structure, the open rectangular waveguide grating （ORWG） has wider bandwidth, lower cut-off frequency, and higher machining precision for higher working frequencies due to the open transverse. It is a potential structure that can work in the millimeter wave and even Terahertz band. The rf characteristics including dispersion and interaction impedance are investigated by both theoretic calculation and software simulation. The influences of the structure parameters are also discussed and compared, and the theoretical results agree well with the simula- tion results. Based on the study, the ORWG will favor the design of a broadband and high-power millimeter-wave TWT.展开更多
The paper discusses the effect of the waveguidc walls on magnetic polarizability tensor of the end opening. The solution is given on the basis of application of a new Greed's function which is constructed by takin...The paper discusses the effect of the waveguidc walls on magnetic polarizability tensor of the end opening. The solution is given on the basis of application of a new Greed's function which is constructed by taking into account the mirror image retlection of the waveguide walls.展开更多
We extend classic Sommerfeld and Silver-Muller radiation conditions for bounded scatterers to acoustic and electromagnetic fields propagating over three isotropic homogeneous layers in three dimensions.If x=(x1,x2,x3)...We extend classic Sommerfeld and Silver-Muller radiation conditions for bounded scatterers to acoustic and electromagnetic fields propagating over three isotropic homogeneous layers in three dimensions.If x=(x1,x2,x3)∈R^(3),with x_(3)denoting the direction orthogonal to the layers,standard conditions only hold for the outer layers in the region|x_(3)|>||x||^(γ),forγ∈(1/4,1/2)and x large.For|x_(3)|<||x||^(γ)and inside the slab,asymptotic behavior depends on the presence of surface or guided modes given by the discrete spectrum of the associated operator.展开更多
基金supported by National Science Foundation of USA(Grant Nos.DMS0908325DMS-0968360 and DMS-1211292)+2 种基金Ofce of Naval Research of USA(ONR)(Grant No.N00014-12-10319)National Natural Science Foundation of China(Grant No.91130004)the grant UJF-MSTIC-Plasmons
文摘The paper is concerned with the reconstruction of a defect in the core of a two-dimensional open waveguide from the scattering data. Since only a finite numbers of modes can propagate without attenuation inside the core, the problem is similar to the one-dimensional inverse medium problem. In particular, the inverse problem suffers from a lack of uniqueness and is known to be severely ill-posed. To overcome these difficulties, we consider multi-frequency scattering data. The uniqueness of solution to the inverse problem is established from the far field scattering information over an interval of low frequencies.
基金Supported by the National Natural Science Foundation of China under Grant No 61271029the National Science Fund for Distinguished Young Scholars of China under Grant No 61125103the National Research Foundation of Korea under Grant No MSIP:NRF-2009-0083512
文摘Millimeter-wave traveling-wave tube （TWT） prevails nowadays as the amplifier for radar, communication and electronic countermeasures. The rectangular waveguide grating is a promising all-metal interaction circuit for the millimeter-wave TWT with advantages of high power capacity, fine heat dissipation, scalability to smaller dimen- sions for shorter wavelengths, compact structure and robust performance. Compared with the traditional closed structure, the open rectangular waveguide grating （ORWG） has wider bandwidth, lower cut-off frequency, and higher machining precision for higher working frequencies due to the open transverse. It is a potential structure that can work in the millimeter wave and even Terahertz band. The rf characteristics including dispersion and interaction impedance are investigated by both theoretic calculation and software simulation. The influences of the structure parameters are also discussed and compared, and the theoretical results agree well with the simula- tion results. Based on the study, the ORWG will favor the design of a broadband and high-power millimeter-wave TWT.
文摘The paper discusses the effect of the waveguidc walls on magnetic polarizability tensor of the end opening. The solution is given on the basis of application of a new Greed's function which is constructed by taking into account the mirror image retlection of the waveguide walls.
文摘We extend classic Sommerfeld and Silver-Muller radiation conditions for bounded scatterers to acoustic and electromagnetic fields propagating over three isotropic homogeneous layers in three dimensions.If x=(x1,x2,x3)∈R^(3),with x_(3)denoting the direction orthogonal to the layers,standard conditions only hold for the outer layers in the region|x_(3)|>||x||^(γ),forγ∈(1/4,1/2)and x large.For|x_(3)|<||x||^(γ)and inside the slab,asymptotic behavior depends on the presence of surface or guided modes given by the discrete spectrum of the associated operator.
