共查询到20条相似文献,搜索用时 15 毫秒
1.
A rigorous spectral solution for three-dimensional (3D) electromagnetic scattering by the edge of an anisotropic impedance half-plane with a perfect electric conducting (PEC) face is presented. The surface impedance tensor of the loaded face is characterised by: (i) principal anisotropy axes arbitrarily oriented with respect to the diffracting edge; (ii) a vanishing surface impedance along a principal anisotropy axis and an arbitrary impedance in the orthogonal direction 相似文献
2.
Manara G. Nepa P. Pelosi G. Vallecchi A. 《Antennas and Propagation, IEEE Transactions on》2004,52(2):487-496
High-frequency expressions for the field scattered by a half-plane with a perfectly conducting and an anisotropic impedance face are provided in the format of the uniform geometrical theory of diffraction (UTD), when the half-plane is illuminated by an arbitrarily polarized plane wave obliquely incident on its edge. The loaded face is characterized by a tensor surface impedance with principal anisotropy axes arbitrarily oriented with respect to the edge; a vanishing surface impedance is exhibited in one of the principal directions. This kind of tensor surface impedance can be suitably applied for analyzing the effects on the scattered field of corrugated surfaces or grounded dielectric slabs periodically loaded by metallic strips. This solution extends previous high-frequency formulations valid in those cases in which the direction of corrugations or strips is either parallel or perpendicular to the edge. The analysis is performed by resorting to the Sommerfeld-Maliuzhinets method. To determine the spectral solution, a special function is needed that differs from the standard Maliuzhinets one and was originally introduced to study the electromagnetic scattering by a wedge embedded in a gyroelectric medium. 相似文献
3.
The diffraction of an arbitrarily polarized electromagnetic plane wave obliquely incident on the edge of a right-angled anisotropic impedance wedge with a perfectly conducting face is analyzed. The impedance tensor on the loaded face has its principal anisotropy axes along directions parallel and perpendicular to the edge, exhibiting arbitrary surface impedance values in these directions. The proposed solution procedure applies both to the exterior and the interior right-angled wedges. The rigorous spectral solution for the field components parallel to the edge is determined through the application of the Sommerfeld-Maliuzhinets technique. A uniform asymptotic solution is provided in the framework of the uniform geometrical theory of diffraction (UTD). The diffracted field is expressed in a simple closed form involving ratios of trigonometric functions and the UTD transition function. Samples of numerical results are presented to demonstrate the effectiveness of the asymptotic expressions proposed and to show that they contain as limit cases all previous three-dimensional (3-D) solutions for the right-angled impedance wedge with a perfectly conducting face 相似文献
4.
The three-dimensional electromagnetic (EM) scattering from half and full plane configurations, both characterized by a perfectly conducting and an anisotropic impedance face, is analyzed. The anisotropic impedance boundary condition considered for the loaded face is suitable for modeling corrugated surfaces or strip-loaded grounded dielectric slabs used to realize artificially hard or soft surfaces, with a tensor surface impedance exhibiting a vanishing impedance along the corrugations or strips and a diverging impedance in the orthogonal direction. Previous rigorous solutions, valid when the vanishing impedance direction is either parallel or perpendicular to the edge, are generalized here to the case in which the direction of vanishing impedance is arbitrarily oriented 相似文献
5.
The surface impedance concept is used to examine the effect of ground anisotropy on the radiated field and power dissipation of a horizontal ELF transmitting array. The principal result, for a simple homogeneous but anisotropic ground, is that even though the ground skews the antenna pattern, any attempt to reorient the array to steer the pattern peak towards the receiver incurs an increase in power dissipation. In fact, the power dissipation is minimized by steering the pattern peak even further away from the receiver. 相似文献
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Influence of anisotropic conductivity on EEG source reconstruction: investigations in a rabbit model
Güllmar D Haueisen J Eiselt M Giessler F Flemming L Anwander A Knösche TR Wolters CH Dümpelmann M Tuch DS Reichenbach JR 《IEEE transactions on bio-medical engineering》2006,53(9):1841-1850
The aim of our work was to quantify the influence of white matter anisotropic conductivity information on electroencephalography (EEG) source reconstruction. We performed this quantification in a rabbit head using both simulations and source localization based on invasive measurements. In vivo anisotropic (tensorial) conductivity information was obtained from magnetic resonance diffusion tensor imaging and included into a high-resolution finite-element model. When neglecting anisotropy in the simulations, we found a shift in source location of up to 1.3 mm with a mean value of 0.3 mm. The averaged orientational deviation was 10 degree and the mean magnitude error of the dipole was 29%. Source localization of the first cortical components after median and tibial nerve stimulation resulted in anatomically verified dipole positions with no significant anisotropy effect. Our results indicate that the expected average source localization error due to anisotropic white matter conductivity is within the principal accuracy limits of current inverse procedures. However, larger localization errors might occur in certain cases. In contrast, dipole orientation and dipole strength are influenced significantly by the anisotropy. We conclude that the inclusion of tissue anisotropy information improves source estimation procedures. 相似文献
8.
E. N. Korshunova V. P. Mal’tsev A. D. Shatrov 《Journal of Communications Technology and Electronics》2011,56(3):289-293
The properties of circularly polarized surface waves propagating along a plane boundary with an anisotropic chiral impedance
are investigated. Boundaries with rectangular and radial-ring structures of anisotropy are considered. The problem of the
normal incidence of plane circularly polarized waves on such boundaries is solved. 相似文献
9.
The ionospheric anisotropy is considered with horizontal magnetic field either for transverse (East-West or West-East) or for longitudinal (South-North) propagation. For transverse propagation in a vertically stratified medium the differential equations of the various field components are uncoupled and a closed form solution is given for identical exponential height variation of the components of tensor conductivity. For arbitrary height variation of the tensor conductivity numerical solutions are obtained after expressing the surface impedance below the ionosphere in terms of a Riccati-type differential equation. The West-East direction of propagation exhibits a lower attenuation constant than the East-West direction forf < 1000 cps. This is contrary to the expectations based on a model of a homogeneous anisotropic ionosphere. For longitudinal propagation the differential equations of the various field components are coupled, with the coupling being particularly strong above theD region. The differential equations are simplified by assuming no coupling in the lower ionosphere and strong coupling above a pre-selected altitudey_{1} . For exponential height variation of the tensor conductivity components the closed form solution differs negligibly from the isotropic case. For arbitrary height varition of the tensor conductivity numerical solutions are obtained similarly as for the transverse propagation. Over most of the frequency range the attenuation figures for South-North propagation are intermediate between the corresponding figures for West-East and East-West propagation. 相似文献
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Dynamic Analysis of Microstrip Lines and Finlines on Uniaxial Anisotropic Substrates 总被引:1,自引:0,他引:1
《Microwave Theory and Techniques》1987,35(10):881-886
Dyadic Green's functions in the Fourier transform spectral domain are obtained for open microstrip lines and bilateral finlines on uniaxial anisotropic substrates. These functions are written in an impedance matrix form by expressing the electric and magnetic fields in terms of Hertz vector potentials oriented along the optical axis. In combination with Galerkin's method, they are used to obtain the propagation characteristics of single and parallel coupled microstrip lines on uniaxial anisotropic substrates having the optical axis in an arbitrary direction in a transverse plane and of bilateral finlines with the three optical axis orientations of the uniaxial anisotropic substrate that result in the diagonal permittivity tensor. 相似文献
12.
《IEEE transactions on medical imaging》2009,28(12):1914-1928
13.
In this paper, a full-wave spectral-domain integral-equation technique is used to study double substrate layer coplanar devices with the ferroelectric thin film adjacent to the conductor guiding interfacial surface. The Green's function is used in the anisotropic situation for anisotropic permittivities. In examining specific laboratory data, going from an unbiased static electric field to the biased case, the permittivity tensor is allowed to go from a unity tensor to a uniaxial one. Consistent with this permittivity tensor behavior, the attenuation trend with frequency and its amplitude is also found 相似文献
14.
Mikhail A. Ljalinov 《电信纪事》1994,49(11-12):667-672
When boundary conditions on a surface of a wedge are anisotropic impedance ones, the problem of diffraction is reduced to a coupled system of Maliuzhinets’ equations via Sommerfeld integral. For weak anisotropy a regular asymptotic method is developed to compute the leading terms and the first correction of spectral functions. Electromagnetic field which arises due to anisotropy is presented in closed form. Analytic properties of spectral functions are investigated. Uniform asymptotics for the scattered field are constructed via matching of local asymptotic expansions. 相似文献
15.
Hunsberger F. Luebbers R. Kunz K. 《Antennas and Propagation, IEEE Transactions on》1992,40(12):1489-1495
When subjected to a constant magnetic field, both plasmas and ferrites exhibit anisotropic constitutive parameters. For electronic plasmas this anisotropy must be described by using a permittivity tensor in place of the usual scalar permittivity. Each member of this tensor is also very frequency dependent. A finite-difference time-domain formulation which incorporates both anisotropy and frequency dispersion, enabling the wideband transient analysis of magnetoactive plasma, is described. Results are shown for the reflection and transmission through a magnetized plasma layer, with the direction of propagation parallel to the direction of the biasing field. A comparison to frequency-domain analytic results is included 相似文献
16.
提出了一种张量人工阻抗单元的表面阻抗分析计算方法,主要对矩形形状单元的表面阻抗开展了研究。通过仿真软件Ansys-HFSS提取了人工阻抗单元表面的入射散射场,再利用等效传输线技术计算出表面的张量阻抗。利用张量阻抗与表面场的关系,给出了人工阻抗单元的标量阻抗与传播方向的关系,验证了计算的准确性。最后作为实例,设计了一种基于张量阻抗单元的圆极化全息天线,天线具有较好的圆极化特性,增益大于21 dB。 相似文献
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Radiation and scattering from a microstrip patch on a uniaxial substrate 总被引:13,自引:0,他引:13
The problem of a rectangular microstrip antenna printed on a uniaxially anisotropic substrate is treated. The effect of anisotropy on the resonant frequency and surface wave excitation of the antenna is considered, and the radar cross section (RCS) of the antenna is calculated. The RCS calculation includes the effect of the load impedance (antenna mode scattering). Results for the resonant frequency of a patch on a uniaxial substrate are compared with measurements, and the RCS of a patch on an isotropic substrate is compared with measurements. The derivation of the uniaxial Green's function in spectral form, the associated moment method analysis for the input impedance and scattering of the microstrip patch, and the expressions for the far-zone fields of a source on a uniaxial substrate are presented. 相似文献
19.
《Microwave Theory and Techniques》1985,33(5):419-421
The characteristic impedance of the slab line with a circular conductor having an anisotropic dielectric is presented by rising the affine and conformal transformations. Moreover, a simpler approximate formula of the impedance expressed in term of epsilon /spl par/, epsilon /spl perp/, and r/h is also presented, where epsilon /spl par/, epsilon /spl perp/ r, and h, are the principal axes-relative dielectric constants of the anisotropic dielectric, the inner conductor radius, and the half Iength between ground planes, respectively. 相似文献
20.
The neurosurgical method of deep brain stimulation (DBS) is used to treat symptoms of movement disorders like Parkinson's disease by implanting stimulation electrodes in deep brain areas. The aim of this study was to examine the field distribution in DBS and the role of heterogeneous and anisotropic material properties in the brain areas where stimulation is applied. Finite element models of the human brain were developed comprising tissue heterogeneity and anisotropy. The tissue data were derived from averaged magnetic resonance imaging and diffusion tensor imaging datasets. Unilateral stimulation of the subthalamic nucleus (STN) was computed using an accurate model of an electrode used in clinical treatment of DBS extended with an encapsulation layer around the electrode body. Computations of anisotropic and isotropic brain models, which consider resistive tissue properties for unipolar and bipolar electrode configurations, were carried out. Electrode position was varied within an area around the stimulation center. Results have shown a deviation of 2% between anisotropic and isotropic field distributions in the vicinity of the STN. The sensitivity of this deviation referring to the electrode position remained small, but increased when the electrode position approached areas of high anisotropy. 相似文献