Davide Franceschini

Three-Dimensional Microwave Imaging Problems Solved Through an Efficient Multiscaling Particle Swarm Optimization

An enhanced multistep strategy based on a multiresolution particle swarm optimizer is proposed for 3-D microwave imaging. The aim of such an integration is to improve the convergence capabilities of the approach and to reduce the dimension of the search space and the computational burden of the optimization strategy, thanks to a constrained control of the particle velocities adaptively determined. This favors the exploitation of the global search capabilities of the particle swarms also in the framework of large-scale 3-D inverse scattering problems. The proposed technique is assessed by considering numerical tests concerned with single and multiple 3-D targets. The results of an experimental testing are also discussed.

PSO-Based Real-Time Control of Planar Uniform Circular Arrays

This letter is aimed at assessing the effectiveness of the phase-only control strategy based on a customized PSO when applied to planar uniform circular arrays (PUCA) and in the presence of interferences both in the near-field and far-field of the antenna. The employed geometry seems to be suitable for a reliable and effective implementation of adaptive arrays in mobile devices thanks to its symmetry and geometric simplicity. For validation purposes, the proposed architecture is evaluated in the presence of a complex time-varying scenario both in terms of synthesized beam patterns and signal-to-interference-plus-noise ratio

Parallel GA-based approach for microwave imaging applications

Genetic algorithms (GAs) are well-known optimization strategies able to deal with nonlinear functions as those arising in inverse scattering problems. However, they are computationally expensive, thus offering poor performances in terms of general efficiency when compared with inversion techniques based on deterministic optimization methods. In this paper, a parallel implementation of an inverse scattering procedure based on a suitable hybrid genetic algorithm is presented. The proposed strategy is aimed at reducing the overall clock time in order to make the approach competitive with gradient-based methods in terms of runtime, but preserving the capabilities of escaping from local minima. This result is achieved by exploiting the natural parallelism of evolutionary techniques and the searching capabilities of the hybrid approach . The effectiveness of the proposed implementation is demonstrated by considering a selected numerical benchmark related to two-dimensional scattering geometries.

A versatile enhanced genetic algorithm for planar array design

In order to synthesize planar, sparse, and aperiodic arrays, a numerical procedure based on an enhanced genetic algorithm is proposed. The method maximizes a suitably defined singleobjective fitness function iteratively acting on the states and the weights of the elements of the array. Such a cost function is related to the shape of the desired beam pattern, to the number of active elements and to others user-defined array-pattern constraints. To preliminarily assess the effectiveness of the approach, selected numerical experiments are performed. The obtained results seem to confirm its feasibility. Moreover, given the heterogeneity of the test benchmarks, the versatility is pointed out as a key-feature of the implemented methodology.

Full-vectorial three-dimensional microwave imaging through the iterative multiscaling strategy-a preliminary assessment

In this letter, a multiscaling strategy for full-vectorial three-dimensional inverse scattering problems is presented. The approach is fully iterative, and it avoids solving any forward problem at each step. Thanks to the adaptive multiresolution model, which offers considerable flexibility for the inclusion of the a priori knowledge and of the knowledge acquired during the iterative steps of the multiscaling process, the overall computational burden as well as the dimension of the search-space is considerably reduced. This allows to balance effectively the tradeoff between computational costs and achievable resolution accuracy. The effectiveness of the proposed approach is demonstrated through a selected set of preliminary experiments using homogeneous dielectric scatterers in a noisy synthetic environment.

Iterative image reconstruction of two-dimensional scatterers illuminated by TE waves

The iterative reconstruction of unknown objects from TE-measured scattered field data is presented. The paper investigates the performance of the iterative multiscaling approach (IMSA) in exploiting transverse electric (TE) illuminations. As a matter of fact, in these conditions, the problem turns out to be more complicated than the tranverse magnetic (TM) scalar one in terms of mathematical model as well as computational costs. However, it is expected that more information on the scenario under test can be drawn from scattered data. Therefore, this study is aimed at verifying whether the TE case can provide additional information on the scenario under test (compared to the TM illumination) and how such an enhancement can be suitably exploited by the IMSA for improving the reconstruction accuracy of the retrieval process. Such an analysis will be carried out by means of a set of numerical experiments concerned with dielectric and metallic targets in single- and multiple-objects configurations. Synthetic as well as experimental data will be dealt with.

Multi-Resolution Iterative Inversion of Real Inhomogeneous Targets

This paper presents a review of the reconstruction results obtained from the inversion of experimental data provided by the Institute Fresnel in Marseille (France) and concerned with inhomogeneous dielectric tergets and hybrid configurations, where dielectric and metallic cylinders are present in the scenario under test.

Dealing With Multifrequency Scattering Data Through the IMSA

A set of representative results are presented that are obtained with two multiresolution strategies developed for dealing with multifrequency inverse scattering experiments starting from the iterative multiscaling approach previously studied for monochromatic illuminations. The first approach is concerned with the integration of the iterative multiscaling algorithm into a frequency-hopping reconstruction scheme, while the second one allows a multiresolution simultaneous processing of multifrequency data. The numerical and the experimental analysis are aimed at assessing both the reconstruction effectiveness and the required computational costs of the two- and three-dimensional implementations of the proposed inversion schemes in comparison with the monochromatic multistep process and to the single-step optimization strategy, as well.

Assessment of the reliability and exploitation of the information content of inverse scattering data through a fuzzy-logic-based strategy - preliminary results

The presence of noise in measured data should be carefully considered in inverse scattering methodologies, because of the intrinsic ill-conditioning of the problem. To limit the effects of noise on the retrieval procedure, this letter presents an innovative fuzzy-logic-based approach. The proposed strategy allows one to take into account the corrupted nature of the data by fully exploiting all the available information content of the measurements. Selected synthetic and experimental test cases are considered for assessing the effectiveness of the proposed approach also in comparison with a reference inverse scattering technique.

Microwave Imaging from Amplitude-Only Data - Advantages and Open Problems of a Two-Step Multi-Resolution Strategy

In this report, a two step strategy for the inversion of amplitude-only data in microwave imaging applications is analyzed. At the first step of the proposed method, the illuminating source is synthesized according to a line sources model in order to compute the incident field in the investigation domain starting from the values available in the measurement domain. The second step is aimed at reconstructing the profile of the objects under test thanks to the iterative multi-scaling approach integrated with the Particle Swarm Optimizer, an effective evolutionary minimization technique. The reconstruction accuracy of the proposed phaseless retrieval strategy is analyzed using synthetic data concerned with a multiple scatterer configuration and successively further assessed inverting experimental data