On wave modulation by a rotating object

When a time harmonic electromagnetic wave is incident upon a rotating object which is not rotationally symmetric about the axis of rotation, modulation in the secondary waves generally will occur. Two scattering and reflection problems where, under certain conditions, no modulation occurs, are discussed. In the first case, a transverse electric (TE) or transverse magnetic (TM) wave is incident upon an object inside a circular waveguide. The object is rotating about the axis of the waveguide and has periodic characterisitcs in the azimuthal direction with period2pi/N(N: an integer). In the second case, the waveguide is removed, and a linearly polarized plane wave is incident upon the object along its axis of rotation.     

1维光子晶体中TM波的传输公式及其辨析

为了得到1维光子晶体中TM波的传输公式,采用传输矩阵的方法和电磁波的边界条件,推导出TM波在介质层中的特征矩阵及其反射系数和透射系数公式。结果表明,用TE波反射系数和透射系数公式做代换的方法不能得到正确的TM波的反射系数和透射系数公式;对推导出TM波的反射系数和透射系数公式进行了分析,由TM波的反射系数和透射系数公式得出的光强透射率和反射率满足能量守恒;并且推出的TM波反射系数公式不仅能够反映反射波与入射波的数量关系,且能够反映反射波与入射波的位相关系。这些结果对研究1维光子晶体中TM波的传输性质是有帮助的。     

Modeling of cylindrical objects by circular dielectric andconducting cylinders

The scattering of an incident plane wave from an array of parallel circular dielectric and/or conducting cylinders is derived rigorously using a boundary value approach. Both transverse electric (TE) and transverse magnetic (TM) polarized incident plane waves are considered. The validity and accuracy of the method are verified by comparing the numerical results with those based on other available methods. The advantage of the proposed analysis is the simplicity and efficiency in computation. The modeling of two-dimensional objects of arbitrary cross section and composite material is outlined and sample numerical results are presented to illustrate the versatility of the method     

Electromagnetic reflection and tramsission for a dielectric-Ω interface and an Ω slab

A time-harmonic electromagnetic plane wave obliquely incident on a half-space or a slab consisting of a so-called Ω medium is considered. The up- and down-going eigenmodes in the Ω medium are derived and used to calculate the reflection and transmission coefficients for TE and TM modes. The Brewster angles for an Ω half-space are computed. Numerical results for the co- and cross-polarized reflection and transmission coefficients for an Ω slab are presented.     

Three-dimensional scattering by an infinite homogeneous anisotropic circular cylinder: A spectral approach

A set of two coupled integral equations based on a plane wave representation Of the fields in a simply connected and anisotropic medium has been derived in order to handle the problem of scattering by a homogeneous anisotropic cylinder for an obliquely incident plane wave of arbitrary linear polarization. The unknowns are scalar, the range of integration is finite, and the kernels are not singular. Numerical results are presented and discussed in detail. The gyrotropic type case is emphasized, and it is found that as in the isotropic case, the depolarization is the same for transverse electric (TE) and transverse magnetic (TM) incident waves.     

无限周期光子晶体全反射隧穿效应的色散研究

利用色散法研究了TE波和TM波在大于全反射角入射一维无限周期光子晶体的全反射隧穿特性.结果发现了一维无限周期光子晶体中的全反射隧穿效应.得出了TE波和TM波的全反射隧穿导带随入射角的变化规律,TE波和TM波的全反射隧穿导带随周期光学厚度的变化规律.     

基于平面波斜入射的人体信道远场路径损耗建模

人体信道路径损耗计算对植入式通信链路预估具有重要意义.文章利用有耗媒质的电磁场边界条件、反射和透射定理并引入切向等效波阻抗定义,推导出平面波向人体斜入射时各人体组织分界面上的入射角、透射角、反射系数、透射系数、切向等效波阻抗以及各人体组织中的电磁合成波,提出了一种基于平面波向多层有耗媒质斜入射的人体信道远场路径损耗解析模型.然后以植入在肌肉为例,计算了TM波和TE波在5个常用工业通信频率以不同角度斜入射的人体信道电磁场分布与路径损耗,结果显示,电磁波在入射面的反射是影响人体信道路径损耗的关键因素,当频率在1.4 GHz附近时总路径损耗最小,TM波性能优于TE波,且当入射角小于等于30°时,总路径损耗基本保持不变.最后采用COMSOL Multiphysics建立了有限元仿真模型验证解析模型,二者结果高度吻合,最大误差仅为0.039,有力证明了解析模型的正确性和有效性.     

无限周期正负折射率光子晶体的全反射隧穿效应

为了研究一维无限周期正负折射率交替结构光子晶体中光的全反射隧穿效应,利用色散法计算了TE波和TM波在大于全反射角入射一维无限周期正负折射率交替结构光子晶体的色散函数。得出了一维无限周期正负折射率交替结构光子晶体中TE波和TM波的全反射隧穿导带的频率随入射角的变化特性、全反射隧穿导带的频率随负折射材料厚度的变化特性。     

Spectral FDTD: a novel technique for the analysis of oblique incident plane wave on periodic structures

This paper introduces a new technique which calculates the reflection coefficient for the plane wave incident on planar periodic structures. The method referred to as spectral finite-difference time-domain (SFDTD) replaces the conventional single-angle incident wave, with a constant transverse wavenumber (CTW) wave. Because the transverse wavenumbers are constant, the fields have no delay in the transverse plane (x-y plane), and PBC (periodic boundary condition) can be directly implemented in the time domain for both oblique and normal incident waves. The stability criterion for this new FDTD technique is angle-independent and therefore this method works well for incident angles close to grazing (/spl theta/=90/spl deg/) as well as normal incident (/spl theta/=0/spl deg/). This shows the efficiency of the method compared to other available FDTD techniques for the same purpose that force a more restricted stability criterion as angles turns to grazing. The validity of this method is verified by comparing the reflection coefficient calculated by this method with the analytical results of a grounded slab. The results of this technique are also compared with method of moments for a periodic array of metallic patches and a good agreement is observed. A periodic array of metallic patches above a PEC plate is analyzed and the reflection coefficient is calculated over a wide frequency band for angles varying from 0/spl deg/ to close to 90/spl deg/.     

A spectral domain method for remotely probing stratified media

The problem of remotely probing a stratified, lossless, dielectric medium is formulated using the spectral domain method of probing. The response of the medium to a spectrum of plane waves incident at various angles is used to invert the unknown profile. For TE polarization, the electric field satisfies a Helmholtz equation. The inverse problem is solved by means of a new representation for the wave function. The principal step in this inversion is solving a second kind Fredholm equation which is very amenable to numerical computations. Several examples are presented including some which indicate that the method can be used with experimentally obtained data. When the fields exhibit a surface wave behavior, a unique inversion can be obtained only if information about the magnetic field is also available. In this case, the inversion is accomplished by a two-step procedure which employs a formula of Jost and Kohn. Some examples are presented, and an approach which greatly shortens the computations without greatly deteriorating the results is discussed.     

FDTD simulation of TE and TM plane waves at nonzero incidence in arbitrary Layered media

Plane wave scattering is an important class of electromagnetic problems that is surprisingly difficult to model with the two-dimensional finite-difference time-domain (FDTD) method if the direction of propagation is not parallel to one of the grid axes. In particular, infinite plane wave interaction with dispersive half-spaces or layers must include careful modeling of the incident field. By using the plane wave solutions of Maxwell's equations to eliminate the transverse field dependence, a modified set of curl equations is derived which can model a "slice" of an oblique plane wave along grid axes. The resulting equations may be used as edge conditions on an FDTD grid. These edge conditions represent the only known way to accurately propagate plane wave pulses into a frequency dependent medium. An examination of grid dispersion between the plane wave and the modeled slice reveals good agreement. Application to arbitrary dispersive media is straightforward for the transverse magnetic (TM) case, but requires the use of an auxiliary equation for the transverse electric case, which increases complexity. In the latter case, a simplified approach, based on formulating the dual of the TM equations, is shown to be quite effective. The strength of the developed approach is illustrated with a comparison with the conventional simulation based on an analytic incident wave specification with half-space, single frequency reflection and transmission for the edges. Finally, an example of a possible biomedical application is given and the implementation of the method in the perfectly matched layer region is discussed.     

Scattering Analysis of Dielectric Periodic Structures by an Oblique Incidence

The scattering of dielectric periodic structures by a plane wave incident in the direction oblique to the periodic grooves is analyzed by a method which combines the multimode network theory with the rigorous mode matching method. Combining the TE and TM characteristic mode functions determined in the corresponding 2-D scattering problem resulting from a TE or TM wave incident along the principal-plane of the same structure, and using a simple mathematical transformation, the 3-D scattering problem by an oblique incidence is rigorously solved.     

Oblique scattering from lossy strip structures with one-dimensionalperiodicity

The intentional addition of loss to a periodic structure can be used as a technique to alter its scattering characteristics. The problem of an oblique plane wave incident on an array with one-dimensional periodicity is examined. The unit cell of the array is composed of a number of thin resistive strips. The obliqueness of the incident plane wave combined with the lossy nature of the structure causes the transverse electric (TE) to zˆ and the transverse magnetic (TM) to zˆ fields to couple. To analyze the described problem, two coupled electric field integral equations that have as unknowns the equivalent surface currents on the strips in the unit cell are derived. The integral equations are discretized and solved approximately using the method of moments with subdomain basis and testing functions. The periodic Green's function is efficiently calculated using the Poisson summation formula. The interaction of the structure with the surrounding environment is described in terms of a generalized scattering matrix. Results are presented showing the TE/TM coupling behavior as strip resistance is increased for representative structures     

电磁波在正负折射率介质界面上的传输特性

为了研究负折射率介质这种新型复合材料的电磁性质，利用麦克斯韦电磁理论对电磁波在正、负折射率介质交界面上的反射和透射特性进行了分析。得到了Snell反射定律和折射定律，反射系数和透射系数随入射角的关系（Fresnel公式）。结果发现Snell反射定律和折射定律仍然适用。但折射线与入射线位于法线的同侧；不论是腰波还是TM波，当以某一入射角入射时，反射系数都有可能变为零。这些结果对于设计新型的电磁学和光学器件具有指导性的意义。     

平板光子晶体的全反射遂穿及其偏振特性

为了研究1维平板光子晶体的全反射隧穿效应,采用传输矩阵法进行了TE波和TM波大于全反射角入射1维平板光子晶体时所产生的全反射隧穿效应及其偏振特性的研究。结果表明,TE波和TM波的全反射隧穿峰的频率随平板厚度的增加向低频方向移动;全反射隧穿峰的频率随光子晶体的周期光学厚度的增加而减少。这一结果对认识光子晶体的传输特性是有帮助的。     

杂质吸收对光子晶体缺陷模偏振态的影响

引入复折射率并利用特征矩阵法,研究了杂质的吸收对TE波和TM波缺陷模透射峰的影响.得出:杂质的消光系数对TE波和TM波的缺陷模透射峰都有显著的影响,但对TE波缺陷模的影响比对TM波缺陷模的影响更为明显.当消光系数一定时,TE波的缺陷模透射峰随入射角的增大而迅速减小,而TM波的缺陷模透射峰随入射角的增大而增大.利用这一特性可以设计光子晶体偏振滤波器.     

Radiation properties of a flanged parallel-plate waveguide loadedwith an ε-μ general anisotropic slab

In this analysis, the excitation is taken to be either (1) the lowest-order transverse electric (TE) or the lowest-order transverse magnetic (TM) (i.e. transverse electromagnetic) waves, or (2) a uniform, E- or H-polarized, incident plane wave. As a result of the anisotropy, cross-polarization effects are observed. The formulation of the boundary-value problem is carried out in the Fourier transform domain. Considerable contraction results by using previously developed matrix analysis techniques. In this way, a fruitful integral representation of the tangential components of the magnetic field is first derived in terms of the tangential components of the electric field at the excitation aperture. Next, and after imposing the boundary conditions at the aperture boundary surface, this representation is used as the starting point for a solution on the basis of a moment method (MM) approach using the eigenmodes as basis and weighting functions. Numerical results related to the reflection and coupling coefficients as well as the directive diagrams of the structure are presented in graphical form for various cases     

Spectral and time domain approaches to some inverse scattering problems

Four methods of electromagnetic probing of an inhomogeneous plane stratified medium are presented. They differ by the nature of the incident wave used in the diagnostic. In the first method, the medium is considered as a structure propagating guided modes, and permittivity profiles are determined from the knowledge of one of the guided modes. In the next three, the medium is considered as a scatterer illuminated by a plane wave. Two of them are devoted to reconstruction of conductivity or permittivity profiles from time domain analysis of the reflected field. The last one allows one to obtain permittivity profiles from spectral domain analysis of the reflection coefficient. In spite of their apparent diversity, all these methods are issued from integral representations of the electromagnetic fields. These representations provides the simulated experimental data for the inverse problems. The behavior of these processes has been examined when parameters of practical interest are varied.     

Scattering by a lossy dielectric circular cylindrical multilayer numerical values

The theoretical scattering solution for a plane wave incident normally on a lossy dielectric multilayer circular cylinder of infinite length is outlined. Numerical values of the modal scattering coefficient for TE and TM modes are given for several single and multilayer cylinders. Verifications of the results are described. The values may serve as reference data.     

Comments on `Electromagnetic wave scattering by an infinite planemetallic grating in case of oblique incidence and arbitrarypolarization'

In a previous paper by K. Uchida et al. (see ibid., vol.36, no.3, p.415-22, 1988) it is claimed that in the case of an arbitrary polarized plane wave incident on a strip grating, it is necessary to investigate the quasi-two-dimensional problem where the separation into transverse magnetic (TM) and transverse electric (TE) waves is, in general, impossible. It is shown here that although in general, arbitrarily polarized incident wave case decomposition into TE and TM waves is impossible, it is possible to divide any electromagnetic field into two orthogonal components; (1) fast polarization where an H-field component parallel to the strips is zero and (2) slow polarization where an E-field component parallel to the strips is zero