A multiview microwave imaging system for two-dimensional penetrableobjects

A microwave imaging system is based on a multiview numerical solution to the integral equation of 2D transverse magnetic (TM) scattering is proposed. This solution is achieved by the moment method, and a pseudoinversion transformation is used to face ill-conditioning problems. All experimental setup is described that uses a scanning subsystem for measuring the values of the scattered electric field inside an observation domain located outside the investigation one (i.e., the area containing the cross sections of cylindrical dielectric scatters). Rotations of the investigation domain with respect to the scanning subsystem and the transmitting antenna allow a multiview imaging process. The imaging system does not require plane-wave illumination and does not use any first-order approximations; hence, it may be used even in the case of strong scatterers. The offline and once-and-for-all computation of the pseudoinverse matrix allows an inexpensive reconstruction in terms of computer resources. Some tests of the system were carried out, and the results are reported     

Two-dimensional microwave imaging approach based on a geneticalgorithm

A multi-illumination multiview approach to microwave imaging is proposed, which is based on a genetic algorithm (GA). The inverse problem is recast in an optimization problem, solved in the framework of the Born approximation. The formulation of the approach is described and images of reconstructed circular (multilayer) cylinders are reported     

Microwave imaging based on a Markov random field model

A new approach to microwave imaging of 2D inhomogeneous dielectric scatterers is presented. The method is developed in the space domain, and Markov random fields are used to obtain a model of the distributions of dielectric features in the scattering region. In this way, a-priori knowledge can be easily inserted in the imaging scheme. This stochastic approach gives rise to a functional equation that can be minimized by using a simulated annealing algorithm. An iterative scheme is derived that allows one to bypass the need for storing large matrices in the computer. Numerical simulation results, confirming the capabilities and effectiveness of the proposed method, are reported. Solutions have generally been obtained in few steps, and seem better than those obtained by other imaging techniques in the space domain. The capability of the algorithm to operate in a strongly noisy environment is also proved     

A reconstruction procedure for microwave nondestructive evaluation based on a numerically computed Green's function

This paper describes a new microwave diagnostic tool for nondestructive evaluation. The approach, developed in the spatial domain, is based on the numerical computation of the inhomogeneous Green's function in order to fully exploit all the available a priori information of the domain under test. The heavy reduction of the computational complexity of the proposed procedure (with respect to standard procedures based on the free-space Green's function) is also achieved by means of a customized hybrid-coded genetic algorithm. In order to assess the effectiveness of the method, the results of several simulations are presented and discussed.     

Two-dimensional microwave imaging by a numerical inverse scatteringsolution

A numerical approach that aims to detect, by means of interrogating microwaves, the locations and the dielectric permittivities of unknown inhomogeneous dielectric cylindrical objects of arbitrary cross sections that might be present inside a fixed area of interest is proposed. An illumination is assumed with the electric field vector polarized along the cylindrical axis. The two-dimensional Lippman-Schwinger integral equation of electromagnetic scattering is transformed into matrix form by the moment method. The system obtained is solved by using a pseudoinversion algorithm to overcome ill-conditioning problems. The first-order Born approximation is also applied when the dielectric inhomogeneities are weakly scattering. Computer simulations have been performed by means of a numerical program. Results show the capabilities and limitations of the proposed approach     

Reconstruction algorithms for electromagnetic imaging

Two algorithms for image reconstruction in electromagnetic imaging are proposed. The first approach concerns the application of a hybrid version of the genetic algorithm to tomographic imaging of dielectric configurations. In the second approach, buried inhomogeneities are schematized as multilayer infinite dielectric cylinders with elliptic cross sections. An efficient recursive analytical procedure is used for the forward scattering computation. A cost function is constructed in which the field is expressed in series solution of Mathieu functions. Starting by the input scattered data, the iterative minimization of the functional is performed by a new optimization method called memetic algorithm.     

Microwave detection and dielectric characterization of cylindrical objects from amplitude-only data by means of neural networks

In this paper, we propose a new microwave technique for the localization and the dielectric characterization of physically inaccessible cylindrical objects from amplitude-only data. By means of a neural network used to solve the inverse scattering problem; this technique allows to directly achieve the object retrieval, avoiding the drawbacks related to the measurement of the phase distribution of the field that generally represent a critical point, especially at high frequency. The efficiency of the proposed technique in the reconstruction of both the position and the dielectric properties of a circular cylindrical body from amplitude-only information is illustrated and compared with the reconstruction performances of a neural network imaging technique that makes use of both amplitude and phase of the scattered field. The presence of noisy data is also taken into account, showing the dependence of the reconstruction accuracy on the signal-to-noise-ratio.     

Electromagnetic scattering by a multilayer elliptic cylinder undertransverse-magnetic illumination: series solution in terms of Mathieufunctions

An exact solution to the electromagnetic scattering by a dielectric multilayer infinite cylinder of elliptic cross section is proposed. The interfaces between different media, which are assumed to be lossless and nonmagnetic, are confocal elliptic cylinders. Starting from the series expansions in terms of Mathieu functions, an efficient recursive procedure for the computation of fields and radar cross sections per unit length under a transverse-magnetic illumination is developed. The mathematical formulation is detailed and some numerical results are provided     

Planar antenna array control with genetic algorithms and adaptive array theory

Planar arrays are successfully employed in radar and communication systems in order to allow three-dimensional-scanning. In the framework of real-time control of antenna arrays, starting from the Applebaum theory, this paper presents an approach based on a customized genetic algorithm aimed at adaptively eliminating interfering signals. Successful applications are presented in order to evaluate the effectiveness of the proposed approach in term of performances and computational complexity.     

An electromagnetic imaging approach using a multi-illuminationtechnique

An approach to microwave imaging using a multi-illumination technique is proposed. The numerical solution is reached by a multi-illumination-angle multiview approach based on the moment method. The aim is to extend the application range of the Born approximation by utilizing a-priori information about a scatterer. The basic idea of the approach is outlined, and preliminary results are reported