Samuel Poretti

A Microwave Tomographic System for Wood Characterization in the Forest Products Industry

Abstract Nondestructive testing and evaluation techniques able to extract information about the internal structure of the samples under test are very important in the wood industry. Microwave imaging systems have been considered for a long time promising apparatuses for this task. In this framework, approaches exploiting the full scattering phenomena for creating images of the distributions of the dielectric properties of the targets have been developed in the last few years. In this paper, a prototype of microwave tomographic system is presented and several experimental validation confirming its suitability for the use in the wood and forest product industry are reported.

Microwave imaging of foreign bodies inside wood trunks

The detection of foreign bodies inside wood trunks is a key task in the wood processing industry. Bullets, screws, or other debris can severely damage carpentry machinery, and, consequently, must be removed prior to processing. In this paper, the feasibility of a new prototype of microwave tomograph for the detection of metallic inclusions inside wood trunks is analyzed. Numerical simulations show that the proposed system configuration is able to acquire data that can be successfully used, in conjunction with a proper inversion procedure, to obtain the distribution of the conductivity of the sample under test, and consequently, to identify the presence of metallic inclusions.

Preliminary test of a prototype of microwave axial tomograph for medical applications

An existing prototype of microwave imaging tomograph, previously designed by the present Authors for non destructive testing (NDT) applications, has been adapted in order to deal with biomedical targets. The developed system allows collecting multi-view multi-frequency data. An efficient inversion procedure is used to retrieve the distributions of the dielectric properties from the measured field samples. Some numerical simulations aimed at validating the proposed system and preliminary measurement results obtained by using a breast phantom are presented in this paper.

Design of a slim wideband-antenna to overcome the strong reflection of the air-to-sample interface in microwave imaging

A new wideband sensor for microwave imaging is introduced. The structure consists of a folded quasi-self complementary monopole antenna which is applied in contact with the sample-under-test (SUT) to minimize the interface impedance mismatch. The sensor presents a slim design that allows the development of very compact antenna arrays, thus avoiding the need of coupling mediums.

Nondestructive Evaluations by Using a Prototype of a Microwave Tomograph

Microwave Materials Characterization is an edited book discussing recent researches on basic and innovative measurement techniques for the characterization of materials at microwave frequencies, in terms of quantitative determination of their electromagnetic parameters, namely the complex permittivity and permeability. It is divided into two parts: Part 1, including original contributions on advanced techniques for the characterization of dielectric materials, and Part 2, devoted to the microwave characterization of biological tissues.

In Situ Determination of Void Ratio and Compactness in Saturated Soils Using a Partially Automated Measuring System Based on Microwaves

Void ratio and compactness are two of the principal parameters used for the geotechnical characterization of soils. Amongst others, they determine the deformation, settlement or liquefaction potential, which in turn might significantly impair the quality as well as the performance of any soil foundation. Direct measurement of the natural void ratio, i.e. the parameter typically used as indication for the soil compactness, is particularly difficult since it requires undisturbed samples. Because of the difficulty to obtain such samples in their undisturbed state, indirect methods such as: SPT, NSPT or CPT, to mention only the most commonly used ones, have been developed and are widely used. However, such indirect methods have their limitations and often fail, especially with heterogeneous soils also containing coarser materials. Additionally, results interpretation is done by indirect, empirical correlations, and is often affected by uncertainty. This situation gave rise to develop a more reliable and flexible approach, allowing a direct quantitative measure of the in situ void ratio of saturated soils. In this article a newly developed, partially automated, measuring system based on microwaves, is presented. The measurement method and an application example will be illustrated.

Experimental analysis of dielectric structures with a two-step electromagnetic imaging method

A novel two-step electromagnetic imaging method, suitable for the analysis of hidden inclusions in dielectric structures, is reported in this paper. In particular, two distinct steps compose the present technique. The first one extracts from the raw data an estimation of the scattered field due to the inclusions, and provides a first qualitative reconstruction of the structure under test. This information is then exploited by the second step, in which a quantitative inexact-Newton inversion approach retrieves a map of the dielectric characteristics of the examined region. Experimental data obtained with a tomograph prototype are used to validate the proposed inversion scheme.

Imaging of dielectric targets with metallic inclusions by means of a prototype of microwave axial tomograph

Microwave systems are becoming powerful tools for imaging applications. In fact, when designed by taking into account the full scattering phenomena, they are able to directly provide information about the physical properties of the target under test. In this paper, the possibility of detecting metallic inclusions inside dielectric objects is assessed by using a prototype of a microwave axial tomograph, which is able to create images of the dielectric permittivity and of the electric conductivity of the inspected target.