Showing papers by "Giuseppe Vecchi published in 2015"

On the Numerical Simulation of Metasurfaces With Impedance Boundary Condition Integral Equations

Abstract: Metasurfaces are thin metamaterial layers characterized by unusual dispersion properties of surface/guided wave and/or reflection properties of otherwise incident plane waves. At the scales intervening in their design, metasurfaces can be described through a surface impedance boundary condition. The impedance, possibly tensorial, is often “modulated,” i.e., it can vary from place to place on the surface (by design). We investigate on different integral equation formulations of the problem, with special attention to the stability properties of the resulting system matrix.

A Nonconformal Domain Decomposition Scheme for the Analysis of Multiscale Structures

Abstract: We present a domain decomposition (DD) framework for the analysis of impenetrable structures; it allows for the electric field integral equation (EFIE) and combined field integral equation (CFIE), and for open, closed, and open–closed structures. The DD results in an effective preconditioner for large and complex problems exploiting iterative solution and fast factorizations. The DD employs specialized transmission conditions among the domains, and the use of discontinuous Galerkin (DG) allows conformal as well as nonconformal discretizations of domain boundaries; the nonconformal nature of the decomposition gives considerable flexibility in the meshing. The strategy is highly parallelizable, as all the operations involving the subdomains can be performed in parallel. The proposed scheme is implementation independent and can be easily merged with existing electromagnetic codes.

Wideband Fast Kernel-Independent Modeling of Large Multiscale Structures Via Nested Equivalent Source Approximation

Abstract: We propose a wideband fast kernel-independent modeling of large multiscale structures; we employ a nested equivalent source approximation (NESA) to compress the dense system matrix. The NESA was introduced by these authors for low and moderate frequency problems (smaller than a few wavelengths); here, we introduce a high-frequency NESA algorithm, and propose a hybrid version with extreme wideband properties. The equivalent sources of the wideband NESA (WNESA) are obtained by an inverse-source process, enforcing equivalence of radiated fields on suitably defined testing surfaces. In the low-frequency region, the NESA is used unmodified, with a complexity of $\mathcal{O}(N)$ . In the high-frequency region, in order to obtain a fixed rank matrix compression, we hierarchically divide the far coupling space into pyramids with angles related to the peer coupling group size, and the NESA testing surfaces are defined as the boundaries of the pyramids. This results in a directional nested low-rank (fixed rank) approximation with $\mathcal{O}(N\log{N})$ computational complexity that is kernel independent; overall, the approach yields wideband fast solver for the modeling of large structures that inherits the efficiency and accuracy of low-frequency NESA for multiscale problems. Numerical results and discussions demonstrate the validity of the proposed work.

Antenna placement based on accurate measured source representation and numerical tools

Abstract: Accurate electromagnetic models of measured antennas are available from the expansion of the measured field using equivalent currents [1–4]. The constructed model is importable in commercial Computational Electromagnetic (CEM) solvers in the form of a Huygens Box [5–9]. In flushmounted antenna applications, the measurement of the antenna sited in a locally relevant scenario and subsequent data processing require special attention. This paper, discuss details of the appropriate characterization of the source antenna for numerical computation in flush mounted scenarios. Post processing features and successive link to commercial CEM solvers are covered. The achieved accuracy of the measured source representation is investigated by comparing to full wave simulation.

Design and modeling of a microwave imaging system for breast cancer detection

Abstract: The main focus of the present paper is the design and construction of a microwave-imaging system prototype for use in research towards early breast cancer detection. To design and optimize the proposed system prototype, in particular to model the wideband antenna that acts as transmitter/receiver, a finite element method (FEM) approach is used. For signals generation and acquisition, low-cost yet high-precision off-the-shelf components replace a costly vector network analyzer (VNA). Even though the prototype is still under development, the agreement between simulations and measurements, the comparison with a reference VNA, and the validation with a commercial solver (FEKO) are encouraging.

Reconfigurable antenna system for wireless applications

Abstract: Nowadays wireless applications are widespread, and the demand for smart antenna technology grows exponentially. Although there are a large variety of effective algorithms to control antennas, they lack in the requirements of the next generation smart devices for industrial and societal applications which demand integration in compact, low cost and low power architectures. In this work we present a Wi-Fi device coupled with an antenna, where the receiver is able to adapt to a changing signal environment by providing a constant and reliable connectivity. Design criterion follows a strong low power approach, single front-end USB powered connected to an embedded low energy consumption platform. In addition, we come up in a low cost solution that does not require any external hardware. Decoding and antenna control algorithm are software-defined, while antenna beam steering is obtained by means of varactor diodes, voltage biased, used in a suitable way through hybrid couplers in phase shift configuration.

Hierarchical bases preconditioner to enhance convergence of the CFIE with multiscale meshes

Abstract: A hierarchical quasi-Helmholtz decomposition, originally developed to address the low-frequency and dense-discretization breakdowns for the EFIE, is applied together with an algebraic preconditioner to improve the convergence of the CFIE in multiscale problems. The effectiveness of the proposed method is studied first on some simple examples; next, test on real-life cases up to several hundreds wavelengths show its good performance.

Fast analysis of electrically large plasmonic arrays with aperiodic spiral order

Abstract: This work presents a fast analysis of electromagnetic scattering from arrays of metallic nano-particles with aperiodic spiral order The reported method extends the integral equation fast Fourier transform (IE-FFT) algorithm to the method of moments solution of PMCHWT integral equation for aperiodic homogenous dielectric arrays The algorithm relies on the interpolation of Greens function by Lagrangian polynomials on a uniform Cartesian grid Hence, the matrix-vector product in the iterative solver can be computed via the fast Fourier transform The memory requirement and the computational complexity of the algorithm tend to stay close to O(N) and O(NlogN), respectively, where N is the number of unknowns Some numerical examples are included, which illustrate the accuracy and capability of the present method

Automatic h-refinement through a-posteriori error estimation and discontinous Galerkin

Abstract: This work describes an automatic tool able to estimate the error in the Integral Equation solution in order to refine the mesh where the error is higher than the chosen threshold. The local refinement is performed through a hierarchical dyadic subdivision on the selected triangles to reach the desired error. As the resulting mesh is non-conformal, a Discontinous Galerkin scheme is applied.

Advanced cross polar source diagnostics based on the equivalent currents reconstruction from measured data

Abstract: The equivalent current (EQC) technique applied on antenna measurements has been demonstrated to be an efficient tool for diagnostics in many measurement situations [15]. Indeed the equivalent currents can be applied in tasks such as the filtering of disturbances such as undesired coupling with the supporting structure or the feeding and in NF-NF transformation. In particular the filtering capabilities have been efficiently demonstrated for suppressing the disturbances due to the presence of the feeding cable and of the mounting support in the measurement set-up in a sleeve dipole and a TT&C antenna [6]. The study was focused on the analysis of the co-polar component of the radiated field. Starting from the past results [6] we present in this paper a new study of the TT&C antenna extended also to the diagnostic of the cross-polar antenna sources.

Parametric interpolation using physics-based basis functions

Abstract: An interpolation procedure to approximate the electromagnetic responses of structures for different values of some parameters describing the structures geometry is presented. Basis functions are obtained from known families (e.g. polynomials or trigonometric polynomials) and from a post-process of some actual responses of the system. The fitting, in the least squares sense, can be handled efficiently leveraging on the Kronecker form of the resulting linear system.

Empirical study of a Reduced Order Model for electromagnetic scattering problems

Abstract: Some numerical results about the use of a Reduced Order Model to map currents to their radiated field in the presence of a scatterer are shown for antenna design and placement.

Frequency interpolation in the method of moments using the Discrete Empirical Interpolation Method

Abstract: We present some preliminary results on the construction of a Reduced Order Model to simulate the electromagnetic response of a structure at different frequencies with Surface Integral Equations. The Discrete Empirical Interpolation Method, introduced for the simulation of nonlinear differential equations, is used in this context to accelerate the construction of the Reduced Order Model.

Correlation Between Radiologic and Functional Status

Abstract: Background: High-resolution CT (HRCT) scanning plays an important role in the diagnosis of diffuse cystic lung diseases (DCLDs). However, its role in the clinical evaluation of patients affected by DCLD has not yet been well-clarified. At present, pulmonary function tests are the only methods available for the evaluation of lung impairment due to these diseases, but their sensitivity and reliability are still limited. Purpose: The aim of this study was to correlate the quantitative score of cystic-aerial lesions obtained by a HRCT density mask (DM) software with pulmonary function data in DCLDs. Methods: Spirometry, lung volumes, diffusion capacity, arterial blood gas (ABG) analysis, 6-min walking test (6-MWT), and HRCT with DM quantitative evaluation were performed in a cohort of 25 patients (lymphangioleiomyomatosis [LAM], 13 patients; Langerhans cells histiocytosis [LCH], 12 patients). Linear regression was used for the statistical analysis. The sum and mean of the air-trapping percentages at three different levels of DM study (ie, aortic arch, left lower lobe bronchus origin, and 2 cm from the diaphragmatic muscle), and various functional parameters and exercise performance values were matched for the analysis. Results: An obstructive pattern was present in 13 patients (52%; LCH group, 8 patients; LAM group, 5 patients). A predominant restrictive pattern was detected only in three patients (12%; LCH group, two patients; LAM group, one patient). Nine patients (36%) walked 4 U). The results of DM quantitative study (sum and mean) significantly correlated with FVC (r 0.56; p < 0.001), FEV1/vital capacity (r 0.94; p < 0.002), midexpiratory phase of forced expiratory flow (r 0.84; p < 0.05), FEV1 (r 0.82; p < 0.05), and diffusing capacity of the lung for carbon monoxide (r 0.82; p < 0.05), bronchial airway resistance (r 0.79; p < 0.05), and distance walked on the 6-MWT (r 0.53; p < 0.05). No significant correlation was found with the results of ABG analysis. Conclusions: In DCLDs, HRCT scans with quantitative assessment performed by a DM software showed a very good correlation with functional parameters. Therefore, DM could be considered, in combination with a complete functional assessment, in the initial evaluation of patients affected by DCLDs. However, further studies are needed to assess its usefulness in the follow-up of these patients. (CHEST 2004; 125:135–142)

Design and breadboarding of a frequency-reconfigurable, board-mounted compact antenna

Abstract: A quad-band patch antenna, fully integrated on a Printed Circuit Board, has been designed by means of an evolutionary method which merges Genetic Algorithm and frequency reconfigurability; the latter is implemented through a set of switches connecting the antenna patch to the ground plane. A prototype of the output device (antenna and Printed Circuit Board) has been built and its performance has been tested and compared with the numerical results: the agreement between simulations and measurements is satisfactory.

A kernel-independent wideband nested equivalent source approximation

Abstract: We introduce a kernel-independent wideband nested equivalent source approximation method. The nested equivalent source approximation (NESA), proposed by these authors to solve low frequency problems with linear complexity, is extended here to electrically large multiscale structures. The low frequency algorithm is directly employed at the bottom levels of an Octree clustering; in the high frequency regime, the directional low rank property is exploited, yielding a nested directional algorithm (Wideband NESA-WNESA) with O(N log N) complexity. Numerical results demonstrate the validity of the proposed solver.

A domain decomposition framework for the solution of multi-scale problems using integral equation formulations

Abstract: A general framework for the analysis of perfect electric conductor structures is presented; the proposed strategy is based in the decomposition of single structure into non-connected domains, whose individual analysis are used as preconditioner, obtaining good convergence properties for the iterative solution of the entire structure. Transmission conditions between the sub-domains are imposed using discontinuous Galerkin, and then are enhanced by enlarging the sub-domains information.

Domain decomposition for integral equation formulations for the analysis of complex open/closed structures

Abstract: This paper presents a new domain decomposition scheme for the analysis of structures in the Method of Moments context. The method is flexible in the sense that it allows the decomposition of complex structures according to the user needs, admitting tearing apart the structure into closed, open or closed-open portions (e.g. subdomains) without any limitation. Moreover, the use of Discontinuous Galerkin to enforce transmission conditions among the subdomains, permits both conformal/Non-conformal discretizations, decreasing in great manner the mesher burden, as for each subdomain can be discretized independently.