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In this work, a characterization procedure of Artificial Magnetic Conductor (AMC) metasurfaces based on analytical expressions developed using the Generalized Boundary Conditions (GBCs) model is presented. The correlation between the surface susceptibilities of the PEC scatterers and the main frequency points used in the characterization of AMCs are established. Then the susceptibilities of square patch, square loop, Jerusalem cross and second iteration Minkowski fractal PEC scatterers are obtained by two sets of simulations and are used to calculate profiling frequencies and stability parameters. The detailed characterization procedure is presented and the flexibility and effectiveness of the proposed method are compared to full-wave numerical simulations. [ABSTRACT FROM AUTHOR]

In this work, a design method for artificial magnetic conductor metasurfaces based on generalized boundary conditions is proposed as an alternative to analytic expressions and to conventional optimization approaches. First, the required surface susceptibility is analytically obtained by using generalized boundary conditions and the equivalent circuit model. Then, the geometry of the PEC scatterers is optimized to achieve the required transmission coefficient. The detailed design procedure is presented and its applicability is demonstrated through numerical examples. The proposed method is compared to analytical expressions and to standard optimization methods, showing better results in terms of flexibility and computational cost. Metasurfaces based on square patch, square loop and Jerusalem cross scatterers, mounted on different commercial dielectric substrates are studied for ISM band applications. The results have shown good agreement with the design requirements. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this work is to apply a previously developed ultra weak variational formulation (UWVF) to the solution of the Helmholtz equation in electromagnetic scattering problems. The variational form is based on discontinuous Galerkin with plane wave basis functions in 2‐dimensional finite element mesh. We present a general strategy, which allows to adjust the number of wave directions based on both the element size and the local conditioning number. This provides a cost‐effective mechanism for application of UWVF using nonuniform meshes. Through simulation of scattering of a dielectric‐coated circular cylinder, it is shown that the process significantly improves the UWVF performance. [ABSTRACT FROM AUTHOR]

The choice of the transmission conditions (TCs) across the interfaces between subdomains and its free parameters has a significant impact on the convergence of domain decomposition methods (DDM), especially when applied to propagation and scattering problems. In this paper, we study the convergence behavior of the optimized Schwarz DDM applied to electromagnetic scattering problem in two dimensions for different TCs based on a polynomial approximation of the Dirichlet-to-Neumann map on the Fourier domain. We then propose a methodology to obtain the free parameters of the TC based on the numerical optimization of the spectral radius of the Schwarz iteration matrix on the Fourier domain, taking into account the number of subdomains and some geometrical characteristics such as length and overlap size. To confirm the improvements in convergence, we perform numerical experiments and compare the iteration count for different TCs. [ABSTRACT FROM AUTHOR]

In this paper, Coplanar Waveguide (CPW) elements are used to load UHF RFID meander-line antennas. Although, the insertion of these elements allow to design small antennas their gain decrease depending on the CPW structures are connected. In this sense, a new location to print CPW elements in the meander-line antenna is proposed aiming not to deteriorate the gain. A multi-objective optimization algorithm is applied in the meander-line antennas loaded with CPW elements in different positions and a comparison between their performances is done. To validate the computational model of the proposed antenna its input impedance is measured. [ABSTRACT FROM AUTHOR]

A singular coordinate transformation leads to extreme materials in a transformation-based cloak. If a non-singular transformation is used, the perfect invisibility is lost. The invisibility is also influenced by the homogenization process. In this paper, we investigate these two influences in 2-D circular cylindrical cloaks, obtained from different non-singular mappings. Considering a further deterministic optimization, we also conclude that it is better to use a non-singular cloak based on a mapping scale up to 20%, since it has lower scattering and simpler materials when compared with cloaks based on other mappings. [ABSTRACT FROM AUTHOR]

A possible strategy for avoiding singular material parameters in a transformation-based invisibility cloak involves an out-of-plane stretching, calculated to compensate the in-plane singular transformation. In this paper, we used numerical simulations to analyze the relation among the out-of-plane transformation, the resulting material anisotropy, and the total scattering cross width. Moreover, we show how this information can be used to optimize a cloak with homogeneous anisotropic layers. [ABSTRACT FROM AUTHOR]

In this paper, we solve the \mathcal E and \mathcal B mixed finite element time domain formulation using the alternating-direction implicit (ADI) scheme in time. To save computational cost, the algorithm is improved using a recursive sparsification procedure that approximates the inverse matrix needed to calculate the electric field. Although the method is unconditionally stable, we show that the numerical performance of the algorithm is strongly related to the time step. Numerical results demonstrated that for the same accuracy our approach is much faster than the ADI with Cholesky factorization. [ABSTRACT FROM PUBLISHER]

Reducing the scattering and enhancing the bandwidth (BW) are two desirable aspects in cloak applications. In this paper, we propose their optimization using a simplified objective function, which avoids a costly detailed frequency sweep to get the BW at each iteration. The multi-objective characteristic of our optimization permits us to obtain a set of possible solutions (the Pareto-Front), which represents different compromises between the two objectives. Two examples of dielectric cloaks are presented and discussed. [ABSTRACT FROM PUBLISHER]

ABSTRACT In Part I (W. G. Facco et al., Microwave and Optical Technology Letters 54 (2012) 2709-2716), we introduced the q-version of the nonconforming generalized finite element method (NC-GFEM) for the Helmholtz equation where the interface between the media can be handled as piecewise linear segments. Here we continue the development of the NC-GFEM for Helmholtz where the interface between the media can be handled as piecewise curvilinear. We address: (a) a new scheme of integration to evaluate the integral along the interfaces and (b) the mortar element method (MEM) as a substitute for the Lagrange multipliers. The MEM has the advantage of generating sparse and positive definite systems. Various numerical aspects affecting the NC-GFEM efficiency are analyzed by solving a two-dimensional scattering problem. The convergence of the method is also presented as a function of the number of plane wave directions. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1913-1919, 2014 [ABSTRACT FROM AUTHOR]

To solve wave propagation problems over large domains composed by different media, many authors use the generalized finite element method (GFEM) with a geometrically conforming partition and plane wave enrichment.Such analysis is often accomplished by decomposing the entire domain into several subdomains and performing the analysis individually on each one. Then, the global analysis can be realized by using Lagrange multipliers to ensure the interface constraints. In this article, the GFEM with plane wave enrichment is extended to nonconforming discrete cases where the interface between the media can be handled as piecewise linear segments. Results for problems for which the analytical solution is known are presented to demonstrate the efficiency of the proposed technique. The convergence of the method is also presented as a function of the number of plane wave directions. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2709-2716, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27166 [ABSTRACT FROM AUTHOR]

This paper describes a meshless approach to obtain solutions for propagating microwave problems. The Meshless Local Petrov-Galerkin (MLPG) method is used, based on a local weak form tested with the Heaviside step function. The field is approximated by the Point Interpolation method using radial basis function with additional polynomial basis (RPIMp). TEAM workshop problem 18 is solved and its solution is compared with references from the literature. The results are in good agreement, showing that MLPG can be used as a good alternative to finite elements for this kind of problems. [ABSTRACT FROM PUBLISHER]

This paper presents a methodology based on multiobjective evolutionary optimization and a phase control scheme to design a microwave heating applicator for water sterilization. The optimization problem is formulated in terms of two objective functions: one to maximize the amount of water and the other to minimize the energy spent. The device is modeled as a lossy dielectric multilayer irradiated by two microwave sources. The phase control is done by allowing one of the sources to move. By applying the developed methodology, an efficient applicator is obtained. [ABSTRACT FROM PUBLISHER]

This paper describes an approach to solve the thermal-electromagnetic problem inside a single mode applicator loaded with a ceramic sample. The FEM is combined with analytical techniques to solve the electromagnetic problem. We obtain a fast, simple and accurate method that allows performance investigation of the single mode cavity during the whole heating process. A key feature of the method is to permit iris aperture and short position to vary during the heating. The dependence upon temperature of the complex permittivity of the load is included in the model. The simulation of a thin cylinder ceramic shows that the approach proposed is capable to provide accurate results with low computational cost. [ABSTRACT FROM AUTHOR]

The element-free Galerkin (EFG) meshless method is being widely used in problems where it is difficult to construct a good mesh or remeshing is needed. Although most of these problems include three-dimensional (3-D) domains, few works are found using the EFG in three dimensions in all areas, including electromagnetism. In this paper, we present the formulation and numerical results concerning EFG parameters in a 3-D electromagnetic problem. [ABSTRACT FROM AUTHOR]

This paper describes the integrated use of two design strategies for controlling the permittivity and permeability of a transformation electromagnetics two-dimensional cloak. This hybrid process permits more freedom in the choice of the constitutive properties, which could simplify the implementation with metamaterials. Because simplicity of materials and scattering performance are inherently conflicting characteristics, a multi-objective genetic algorithm is applied to optimize them. According to the presented results for a transverse-magnetic layered cloak, it is possible to have a good performance in terms of scattering even with an approximated reduced set of parameters with unitary axial permeability. [ABSTRACT FROM AUTHOR]

The classical numerical methods for the simulation of wave propagation phenomena in multiscale systems can demand an unnecessary computational cost. This study proposes a multiclass strategy to be applied to the linear multistep time integration methods in the formalism of the discontinuous Galerkin (DG) space discretisation. The multiclass scheme is applied specifically to linear multistep strong stability preserving method (SSPMS). The potential of this strategy is demonstrated by numerical tests applied to two electromagnetic problems. The results show that the proposed schemes promote a significant improvement compared with the standard SSPMS and the fourth‐order Runge–Kutta. Furthermore, in order to obtain a real speed up, this study presents a class parameter that produces a previous knowledge to determine the number of classes. [ABSTRACT FROM AUTHOR]

A frequency selective surface (FSS) composed of a periodic arrangement of meander line inclusions is numerically analysed. The study is presented with respect to the number of meanders and is a generalization of the U-shape (1-meander). A y-polarized incident wave is used to illuminate the structure. The results are obtained by the finite element method. By investigating the transmission coefficient, in this letter, it is seen that several stopbands may be exhibited within the operating frequency band and resonant frequency reduction can be associated with the number of meanders. For an incident wave with linear polarization, our findings suggest that the shift at the resonant frequency is also due to the increase in the effective length in the polarization direction of the incident wave. The validation of our model is performed by U-shape simulation already experimentally tested in other letters. A very good agreement has been achieved. [ABSTRACT FROM AUTHOR]

The generalized finite-element method (GFEM) enriched by plane waves has been proved suitable to solve the 2-D Helmholtz equation. However, when the number of unknowns increases, some difficulties arise, such as bad condition number. Therefore, developing a pre-processing methodology to identify an appropriate number of degrees of freedom for each problem could be useful. This paper presents a systematic approach to determine the optimal number of plane waves for each problem to be used in GFEM solution. It is based on the analysis of the traditional FEM solution with a poor mesh resolution using the fast discrete curvelet transform. The results indicate that the adopted strategy can guarantee accurate and converging responses for GFEM in complex problems, along with remarkable reductions of the computational cost. [ABSTRACT FROM AUTHOR]

This paper addresses the generalized finite-element method enriched by plane waves for the 2-D Helmholtz equation. The enrichment function is modified to reduce the effect of numerical dispersion from coarse meshes and to make it possible to treat essential boundary conditions in a straightforward way. Two numerical examples, the free space propagation problem and the plane wave scattering by a cylinder, demonstrate the effectiveness of the new enrichment function. [ABSTRACT FROM PUBLISHER]

A new numerical discretization of the complex frequency shifted-perfectly matched layer (CFS-PML) is presented for truncation of open domains. This discretization is based on the theory of discrete differential forms applied to electromagnetism, which guarantees both the simplification of the algorithms and a more elegant formulation of expression. The curl Maxwell's equations are solved in time domain in terms of electric e magnetic fields. The Ampere-Maxwell law with, the constitutive relations included through the Hodge operator, is discretized in space by applying the Galerkin method. Conversely, the Faraday law is represented by topological relations via incidence matrix. The time domain discretization uses the leap-frog scheme with a recursive convolution inside PML region. Two examples are shown, the first one to validate the CFS-PML procedure and the second one to solve a typical ground penetrating radar scenario which include a lossy media. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:351-357, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27298 [ABSTRACT FROM AUTHOR]

The meshless local Petrov--Galerkin method (MLPG) with a mixed formulation to impose Dirichlet boundary conditions is investigated in this paper. We propose the use of Shepard functions for inner nodes combined with the radial point interpolation method with polynomial terms (RPIMp) for nodes over the Dirichlet boundaries. Whereas the Shepard functions have lower computational costs, the RPIMp imposes the essential boundary conditions in a direct manner. Results show that the proposed technique leads to a good tradeoff between computational time and precision. [ABSTRACT FROM AUTHOR]

An out-of-plane coordinate transformation can avoid singular materials in a two-dimensional electromagnetic cloak. Based on numerical simulations of elliptical cylinders, in this paper we show that the use of two different constants to define the out-of-plane stretching can result in anisotropic materials with lower values and yet with a better scattering reduction for a given incident wave direction. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a systematic methodology to aid design a low-cost patch antenna for RFID readers. The geometric antenna parameters are found using multiobjective optimization for return loss minimization and gain maximization. To assess the use of low-cost FR-4 substrate the radiation efficiency has been investigated using software simulations. A prototype antenna was built and its parameters were measured in the anechoic chamber. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:905-908, 2016 [ABSTRACT FROM AUTHOR]

Nonconforming point interpolation method (NPIM) is a meshless method that has been applied to problems in mechanics in the last years. In this paper, we investigate NPIM in electromagnetism. We present its formulation and shape functions, which are generated by the radial point interpolation method with polynomial terms. The numerical results are compared to the ones obtained by the finite flement method (FEM) and the element-free Galerkin method (EFG). [ABSTRACT FROM PUBLISHER]

We propose a Multiobjective Clonal Selection Algorithm (MCSA) with dynamic variation of its main parameters for the solution of engineering design problems. The MCSA performs a cloning process using different probability distributions, in which the mutation strengths are guided based on a logarithmic rule and on information implicitly created by a simple differential evolution technique. This feature results in a self-adapting search in the algorithm. The efficiency of the MCSA is studied comparing its performance with the Nondominated Sorting Genetic Algorithm II (NSGA-II) in analytical test problems and also in the design of a microwave heating device. The MCSA has outperformed the NSGA-II in all problems investigated. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of mobile robot navigation using artificial potential fields. Many potential field based methodologies are found in the robotics literature, but most of them have problems with spurious local minima, which cause the robot to stop before reaching its target position. Although some free of local minima methodologies are found in the literature, none of them are easy to implement and generalize for complex shaped environments and robots. We propose a perfect analogy between electrostatic field computation and robot path planning. Thus, an easy solution to the problem, which is based on standard finite-element methods, can be applied with generic geometries and can even take into account the robot's orientation. To demonstrate the elegance of the proposed methodology, several experimental results with actual mobile robots are included. [ABSTRACT FROM AUTHOR]

The element-free Galerkin method (EFG) has specific characteristics that require the usage of techniques and data structures in order to provide efficient calculation. This paper address two problems concerning the EFG implementation. The point location problem, which must find in which subdomain the integration point is located, and the influence domain problem, which must find the nearest nodes to build an influence domain and construct the shape functions. This work proposes the use of new data structures and algorithms in order to solve these problems, speeding up the method and providing a fast and correct influence domain construction. [ABSTRACT FROM AUTHOR]