Microwave Tomography With LSTM-Based Processing of the Scattered Field

The quantitative inspection of unknown targets or bodies by means of microwave tomography requires a proper modeling of the field scattered by the structures under test, which in turn depends on several factors related to the adopted antennas and measurement configuration. In this article, a multifrequency tomographic approach in nonconstant-exponent Lebesgue spaces is enhanced by a preliminary step that processes the measured scattered field with a neural network based on long short-term memory cells. In the considered cases, this approach allows dealing with measurements in three-dimensional settings obtained with non-ideal antennas and measurement points, while retaining a canonical two-dimensional formulation of the inverse problem. The adopted data-driven model is trained with a set of simulations of cylindrical targets performed with a finite-difference time domain method, considering a simplified bistatic measurement configuration as an initial case study. The inversion procedure is then validated with numerical simulations involving cylindrical and spherical structures

A two-step multifrequency imaging technique for ground penetrating radar

In the present paper, a combined method for ground penetrating radar imaging is presented. The proposed technique has a first step in which the electric field scattered by the buried structure is estimated and a qualitative reconstruction is obtained, and a second quantitative inversion step for reconstructing the dielectric properties of the buried targets. The full-wave multifrequency inexact-Newton inversion approach used in the second step uses the information about the target position extracted by the qualitative procedure and takes the scattered field data estimated by a time-domain filtering method. Numerical simulations are presented to prove the effectiveness of the proposed technique

Electromagnetic biomedical imaging in Banach spaces: A numerical case study

This paper reports the results of the application of a microwave imaging method developed in Banach spaces to a model of human head in presence of a hemorrhagic brain stroke. The approach is based on the integral equations of the inverse scattering problem. A Gauss-Newton scheme is adopted as a solving procedure. Being developed in Banach spaces, the method turns out to be quite efficient in reducing the over-smoothing effects usually associated to Hilbert-space reconstructions. Numerical simulations are reported involving a realistic model of human head

Open-Source Software for Electromagnetic Scattering Simulation: The Case of Antenna Design

Electromagnetic scattering simulation is an extremely wide and interesting field, and its continuous evolution is associated with the development of computing resources. Undeniably, antenna design at all levels strongly relies on electromagnetic simulation software. However, despite the large number and the high quality of the available open-source simulation packages, most companies have no doubts about the choice of commercial program suites. At the same time, in the academic world, it is frequent to develop in-house simulation software, even from scratch and without proper knowledge of the existing possibilities. The rationale of the present paper is to review, from a practical viewpoint, the open-source software that can be useful in the antenna design process. To this end, an introductory overview of the usual design workflow is firstly presented. Subsequently, the strengths and weaknesses of open-source software compared to its commercial counterpart are analyzed. After that, the main open-source packages that are currently available online are briefly described. The last part of this paper is devoted to a preliminary numerical benchmark for the assessment of the capabilities and limitations of a subset of the presented open-source programs. The benchmark includes the calculation of some fundamental antenna parameters for four different typologies of radiating elements

An inverse scattering procedure in Lebesgue spaces with non-constant exponents

Within the ever-growing field of electromagnetic imaging, inversion procedures are conventionally described in the mathematical framework of Hilbert spaces. Usually, the over-smoothing effects and oscillations that arise using a Hilbert-space formulation make the dielectric reconstruction of targets inaccurate. This problem is strongly reduced by the recent development of inversion techniques in Banach spaces. However, the selection of the Banach space norm parameter is critical for obtaining precise reconstructions, and no exact rules exist for this choice. To overcome this issue, an innovative approach in variable exponent Lebesgue spaces is proposed here, along with a preliminary numerical validation

GPR imaging techniques for non-destructive inspection of concrete structures

open4noVol. 21, EGU2019-8897openRandazzo, Andrea; Fedeli, Alessandro; Pastorino, Matteo; Pajewski, LaraRandazzo, Andrea; Fedeli, Alessandro; Pastorino, Matteo; Pajewski, Lar

Microwave sensor network for quantitative characterization of targets: A proof-of-concept

The possible use of a microwave sensor network for quantitatively reconstructing the electromagnetic properties of unknown targets is considered in this paper. In particular, a set of microwave sensors is used to measure the z-component of the electric field in a free-space scenario. The resulting field measurements are then processed by means of an inversescattering based technique, which provides an estimated map of the dielectric properties of the targets eventually present in the area under investigation. Preliminary numerical results in a simulated environment are shown in order to initially assess the feasibility of the proposed approach

Microwave Imaging of 3D Dielectric Structures by Means of a Newton-CG Method in Spaces

An increasing number of practical applications of three-dimensional microwave imaging require accurate and efficient inversion techniques. In this context, a full-wave 3D inverse-scattering method, aimed at characterizing dielectric targets, is described in this paper. In particular, the inversion approach has a Newton-based structure, in which the internal linear solver is a conjugate gradient-like algorithm in lp spaces. The presented results, which include the inversion of both numerical and experimental scattered-field data obtained in the presence of homogeneous and inhomogeneous targets, validate the reconstruction capabilities of the proposed technique

Microwave imaging of mixed metallic–dielectric configurations via a finite element-based variable exponent approach

The quantitative reconstruction of structures that include both metallic and dielectric targets at the same time is addressed in this article. In particular, a nonlinear tomographic inversion approach developed in variable exponent Lebesgue spaces with a finite element (FE) formulation is adopted for the first time in such a configuration. Results obtained within a simulated environment are presented to validate the proposed technique and analyze the effects of different numbers and sizes of the metallic targets present in the investigated scenario. Moreover, the impact of possible a priori knowledge of metallic structures is assessed