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The purpose of this paper is to calculate near field and far field scattering of SH waves by multiple multilayered anisotropic circular inclusions using parallel volume integral equation method (PVIEM) quantitatively.

The PVIEM is applied for the analysis of elastic wave scattering problems in an unbounded solid containing multiple multilayered anisotropic circular inclusions. It should be noted that this numerical method does not require the use of the Green’s function for the inclusion – only the Green’s function for the unbounded isotropic matrix is needed. This method can also be applied to solve general elastodynamic problems involving inhomogeneous and/or anisotropic inclusions whose shape and number are arbitrary.

A detailed analysis of the SH wave scattering problem is presented for multiple multilayered orthotropic circular inclusions. Numerical results are presented for the displacement fields at the interfaces and the far field scattering patterns for square and hexagonal packing arrays of multilayered circular inclusions in a broad frequency range of practical interest.

To the best of the authors’ knowledge, the solution for scattering of SH waves by multiple multilayered anisotropic circular inclusions in an unbounded isotropic matrix is not currently available in the literature. However, in this paper, calculation of displacements on interfaces and far field scattering patterns of multiple multilayered anisotropic circular inclusions using PVIEM as a pioneer of numerical modeling enables us to investigate the effects of single/multiple scattering, fiber packing type, fiber volume fraction, single/multiple layer(s), the multilayer’s geometry, isotropy/anisotropy and softness/hardness.

The purpose of this paper is to compare exact and Physical‐Optics‐approximated results of the electromagnetic field scattered by a perfectly conducting semi‐infinite elliptic cone illuminated by a plane wave. The results are important for judging the reliability of Physical‐Optics based field estimations of electrically large environments which include tip‐like structures (e.g. airport scenarios).

The spherical‐multipole analysis is applied to determine the exact total field outside a perfectly conducting semi‐infinite elliptic cone. The underlying boundary‐value problem is solved by a separation of variables of the Helmholtz equation in sphero‐conal coordinates leading to a two‐parametric eigenvalue problem with two coupled Lamé differential equations. The exact scattered far field is determined from the exact surface current on the cone using a bilinear expansion of the dyadic Green's function. The Physical‐Optics (PO) field is evaluated similarly starting from a surface current which is directly found from the incident magnetic field.

The diffraction coefficients of the exact scattered field and the PO scattered field are compared for different parameters (polarization and angle of incidence) of the plane wave. Reasonably well corresponding results are obtained for those angles of incidence of the plane wave where the entire cone is illuminated, otherwise the error of the PO approximation is increasing not just in the shadow region.

If carefully applied, the Physical‐Optics method can be useful and sufficient to obtain fields scattered by cone‐like structures.

Nowadays, nano-antennas or nanoscale absorbers made by innovative materials such as carbon nanotubes are gaining more and more interest, because of their outstanding features. The purpose of this paper is to investigate the scattering properties of carbon nanotubes, either isolated or arranged in arrays. The peculiar behaviour of such innovative materials is studied, taking also into account the finite length of the structure and the dependence of the scattering field from the operating temperature.

First a model is presented for the electrical transport along the carbon nanotubes, based on Boltzmann quasi-classical transport theory. The model includes quantistic and inertial phenomena observed in the carbon nanotube electrodynamics. The model also includes the effects of temperature. Using this electrodynamical model, the electromagnetic formulation of the scattering problem is cast in terms of a Pocklington-like equation. The numerical solution is obtained by means of the Galerkin method, with special care in handling the logarithmic singularity of the kernel. Case studies are carried out, either referred to isolated single-wall carbon nanotubes (SWCNTs) and array of SWCNTs.

The scattering properties of SWCNT are strongly influenced by the temperature and by the distance between the tubes. As temperature increases, the amplitude of the resonance peaks decreases, at a rate which is double the rate of changes of temperature. The resonance frequencies are insensitive to temperature. As for the distance between the tubes in an array, it influence the scattering resonance introducing a shift in the resonance frequencies which is appreciable for distances lower than the semi-length of the CNT. For higher distances the CNT scattered field may be regarded as the sum of the fields emitted by each CNT, as if they were isolated.

As far as now only SWCNTs have been studied. The multi-wall carbon nanotubes would show a richer behaviour with temperature, due to the joint effect of reduction of the mean free path and increase of the number of conducting channels, as temperature increases.

Possible use of carbon nanotubes as absorbing material or scatterers.

The model presented here is based on a self-consistent and physically meaningful description of the CNT electrodynamics, which takes rigorously into account the effect of temperature, size and chirality of each CNT.

This paper deals with the inverse scattering problem of reconstructing the material properties of perfectly conducting or dielectric cylindrical objects. The material properties are reconstructed from measured far‐field scattering data provided by the Electromagnetics Technology Division, AFRL/SNH, 31 Grenier Street, Hanscom AFB, MA 01731‐3010. The measured data have to be calibrated for use in our reconstruction algorithm. The inverse scattering problem formulated as unconstrained nonlinear optimization problem is numerically solved using an iterative scheme with a variable calibration factor which will be determined during the optimization process. Numerical examples show the successful application of the method to the measured data.

The majority of first-principle, homogenisation techniques makes use of the dipole terms of a small particle radiation, and, consequently, the respective dipole polarisabilities. This paper aims to take the next step and propose a new systematic technique for extracting the quadrupolarisability of planar metamaterial scatterers.

Firstly, it is assumed that the particle, under study, can be modelled as a set of dipole and quadrupole moments, and by utilising the respective polarisabilities, the far-field response of the scatterer is calculated. Then, the far-field scattering field of the particle is constructed in terms of the dipole and quadrupole moments, which, in turn, are expressed as a function of the unknown polarisabilities. Finally, the desired polarisabilities are retrieved by a system of equations, which involves numerically derived electric field values at specific positions around the scatterer.

The quadrupolarisability of planar metamaterial particles is extracted, through an easy to use, yet very accurate and efficient methodology. Moreover, the proposed technique is verified via comprehensive comparisons of consequently computed and simulated total radiated power values, which reveal its advantages and applicability limits. Finally, the total radiation power contribution of each calculated, individual multipole is provided, to further investigate the radiation mechanism of all nano-particles under study.

The initial and most important step of extracting a single quadrupolarisability of a planar realistic nano-particle has been performed, herein, for the first time. The addition of the respective quadrupole in the scattering model, shifts the multipole approximation limit upwards in terms of frequency, and, therefore, nano-particles with quadrupole resonances can, now, be precisely represented via polarisabilities for various metamaterial or metasurface applications.

The purpose of this study is to introduce a novel method for the measurement of electromagnetic material parameters.

The main idea behind the approach is the fact that for slabs with elongated shapes, the intensity of the backscattered field and the electromagnetic resonance frequency corresponding to the length of the sample are dependent on the conductivity of the sample’s material.

It is shown that for a known scattered field and resonance frequency, it is possible to formulate an inverse problem as to the calculation of the conductivity of the sample’s material at the considered frequencies. To investigate the applicability of the method, demonstrative experiments are performed during which the micro-Doppler effect is used to increase the measurement accuracy. The idea is extended to the case of anisotropic samples, with slight modifications proposed to the experimental setup in the case of significant anisotropy in the investigated material.

The measurement method may prove useful for the investigation of the high-frequency conductive properties of certain materials of interest.

To the best of the authors’ knowledge, this is the first time the use of the micro-Doppler effect is proposed for the purpose of the measurement of material parameters.

The purpose of this paper is to numerically investigate time-harmonic elastic wave propagation with the analysis of effective wave velocities and attenuation coefficients in a three-dimensional elastic composite consisting of infinite matrix and uniformly distributed soft, low-contrast and absolutely rigid disc-shaped micro-inclusions.

Within the assumptions of longitudinal mode of a propagating wave as well as dilute concentration and parallel orientation of inclusions in an infinite elastic matrix, Foldy’s dispersion relation is applied for introducing a complex and frequency-dependent wavenumber of homogenized structure. Then, the effective wave velocities and attenuation coefficients are directly defined from the real and imaginary parts of wavenumber, respectively. Included there a far-field forward scattering amplitude by a single low-contrast inclusion given in an analytical form, while for the other types of single scatterers it is determined from the numerical solution of boundary integral equations relative to the displacement jumps across the surfaces of soft inclusion and the stress jumps across the surfaces of rigid inclusion.

On the frequency dependencies, characteristic extremes of the effective wave velocities and attenuation coefficients are revealed and analyzed for different combinations of the filling ratios of involved types of inclusions. Anisotropic dynamic behavior of composite is demonstrated by the consideration of wave propagation in perpendicular and tangential directions relatively to the plane of inclusions. Specific frequencies are revealed for the first case of wave propagation, at which inclusion rigidities do not affect the effective wave parameters.

This paper develops a micromechanical study that provides a deeper understanding of the effect of thin-walled inclusions of diversified rigidities on elastic wave propagation in a three-dimensional composite. Described wave dispersion and attenuation regularities are important for the non-destructive testing of composite materials by ultrasonics.

The purpose of this paper is to derive the dyadic representations of Green’s function in lossy medium because of the electric current dipole source radiating in close proximity of a PEC wedge and to reveal the effect of conductivity on the scattered electric field.

By using the scalarization procedure, the paraxial fields are obtained first and then scalar Green’s functions are used to derive asymptotic forms of the dyadic Green’s functions. The problem is also analyzed by the image theory and analytical derivations are compared. However, analytically calculated results are validated with FEKO, a commercially available numerical electromagnetic field solver.

The results indicate that excellent agreement is observed between analytical and numerical results. Moreover, it is found that the presence of conductivity introduces a reduction in scattered electric fields.

Asymptotically derived forms presented in this study can be used to calculate field distributions in the paraxial region of a wedge in a lossy medium.

Analysis of the frequency selective surface (FSS) is of great significance. In the method of moments, when the electric size of the FSS increases, huge in-core memory and CPU time are required. The purpose of this paper is to efficiently analyze the finite FSS backed by dielectric substrate utilizing sub-entire-domain (SED) basis function method.

Different types of SED basis functions are generated according to the locations of the cells in the entire structure, and a reduced system is constructed and solved. The couplings of all cells of the FSS are taken into account by using Green’s function and Galerkin’s test procedure. The spatial Green’s function is obtained with the discrete complex image method. The reflection and transmission coefficients of the FSS are calculated using the far field of the FSS and the metallic plate with the same size.

Moderate problems of the finite FSS backed by dielectric substrate are solved with the SED basis function method. The original problem can be simplified to two smaller problems. It enables a significant reduction to the matrix size and storage, and efficient analysis of FSS can be performed. The band-stop type of FSS can be composed of periodic conductive patch cells on the dielectric substrate, and shows total reflection property at the resonant frequency.

The SED basis function method is mostly used to analyze periodic PEC structures in free space. The layered medium Green’s function is successfully employed and several dielectric substrate backed finite FSSs are discussed in this paper. The calculation of reflection and transmission coefficients, which are more effective rather than far field scattering of the FSS, are described.

Shape and material parameters have major influence on the performance of electromagnetic components. Optimization of these parameters is therefore vital in electromagnetic design. Reduction of the radar cross section (RCS) for aircraft and frequency selective surfaces are two well known examples. Shape and materials optimization is performed for different scatterers in 2D.

Continuum design sensitivities for microwave problems are applied for the gradient‐based optimization of scatterers' shape and material parameters. The goal function is chosen to be an average of the monostatic RCS for a sector of incident angles over a frequency band. Numerical tests are presented for 2D scatterers and, specifically, a perfectly electrically conducting scatterer and an absorber on the front edge of an airplane wing are considered. The results are compared with theoretical findings and results in the open literature.

It is demonstrated that a dense frequency sampling of the goal function over a wide frequency band relaxes the requirements on the angular resolution. The broad band requirements on the RCS also avoids corrugations without the resorting to regularization methods and penalty terms added to the goal function. The optimization algorithm refines, in a small number of iterations, the initial geometry of the scatterer to an optimized design with strongly reduced RCS.

Shape and material parameters have major influence on the performance of electromagnetic components. Optimization of these parameters for scatterers demonstrates that a densely evaluated goal function over a broad frequency band has the advantages of: lowering the requirements on angular resolution; avoiding corrugations; and regularizing the problem by the broad frequency band requirements which often are naturally included in the performance specification of electromagnetic devices.