多层介质涂覆结构的高阶张量阻抗边界条件

对于多层复杂介质涂敷的导体表面，用谱域法给出介质与空气界面处的谱域精确阻抗表达式，对将其变换至空域任意阶阻抗边界条件的方法的可行性进行分析，并引入优化方法，成功地得到空域任意阶张量阻抗边界条件。通过算例说明，对于多层复杂介质涂敷、低反差介质涂敷以及厚涂敷的情形，采用优化方法导出任意阶阻抗边界条件简单、可行。     

Generalised impedance boundary conditions for EM scatteringproblems

Generalised impedance boundary conditions (GIBC) are derived for a planar, homogeneous, magnetic dielectric slab grounded by a perfect electric conducting plane. These boundary conditions, which are expressed in terms of linear differential operators of infinite order, reduce to the Weinstein boundary conditions in the limiting case of small thickness of the dielectric slab     

Generalized impedance boundary conditions in scattering

The authors present generalized surface impedance conditions that improve medium characterization. One of the most common conditions that is often used to simulate a dielectric coating is the standard impedance boundary condition, and the improved boundary condition discussed can be viewed as a generalization of this, distinguished by the presence of higher-order derivatives of the field. By virtue of the derivatives, the conditions are less local in character, and the additional degrees of freedom can be used to better simulate the material properties of a surface. Following a review of the standard impedance condition, the new conditions are introduced. Several forms are presented, each with coefficients which are functions of the geometry and material properties of the surface. The applications of these to a variety of scattering problems are then discussed     

Higher order impedance boundary conditions for sparse wire grids

Higher order impedance boundary conditions designed for modeling wire grids of thin conducting wires are established. The derivation is based on the exact analytical summation of the individual wire fields. This allows one to write an approximate boundary condition on the grid surface, which connects the averaged electric field and the averaged current (or the electric field and the averaged magnetic fields on the two sides of the grid surface). The condition depends on the tangential derivatives of the averaged current (up to the sixth order). This approach provides an extension of the averaged boundary conditions method (well established for dense grids) to sparse grids. Numerical examples demonstrate very good accuracy of the solutions for the field reflected from grids with the wire separation as large as half of the wavelength     

高阶各向异性阻抗边界条件的导出

在求解各向异性介质涂敷物体的电磁散射中 ,采用高阶各向异性阻抗边界条件可以简化求解过程 ,提高近似解的精度。文中采用谱域法导出各向异性介质涂敷平面的二阶张量阻抗边界条件 ,并通过例子证明其精确性。     

Higher order impedance and absorbing boundary conditions

Traditionally, generalized impedance boundary conditions (GIBCs) have been used to model dielectrics and coated surfaces, and absorbing boundary conditions (ABCs) have been used to simulate nonreflecting surfaces. The two types have the same mathematical form and, in most instances, a higher order condition involving higher order field derivatives has a better accuracy. We demonstrate that there is a close connection between the two and this enables us to use a systematic method which is available for generating GIBCs of any desired order to derive new two- and three-dimensional ABCs. The method is applicable to curvilinear/doubly-curved surfaces and examples are given. Finally, curves are presented that quantify the accuracy of two-dimensional ABCs up to the fourth order, and show how higher order ABCs can improve the efficiency of large scale partial differential equation (PDE) solutions     

On combined source solutions for bodies with impedance boundary conditions

Numerical solutions to the impedance boundary condition (IBC) combined source integral equation (CSIE) for scattering from impedance spheres are presented. The CSIE formulation is a well-posed alternative to the IBC electric and magnetic field integral equations which can be contaminated by spurious resonant modes. Compared with the IBC combined field integral equation (CFIE), CSIE solutions have the same accuracy when the combined source coupling admittance is chosen to be the same value as the combined field coupling admittance. However, the CSIE formulation is better suited than the CFIE for creating a general purpose computer code capable of handling aperture radiation problems and/or a scatterer which has a spatially varying surface impedance.     

Two-dimensional diffraction by a wedge with impedance boundary conditions

The two dimensional problem of diffraction by a wedge with impedance boundary conditions on its faces is explicitly solved in a form that admits effective numerical simulation by simple perfectly scalable algorithms with unlimited capability for parallel processing. The solution is represented as a superposition of the geometric field that is completely determined by elementary ray analysis and of the waves diffracted by the tip of the wedge. The diffracted field is explicitly represented as a mathematical expectation of a specified functional on trajectories of a random motion determined by the configurations of the problem and by the boundary conditions. The numerical results confirm the efficiency of this approach.     

Surface impedance boundary conditions at oblique incidence in FDTD

Surface impedance formalism permits to reduce the discretization volume in a finite difference time domain (FDTD) code. The method based on the definition of surface impedances for plane waves at horizontal or vertical polarizations, is introduced in fdtd algorithm, to model interfaces between two media. In this paper, two dimensional and three dimensional results are compared to those computed with classical fdtd or Fresnel reflection coefficients involving a Fourier transform.     

Curvature corrected impedance boundary conditions in an arbitrary basis

We present a generalization of the Rytov analysis for curvature corrections to the impedance boundary condition (IBC) that allows such boundary conditions to be written down using general coordinate systems and bases for vectors. This removes the need to base the analysis of IBCs on either principal curvature axes or on hypothetical orthogonal coordinate systems. As an application, we show how to write down high-order IBCs for surfaces that are the deformation of a plane. We also show how the use of such an IBC can be used to further reconcile Kirchhoff and small perturbation methods.     

Scattering by superquadric dielectric-coated cylinders using higherorder impedance boundary conditions

A general method for deriving higher order impedance boundary conditions is described. It is based on solving an appropriate canonical problem exactly in the spectral domain. After approximating the spectral impedance terms as a ratio of polynomials in the transform variable, elementary properties of the Fourier transform are used to obtain the corresponding boundary condition in the spatial domain. The method is applicable to multilayer coatings with arbitrary constitutive relations. Higher-order boundary conditions which neglect the effects of curvature are derived for a dielectric coating using the method. The boundary condition equation and the magnetic field integral equation are solved simultaneously using the method of moments, yielding the bistatic and monostatic radar cross section for dielectric-coated superquadric cylinders. The method is also applicable to a combined field integral equation (CFIE) solution, which can be used to eliminate the internal resonance problem associated with either the electric field integral equation (EFIE) or magnetic field integral equation (MFIE)     

Matrix formulation of corrugated feeds by using impedance boundary conditions

Scattering from bodies of revolution with anisotropic and arbitrary boundary conditions is formulated. It is shown that the effect of impedance boundary conditions is to modify only the diagonal elements of the characteristic matrix of the object for the numerical solution. Application to corrugated feeds and consequent simplification of the characteristic matrix, owing to corrugation geometry, are also discussed.     

Investigation of scattering by corrugated structures using impedance boundary conditions

The usefulness of impedance boundary conditions for the investigation of field problems concerning corrugated surfaces is studied by its application to the scattering by a partially corrugated conducting prism. The corrugated portion of the prism is represented by an impedance surface and the behaviour of the surface currents and the scattered fields are examined. The results are also compared with available data on a similar problem.     

Transient response computation of spheroidal objects using impedance boundary conditions

The transient response of imperfectly conducting and permeable spheroidal objects is determined using the impedance boundary conditions. Since the impedance boundary conditions are not known in the time domain, the frequency domain analysis is used to formulate the problem. The use of impedance boundary conditions relates conveniently the solution to the object's physical parameters and simplifies the computations. For highly conducting objects a simplified method is used to determine numerically the frequency domain data, which utilizes the numerical code for perfectly conducting objects. The excitation is assumed to be due to a periodic pulse train and generated by a small circular loop antenna. The procedure for the computation of the transient response, at very low excitation frequencies, is presented and the response forms for different object parameters and orientations are computed.     

Effective impedance boundary conditions for an inhomogeneous thinlayer on a curved metallic surface

Effective impedance boundary conditions for an inhomogeneous thin layer coated on a perfectly conducting object are considered. The permittivity of the thin layer is inhomogeneous along both the normal and tangential directions. Explicit forms of the first- and second-order approximate impedance boundary conditions are derived first for a two-dimensional (2D) thin layer for the TE and TM cases. Numerical results are presented. The case of Maxwell's equations for a three-dimensional inhomogeneous thin layer is also considered     

Exact surface impedance/admittance boundary conditions for complexgeometries: theory and applications

A methodology useful to derive exact and higher order surface impedance/admittance boundary conditions (HOI/ABC's) for complex geometries is presented. It is shown that exact surface boundary conditions are always expressed through dyadic integral operators involving the tangential magnetic and electric fields all over the surface of the body. Quasi-local surface boundary conditions that include curvature effects are shown to be computable through an asymptotic approximation of the integral operators. Finally, an example of a surface admittance boundary condition useful to analyze a structure exhibiting discontinuities along its surface boundary is presented. Practical examples to demonstrate the feasibility of the proposed methodology, as well as the accuracy of the resulting surface boundary conditions are also presented     

FDTD surface impedance model for coated conductors

A new finite-difference time-domain (FDTD) model of dielectric and conductive layers on conductive surfaces is developed. The model is based on surface impedance boundary condition, allowing the coating and the conductive backing to be removed from the computational space. The proposed model extends the previous FDTD models, which are formulated for coatings on perfect electric conductors (PEC), to coatings on more general dielectric and conductive materials. On the other hand, the model can also be regarded as a generalization of models designed for conductors without coatings. The present model accounts for the first thickness resonance of the layer by modeling the singularity of the tangent function appearing in the impedance function. The proposed model is numerically verified for normal incidence in the frequency domain and for varying oblique angles of incidence in the time domain by comparison with analytical results.     

Generalised boundary conditions for a material sheet with both sides coated by a dielectric layer

Many structures which play important roles in practical applications involve planar sheets coated with dielectric layers. In order to avoid the mathematical difficulties arising from this type of multilayered structures in antennas and propagation problems one tries to replace the coated sheet by an equivalent hypothetical plane having appropriate boundary conditions. A new and general method capable of obtaining these generalised boundary conditions is presented and applied to three important particular cases where the structure consists of a resistive or conductive or impedance plane with both faces coated with dielectric layers.<>     

Higher order impedance boundary conditions applied to scattering bycoated bodies of revolution

In this paper higher order impedance boundary conditions will be employed in the solution of scattering by coated conducting bodies of revolution. The higher order impedance solution reduces the total number of unknowns relative to the exact solution, and produces a system matrix which is less dense than that of the exact solution. The construction of the solution involves two distinct steps. In the first step the body of revolution is replaced by an equivalent set of electric and magnetic currents on its exterior surface which generate the true fields outside the body. An integral equation relating these currents through the free space Green's function is derived. Step two employs the higher order impedance boundary condition to relate the electric and magnetic currents on the surface of the body. This replaces the rigorous solution of the interior problem. The higher order impedance boundary conditions are derived by obtaining an exact impedance boundary condition in the spectral domain for the coated ground plane, approximating the impedances as ratios of polynomials in the transform variables, and employing the Fourier transform. The resulting spatial domain differential equations are solved in conjunction with the integral equation using the method of moments. Several examples of bistatic and monostatic radar cross section for coated bodies of revolution are used to illustrate the accuracy of the higher order impedance boundary condition solution relative to the standard impedance boundary condition solution and the exact solution. The effects of coating thickness, loss, and curvature on the accuracy of the solution are discussed     

A multilayer coated fiber-based substrate suitable for printed functionality

A recyclable multilayer coated fiber-based substrate combining sufficient barrier and printability properties for printed functional devices was developed using reel-to-reel techniques. The substrate consists of a mineral pigment layer coated on top of a barrier latex layer. The pigment layer allows controlled absorption of ink solvents. By adjusting the thickness and porosity of the top coating the printability can be tuned for various functional inks. As a proof of concept a hygroscopic insulator field effect transistor (HIFET) was successfully printed on the multilayer-coated paper.