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1.
Electronic imaging of complex cylindrical objects with arbitrary cross sections was investigated, assuming an incident wave upon both penetrable inhomogeneous dielectric cylinders and perfectly conducting cylinders with known shape, and external measurements of the scanned field. By properly processing the scattered held measurements, the dielectric permittivity distribution of the scanned object can be reconstructed. A theoretical formulation was based on proper arrangement of the incident field directions resulting in a set of integral equations derived and solved by the moment method and the unrelated illumination method. Numerical results demonstrate the capability of the imaging algorithm. Good reconstruction results were obtained even in the presence of additive random noise. In addition, noise effects on the reconstruction results were investigated. 相似文献
2.
本文将B样条函数应用于根据多入射方向下的后散射场对二维导体柱横截面形状的反演,并将整个反演过程转化为两次非线性优化过程。由于两次优化的目标函数的导数都是可求得的,因此采用基于梯度的优化算法,如Broyden-Fletcher-Goldfard-Shanno变尺度算法(简称BFGS方法)。第一次优化最佳的等效圆柱的半径和深度,然后在第二次优化过程中再进一步优化导体柱横截面的控制节点以得到反演的形状。最后,以数值结果验证了该方法的有效性,并讨论了该方法的抗噪声性能。 相似文献
3.
The problem of scattering from a corrugated conducting cylinder due to an obliquely incident plane wave is solved by a boundary-value method. The region between the corrugations is considered as a medium with tensor permeability and tensor permittivity, which is a valid assumption when the corrugation constant is much less than the free-space wavelength. By loading this region with a dielectric material, one of the components of the scattered electric field in the far-field region can be altered significantly with no change in the other component. These components, in turn, determine the bistatic scattering cross sections, and the dielectric loading of the corrugated region appears to have no effect on the cross section due to the polarized component, while showing significant changes in the cross section due to the depolarized component 相似文献
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E. A. Shorokhova 《Journal of Communications Technology and Electronics》2007,52(5):493-502
A finite circular magnetodielectric conducting cylinder located in a conducting medium with arbitrary permittivity and permeability is considered. The method of induced currents is applied to analyze scattering of electromagnetic waves by this cylinder in the case when the incident field is excited by elementary sources. The effect of the parameters of the cylinder on the meridional and azimuthal components of the total electric field produced by a radial electric dipole is investigated numerically. 相似文献
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Microwave imaging for a dielectric cylinder 总被引:3,自引:0,他引:3
Huang-Tien Lin Yean-Woei Kiang 《Microwave Theory and Techniques》1994,42(8):1572-1579
The problem of reconstructing both the shape and the relative permittivity of a homogeneous dielectric cylinder from the measurement of scattered field is numerically simulated. The Newton-Kantorovitch algorithm and the moment method are used to solve a set of nonlinear integral equations. Numerical results show that, with multiple incident directions, good reconstruction is obtained. This algorithm can be applied at a single frequency without limitation on the value of dielectric constant. The effect of random noise on imaging reconstruction is also investigated 相似文献
6.
This letter deals with a perfectly conducting infinitely long circular cylinder coated with a radially stratified sheath. Scattering of normally incident plane electromagnetic waves is considered. A certain profile of permittivity in the sheath is taken, leading to particularly simple results. 相似文献
7.
Some properties of the electromagnetic field are determined for an unbounded medium characterized by a permittivity tensor whose elements can be expressed as the sum of two terms, one deterministic and the other random. The deterministic and random parts of the permittivity tensor are considered to be uniaxial anisotropic; thus it is a diagonal tensor where two of the three elments are equal. Starting from the bilocal approximation to Dyson's equation, an effective permittivity tensor and mean dyadic Green's function are obtained for small-scale fluctuations. Some important properties of the ordinary and extraordinary waves are also made known. 相似文献
8.
《Microwave Theory and Techniques》1987,35(11):937-945
The diffraction properties of electromagnetic waves propagating in a planar anisotropic medium with tensor permittivity which is modulated periodically with respect to space and time are analyzed by extending the previous theory for time-invariant anisotropic dielectric gratings. The method applies to any isotropic or anisotropic medium, any polarization of the incident plane wave, and any orientation of the grating vector. The analysis is formulated in a unified matrix form so that calculations can be performed systematically. As numerical examples of the general analysis, the optical diffractions by an acoustic wave in a birefringent crystal and by a cholesteric liquid crystal are treated, where the approximate two-wave analysis is also derived and the accuracy is discussed by comparison with the rigorous analysis. 相似文献
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10.
Chien-Ching Chiu Yean-Woei Kiang 《Microwave Theory and Techniques》1991,39(9):1632-1639
A computational approach to the imaging or inverse scattering of an imperfectly conducting cylinder is presented. A conducting cylinder of unknown shape and conductivity scatters the incident wave in free space and the scattered field is recorded on a circle surrounding the scatterer. By properly processing the scattered data, the shape and conductivity of the scatterer can be reconstructed. The problem is formulated in the form of nonlinear integral equations, which can be solved numerically by the Newton-Kantorovitch algorithm. The pseudoinverse technique is used to overcome the ill-posedness, and the condition number of the matrix is also discussed. Numerical examples are given to illustrate the capability of the inversion algorithm using the simulated scattered fields in both near and far zones. Multiple incident directions permit good reconstruction of shape and, to a lesser extent, conductivity in the presence of noise in measured data 相似文献
11.
B. Z. Katsenelenbaum 《Journal of Communications Technology and Electronics》2014,59(11):1095-1100
A metal body can be made invisible for a radar (radar-protected) through covering it with a dielectric film. The invisibility means that the scattered (diffraction) field induced when a plane wave radiated by a radar is incident on a body has a zero amplitude in the direction toward the radar and that this situation occurs for any direction of the arrival of an arbitrarily polarized incident wave. The permittivity of the film should be anisotropic, complex, and different on different sections of a body’s surface. A system of equations from which this permittivity can be found is derived. The problem of protection of a cylinder of an arbitrary section is considered in detail. 相似文献
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13.
《Microwave Theory and Techniques》1986,34(11):1202-1207
Complex values of the permittivity tensor of robber sheets which are manufactured by the rolling process were estimated by the least-squares method using the reflection coefficient measured for normal incidence. First, the frequency characteristics of the reflection coefficients of a rubber sheet backed by thin aluminum were measured from 8.5 to 10.5 GHz by changing the rolling angle relative to the incident electric field. Next, the elements of the permittivity tensor were determined by the least-squares method from many data of measured reflection coefficients of the samples. Five kinds of rubber sheets containing carbon particles or fibers were selected, and circular pieces 30 cm in diameter were measured by this method. The complex permittivity tensors including off-diagonal elements were thus obtained, and the principal directions of the tensor were calculated from the measured permittivity tensor. The following facts were found through this analysis: The permittivity element in the rolling direction is about five times larger and the off-diagonal elements are small compared with the diagonal elements. The principal direction of the real part is different from that of the imaginary part for a certain kind of rubber sheet mixed with carbon particles. 相似文献
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A finite cylinder with arbitrary conductivity and permittivity is illuminated by an EM wave. The induced current in and the scattered field by the cylinder are determined based on the numerical solution of a tensor integral equation. An experiment has been conducted to verify the theory. Biological and metallic cylinders are emphasized in the study. 相似文献
17.
The performance of the Born iterative method of nonlinear two-dimensional profile inversion is examined for the reconstruction of large objects and in the presence of measurement noise. Time-domain data are used. It is shown that objects at least as large as about nine wavelengths can be inverted without any convergence problems. The algorithm is shown to perform well in the presence of 10% noise, or 20-dB signal-to-noise ratio. The simultaneous inversion of permittivity and conductivity profiles is formulated and solved using the Born iterative method. Objects with various loss tangents are reconstructed, and the limits of applicability of the algorithm are investigated 相似文献
18.
An inverse scattering method to reconstruct simultaneously the permittivity profile and the conductivity profile of one-dimensional inhomogeneons medium which makes use of the transverse electric (TE) wave and/or transverse magnetic (TM) wave, is proposed. The medium is illuminated by the TE and/or TM plane wave at oblique incidence, and the data are taken as the reflection coefficients for a set of discrete frequencies and/or a finite number of incident angles. Furthermore, the reflection coefficient data contain the Gaussian noise. The nonlinear integral equation relating the unknown constitutive parameter of the medium to the reflection coefficient for TE wave and/or TM wave is solved by the Newton iteration method. The inverse operator in the Newton method is determined by the regularization method. It is demonstrated in terms of the numerical examples that this method utilizing both polarizations and the incident angle of the incident plane wave is very effective even if the reflection coefficient contains the practical measurement error, or the phase of the reflection coefficient is unknown. Moreover, the relationships between the errors of reconstructed profile and the measured reflection coefficient are also discussed. 相似文献
19.
The finite-element method for propagation in planar anisotropic diffused optical waveguides with arbitrary permittivity tensor is presented. A Galerkin procedure has been introduced to the finite-element formulation, to study both the nonleaky and leaky surface waves. The complex propagation constants are determined as a function of frequency for possible modes of propagation. The accuracy of the method has been checked by calculating the nonleaky and leaky surface waves of Ti-diffused LiNbO3 waveguides with Gaussian index profiles. The numerical results of Ti-diffused LiNbO3 waveguides with dielectric overlays are also presented and the effects of dielectric overlays on the propagation characteristics for the nonleaky and leaky surface waves are examined. 相似文献
20.
《AEUE-International Journal of Electronics and Communications》2014,68(9):877-882
An effective non-iterative method is developed for determination electromagnetic parameters of complex materials with anisotropy. Unlike the existing methods, the proposed method can extract the electromagnetic tensor parameters of materials with off-diagonal anisotropy using co- and cross-polarized reflection and transmission without using iterative procedures. Useful analytical expressions are derived for extracting the medium parameters of materials with off-diagonal anisotropy. The advantage of the method is that it uses state transition matrix and its properties in order to avoid nonlinearity and complexity of the problem. The method can work very well for dispersive materials since it is based on frequency-by-frequency extraction. The proposed method is validated by extraction of the complex permittivity and permeability tensors of two typical anisotropic materials. 相似文献