This study is focused on how to obtain the effective or equivalent properties of inhomogeneous materials, which, contrary to the usual metamaterials, are assumed to possess only a sandwichlike form of heterogeneity. More specifically, the aim is to see how the method of inversion, and associated type and amount of data, condition the outcome of the inversion, notably as concerns the possibility or not of exotic features such as simultaneous negative permittivity and permeability in certain frequency intervals. Two inversion schemes are considered and compared: the Nicolson-Ross-Weir (NRW) scheme and an optimization scheme. The adopted form of the optimization scheme provides only numerical retrievals, but it applies to any number of far-field data couples, which fact makes it a useful tool for determining whether the retrieved properties of an inhomogeneous material really are independent of the angle of incidence as is required for effective properties. It is shown, via the optimization scheme, that the apparently infinite number of solutions predicted by the NRW scheme is reduced to a single solution-closest to the predictions of a mixture model-when the constraint of independence with respect to angle of incidence is invoked. Moreover, this solution exhibits none of the exotic features of the properties of the usual metamaterials except temporal dispersion and loss even when the component materials of the inhomogeneous layer are neither dispersive nor lossy.
This paper presents an analytical calculation of magnetic field and electromagnetic performances of 3-, 5-, 7-, 9-, 11-phases cage rotor induction machines in healthy, broken bars and open phase's conditions. This model is formulated to consider all types of multi-phase/multipoles windings and used for the identification of electrical equivalent circuit (EEC) parameters. It's based on the subdomain model and the resolution of Poisson's, Laplace's, and Helmholtz's equations in each subdomain issued from Maxwell equations using the method of separation of variables and Fourier series when the machines are fed with sinusoidal current and voltage. The developed analytical model permits the calculation of magnetic field distribution, eddy current, circuit model parameters, and unbalanced magnetic radial force due to broken bars, electromagnetic torque and absorbed stator current. A comparative analysis between the studied five multi-phases machines is done with considering identical power rate. The analytical results are validated by those issued from the finite-element method (FEM).
We examine the effect of alignment errors on the performance of a frequency-diverse imaging system composed of metamaterial apertures. In a frequency-diverse imaging system, a sequence of distinct radiation patterns, indexed by frequency, provides measurements of the spatial content of a scene. This set of measurements can then be used to obtain a high-fidelity estimate of the scene using computational imaging techniques. As with any computational imaging system, realizing the full potential of the frequency-diverse system requires accurate characterization of the complex radiation patterns. This characterization entails precise knowledge of the locations and orientations of the transmitters and receivers; any discrepancy between the modeled and actual locations will introduce phase error and degrade the quality of image reconstructions. Here, we study the effect of various misalignment errors on the performance of a sparse, bistatic, frequency diverse imaging system and provide an estimate on the levels of error within which the frequency-diverse apertures can reconstruct high quality images. Depending on the misalignment type (i.e., displacement, rotation) and direction the phase error can change significantly. As a result, for instance, we show that the imaging system is significantly less sensitive to cross-range displacement errors than to range displacement errors. We also show that the displacement errors are reduced for larger systems comprising many sub-apertures, due to the reduced averaged phase error. We find the impact of rotational errors is small compared to that of the displacement errors. However, as the sub-aperture size increases, rotational errors become more pronounced, becoming severe for larger sub-apertures with multiple feeds.
Electrical cables of all types are subject to aggressive operational environments that can be source of defects or accelerated aging. Reflectometry-based methods are among the best ones for the detection and location of hard defects, but cannot easily provide efficient unambiguous diagnosis for complex topology networks, such as bus or star-shaped wired networks. This paper introduces the use of a new method, called transferometry, as an additional tool for the diagnosis of complex topology networks and shows that it presents many advantages compared to reflectometry, both in terms of implementation and data processing. Based on the fusion of the analysis results of several transmitted signals, it can provide a better diagnosis with fewer sensors than distributed reflectometry, with a simpler electronic architecture.
This paper investigates the cogging torque and torque ripple in high pole number interior permanent magnet generators, designed for direct-drive applications. Two interior permanent magnet rotor topologies --- flat-shaped and V-shaped were considered with distributed wound and fractional slot concentrated wound stators. A comparison of torque performances was made between distributed wound and fractional-slot concentrated wound generators. Cogging torque was minimized by finding an optimum magnet pole arc length and torque ripples were minimized by finding optimum slotopening and flux barrier shape. Design analysis was carried out in finite element models. It was found that flat-shaped rotor topology in the fractional slot concentrated wound stator can provide the best torque performance regarding low cogging torque and torque ripple. This finding was verified in constructed prototype machine.
In this paper, a new analytically regularizing method, based on Helmholtz decomposition and Galerkin method, for the analysis of the electromagnetic scattering by a hollow finite-length perfectly electrically conducting (PEC) circular cylinder is presented. After expanding the involved functions in cylindrical harmonics, the problem is formulated as an electric field integral equation (EFIE) in a suitable vector transform (VT) domain such that the VT of the surface curl-free and divergence-free contributions of the surface current density, adopted as new unknowns, are scalar functions. A fast convergent second-kind Fredholm infinite matrix-operator equation is obtained by means of Galerkin method with suitable expansion functions reconstructing the expected physical behaviour of the unknowns. Moreover, the elements of the scattering matrix are efficiently evaluated by means of analytical asymptotic acceleration technique.
In fixed-receiver bistatic synthetic aperture radar (SAR), the spaceborne SAR is used as an illuminator. The direct-path signal and bistatic SAR raw data are sampled by the fixed-receiver which is placed on the top of a building or a hill. As the direct-path signal has high signal-tonoise ratio (SNR) advantage and almost the same synchronization error terms, it is used as the reference signal for the range matched filtering. Then the range compression can be realized with a time and frequency synchronization process. However, after range match filtering by the directpath signal, the range history of point target consists of three square-root terms, for which it is hard to use the Principle of Stationary Phase (POSP). Meanwhile, the two-dimensional (2-D) spatial variation of the target's 2-D frequency spectrum is serious. By combining azimuth preprocessing, directpath signal compensation and nonlinear Chirp Scaling (NLCS) imaging algorithm, a new focusing algorithm is presented in this paper. Simulation results of point targets are presented to validate the efficiency and feasibility of the proposed imaging algorithm. Finally, this algorithm is also validated by the measured data which is obtained using the HITCHHIKER system.
Using the program of numerical simulation of ultrawideband pulse reflection from dielectric medium with random rough surface, a possibility to detect ideally conducting objects placed near the surface was investigated. Medium parameters corresponded to the cases of the dry and wet sandy ground. Based on the correlation analysis of the reflected objects with orthogonal polarizations, a decision about the presence or absence of an object was made. An ideally conducting rectangular object was buried into the ground with a random rough surface to different depth. A cross-shaped metal object was disposed above the surface.
We present a hierarchical layer-multiple-scattering method of electromagnetic waves for the study of photonic structures consisting of many-scatterers per unit cell (clusters of scatterers) where the scatterers are in general non-spherical and/or anisotropic or inhomogeneous. Our approach is a two-stage process where we take into account all the multiple-scattering events involved: (a) among the scatterers of the cluster comprising the unit cell of the structure, and (b) among the clusters within the structure. As text cases, we model the optical properties of plasmonic metamaterials made from clusters of gold nanocubes.
In this paper we present the full process of designing anisotropic metamaterial (MM) wide angle impedance matching (WAIM) layers. These layers are used to reduce the scan losses that occur in active phased arrays for large scanning angles. Numerical results are provided to show the improvement in performances that such layers can ensure. The proposed anisotropic MM-WAIM layers achieve an improvement of about 1 dB of more radiated power at θ = 70˚ from broadside, in a 13% of fractional bandwidth on the azimuthal plane Φ = 90˚. Weaker improvements are obtained in the other azimuthal planes, however keeping the active reflection coefficient below -9 dB for all azimuthal planes up to θ = 60˚ and up to θ = 70˚ off-axis for planes Φ = 45˚; 90˚ in the whole operational band.