GPR data enhancement via multiple reflections' filtering

Based on a classification methodology for multiple reflections' (MR) identification recently published by the authors, this work proposes a filtering technique for GPR data to be integrated within the layer stripping (LS) approach. In LS, the reconstruction of the dielectric stack is obtained by recursively inverting the signals backscattered by each layer, from the top to the bottom. According to the state‐of‐the‐art, to simplify the solution of the problem, MR are commonly neglected. The scope of this article is therefore to first discuss the implementation of the MR filtering procedure within a LS algorithm and evaluate from the quantitative point of view which improvements this will yield to the overall performances. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Electromagnetic scattering by weakly lossy multilayer ellipticcylinders

The analytic solution to the electromagnetic scattering due to a multilayer elliptic cylinder is generalized to the case of weakly lossy materials by using a first-order truncation of the Taylor expansion of each Mathieu function     

Scattering by multilayer isorefractive elliptic cylinders

An analytical solution to the plane-wave electromagnetic scattering by multilayer elliptic cylinders is derived in the case of isorefractive materials. For these materials, a recursive solution similar to the solution for the multilayer circular cylinder is obtained. Moreover, it will be shown that the matrix-based recursive procedure for common dielectrics reduces to the present solution in this particular case. Finally, a number of numerical examples and comparisons will be provided.     

Equivalent current density reconstruction for microwave imagingpurposes

Numerical computer simulations are used to study the possibilities of reconstructing the distribution of the equivalent current density vector in a domain with a known volume, inside which dielectric scatterers stand at arbitrary locations. An integrodifferential formulation of the three-dimensional electromagnetic inverse scattering is transformed into matrix form through the application of the moment method. A pseudoinversion algorithm overcoming ill-conditioned problems is used to obtain the distribution of the equivalent current density also in the case where the input data (i.e. the simulated values of the scattered field vector to be obtained in an observation domain) are affected either by Gaussian noise or by uniformly distributed errors. The results furnish information that could be used to devise a possible imaging method for detecting the locations and surface shapes of scattering objects     

Reconstruction of dielectric permittivity distributions in arbitrary 2-D inhomogeneous biological bodies by a multiview microwave numerical method

A numerical method for microwave imaging of two-dimensional inhomogeneous biological bodies illuminated by TM waves is presented. It is a spatial-domain multiview approach which makes use of the moment method to discretize the integral-equation formulation of inverse scattering. A pseudoinversion technique is applied to obtain a minimum-norm solution for the equivalent current density inside the cross-section of a scatterer. A multi-illumination-angle multiview process is used. The invariance of the Green matrix makes it possible to perform only one pseudoinverse (off line and once for all), independently of the number of views, thus reducing the need for computer resources. A pixel representation is adopted, and a look-up table is utilized to fast synthesize images. No plane-wave illumination is required and no first-order approximations are applied. Distortions in the dielectric reconstruction and noise effects are evaluated via some numerical simulations.     

Extension of moment-method solutions to vector scattering by three-dimensional non-linear dielectric objects in free space

In this paper, we explore the possibility of applying the moment method to determine the electromagnetic field distributions inside three-dimensional bounded non-linear dielectric objects of arbitrary shapes. The moment method has usually been employed to solve linear scattering problems. We start with an integral equation formulation, and derive a non-linear system of algebraic equations that allows us to obtain an approximate solution for the harmonic vector components of the electric field. Preliminary results of some numerical simulations are reported.     

Electromagnetic imaging of penetrable configurations by means of a GA/CG method

The genetic algorithm is an important tool in image formation and processing. In the present paper, the genetic algorithm is used in conjunction with a conjugate gradient method as a tool for electromagnetic imaging of dielectric targets. The genetic algorithm is in principle able to reach the global minimum of the “fitness function” resulting from the fitting of the exact measured data with the field-scattered data corresponding to the parameters of the current “image” of the object under test. The conjugate gradient is used to enhance the convergence of the iterative method near the solution. In the following, the formulation of the new approach is described and a numerical assessment about robustness and effectiveness of the method is presented.     

Electromagnetic boundary value problem in the presence of a partlylossy dielectric: considerations about the uniqueness of the solution

This paper deals with the uniqueness of the solution of a boundary value problem defined by specifying the tangential components of the electric field over the closed regular boundary (or the tangential components of the magnetic field over the boundary, or the former components over part of the boundary and the latter components over the rest of the boundary) of a limited region containing a linear dielectric material not lossy everywhere. In particular, the uniqueness of the solution is proved in the case where the dielectric is everywhere linear, homogeneous, and lossless, except for a subregion where the dielectric is lossy, linear but not necessarily homogeneous     

Microwave imaging within the second-order Born approximation:stochastic optimization by a genetic algorithm

This paper addresses the problem of reconstructing the location, shape, and dielectric permittivity distribution of an inhomogeneous dielectric object from measurements of the field scattered by the object. The object is an inhomogeneous infinite cylinder of arbitrary cross section illuminated by a transverse magnetic incident electric field. The approach is based on the Lippmann-Schuringer integral equation for the electromagnetic inverse scattering problem, approximated by applying the second-order Born approximation, which allows an extension of the range of contrast values that can be accurately imaged. The numerical approach is developed in the spatial domain and makes use of a multi-illumination multiview processing. In particular, the inverse problem is recast in a global nonlinear optimization problem (including a penalty function), solved by a stochastic method based on a genetic algorithm. In this paper, the mathematical formulation of the approach is described and the results of several dielectric reconstructions are reported, including comparisons with analogous reconstructions performed within the linearized (first-order) Born approximation