Approximate boundary conditions
TL;DR: Approximate boundary conditions are a means for simulating material and surface effects in scattering and propagation as discussed by the authors, and criteria for their validity are given for the validity of these conditions.
Abstract: Approximate boundary conditions are a means for simulating material and surface effects in scattering and propagation. A number of conditions are discussed, and criteria are given for their validity.
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TL;DR: In this paper, the reflection properties of multiple electric/magnetic Salisbury screens have been studied and it is shown that relatively large reductions in specular reflection are possible over sizeable bandwidths using relatively few Salisbury screen screens.
Abstract: The reflection properties of multiple electric/magnetic Salisbury screens have been studied. Analytical formulae are developed for the maximally flat design of two- and three-screen planar stackups that have taken into account appropriate values for the spacer materials used to separate the screens. The effect of curvature has also been assessed. It is shown that relatively large reductions in specular reflection are possible over sizeable bandwidths using relatively few Salisbury screens. Furthermore, these reductions are not completely destroyed if the incident wave is not normal to the surface, if the surface is curved or if there are errors in fabrication of the screen. >
662 citations
TL;DR: In this paper, the authors proposed the concept of metasurface waves (M-waves) and provided a general theory to describe the principles of them and showed that the M-waves share some fundamental properties such as extremely short wavelength, abrupt phase change and strong chromatic dispersion, which make them different from traditional bulk waves.
Abstract: Metasurfaces are artificially structured thin films with unusual properties on demand. Different from metamaterials, the metasurfaces change the electromagnetic waves mainly by exploiting the boundary conditions, rather than the constitutive pa-rameters in three dimensional (3D) spaces. Despite the intrinsic similarities in the operational principles, there is not a universal theory available for the understanding and design of metasurface-based devices. In this article, we propose the concept of metasurface waves (M-waves) and provide a general theory to describe the principles of them. Most importantly, it is shown that the M-waves share some fundamental properties such as extremely short wavelength, abrupt phase change and strong chromatic dispersion, which make them different from traditional bulk waves. It is shown that these properties can enable many important applications such as subwavelength imaging and lithography, planar optical devices, broadband anti-reflection, absorption and polarization conversion. Our results demonstrated unambiguously that traditional laws of diffraction, refraction, reflection and absorption should be revised by using the novel properties of M-waves. The theory provided here may pave the way for the design of new electromagnetic devices and further improvement of metasurfaces. The exotic properties of metasurfaces may also form the foundations for two new sub-disciplines called “subwavelength surface electromagnetics” and “subwavelength electromagnetics”.
396 citations
TL;DR: A broadband infrared absorber is proposed by engineering the frequency dispersion of metamaterial surface (metasurface) to mimic an ideal absorbing sheet by demonstrating a polarization-independent absorber with absorption larger than 97% and the concept of dispersion engineering may provide helpful guidance for the design of a broadband absorber.
Abstract: We propose a broadband infrared absorber by engineering the frequency dispersion of metamaterial surface (metasurface) to mimic an ideal absorbing sheet. With a thin layer of structured nichrome, a polarization-independent absorber with absorption larger than 97% is numerically demonstrated over a larger than one octave bandwidth. It is shown that the bandwidth enhancement is related with the transformation of the Drude model of free electron gas in metal film to the Lorentz oscillator model of a bound electron in the structured metallic surface. We believe that the concept of dispersion engineering may provide helpful guidance for the design of a broadband absorber.
245 citations
TL;DR: Some of the tools used in computational electromagnetics are placed into perspective with respect to the different kinds of approaches that may be used and their computer-resource requirements.
Abstract: Some of the tools used in computational electromagnetics are placed into perspective with respect to the different kinds of approaches that may be used and their computer-resource requirements. Particular attention is paid to numerical models based on integral and differential equations. After a brief background discussion, some of the analytical and numerical issues involved in developing a computer model are reviewed. Some practical considerations are included from the viewpoint of computer-resource requirements, followed by a discussion of some ways by which computer time might be reduced. The presentation concludes with a brief examination of validation and error checking. The emphasis throughout is on review and summarization rather than detailed exposition. >
198 citations
TL;DR: In this article, a generalized form of the method-of-moments technique is presented for a diverse class of arbitrarily shaped three-dimensional scatterers, which may be totally or partially penetrable.
Abstract: We outline a generalized form of the method-of-moments technique. Integral equation formulations are developed for a diverse class of arbitrarily shaped three-dimensional scatterers. The scatterers may be totally or partially penetrable. Specific cases examined are scatterers with surfaces that are perfectly conducting, dielectric, resistive, or magnetically conducting or that satisfy the Leontovich (impedance) boundary condition. All the integral equation formulations are transformed into matrix equations expressed in terms of five general Galerkin (matrix) operators. This allows a unified numerical solution procedure to be implemented for the foregoing hierarchy of scatterers. The operators are general and apply to any arbitrarily shaped three-dimensional body. The operator calculus of the generalized approach is independent of geometry and basis or testing functions used in the method-of-moments approach. Representative numerical results for a number of scattering geometries modeled by triangularly faceted surfaces are given to illustrate the efficacy and the versatility of the present approach.
197 citations
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TL;DR: This work develops a systematic method for obtaining a hierarchy of local boundary conditions at these artifical boundaries that not only guarantee stable difference approximations, but also minimize the (unphysical) artificial reflections that occur at the boundaries.
Abstract: In practical calculations, it is often essential to introduce artificial boundaries to limit the area of computation. Here we develop a systematic method for obtaining a hierarchy of local boundary conditions at these artifical boundaries. These boundary conditions not only guarantee stable difference approximations, but also minimize the (unphysical) artificial reflections that occur at the boundaries.
2,648 citations
TL;DR: In this article, the exact electromagnetic boundary conditions at the surface of a material of large refractive index can be approximated to yield the usual impedance or Leontovich boundary conditions, which are valid for surfaces whose radii of curvature are large compared with the penetration depth.
Abstract: It is shown how the exact electromagnetic boundary conditions at the surface of a material of large refractive index can be approximated to yield the usual impedance or Leontovich boundary conditions. These conditions relate the tangential components of the electric and magnetic fields (or the normal components and their normal derivatives) via a surface impedance which is a function only of the electromagnetic properties of the material. They are valid for surfaces whose radii of curvature are large compared with the penetration depth, and also for materials which are not homogeneous but whose properties vary slowly from point to point. As the refractive index (or conductivity) increases to infinity, the conditions go over uniformly to the conditions for perfect conductivity.
323 citations
TL;DR: In this article, an approximate equivalence between an impedance loaded surface and a thin dielectric shell is given, which is used to compute the backscattering from a thin circular dielectron and the results are compared to the exact solution.
Abstract: An approximate equivalence between an impedance loaded surface and a thin dielectric shell is given. This approximation is used to compute the backscattering from a thin circular dielectric tube and the results are compared to the exact solution. Computations for backscattering from a thin dielectric cone-sphere and resonant wire loop inside of a thin dielectric cylinder are also given as further illustrations of the method.
186 citations
TL;DR: In this article, a pair of Wiener-Hopf integral equations are derived from which to determine the electric and magnetic currents present in the sheet, and the solutions of these equations are deduced by symmetry considerations.
Abstract: In spite of the considerable attention which has been focused on diffraction by perfectly conducting structures, little success has so far been achieved when finite conductivity is introduced. It is now shown that with the assumption of suitable boundary conditions, the problem of diffraction at a metal sheet is capable of exact solution. Corresponding to each of two fundamental polarizations, a pair of Wiener-Hopf integral equations is derived from which to determine the electric and 'magnetic' currents present in the sheet. One of these equations is subjected to a rigorous solution, and from it the solutions of the other three are deduced by symmetry considerations. Use of the generalized method of steepest descent then serves to determine the diffracted fields. The case of a circularly polarized incident wave is also briefly discussed and a comparison presented between the theoretical and experimental forms of the scattered field; good agreement is obtained.
149 citations
TL;DR: In this article, the surface field and far field of a resistive strip for a variety of strip widths w and uniform resistances R were obtained using the moment method applied to an appropriate integral equation.
Abstract: Strips made of a resistive sheet material have lower backscattering cross sections than the corresponding perfectly conducting strips, and this is true in particular when the illumination is edge-on with the electric vector parallel to the edge. Attention is focused on this case. Using the moment method applied to an appropriate integral equation, data are obtained for the surface field and backscattered far field of a resistive strip for a variety of strip widths w and uniform resistances R . The front- and rear-edge contributions to the far field are then extracted. It is shown that for strips whose width is greater than about a half-wavelength the former is the same as for a half-plane having the same resistance, whereas the latter is proportional to the square of the current at that point on the half-plane corresponding to the rear edge of the strip. The implications of these results on the selection of a strip resistance for low backscattering are discussed.
84 citations