Determinazione dei parametri elettromegnetici di materiali compositi e loro variazioni in funzione del contenuto idrico e di inquinanti
Author(s)
Mattei, Elisabetta
Date Issued
October 8, 2008
Type
Doctoral Thesis
Abstract
This thesis is devoted to the electromagnetic techniques, the Time Domain Reflectometry (TDR) in particular, applied to the study of composite systems and to their possible employment in environmental sciences. The TDR, the LCR-meter, GPR (Ground Penetrating Radar) and conductimeter are the technique used in this study. The thesis develops as follows:
The TDR experimental device has been used to determine the geometric and electrical features of several probes via calibration measurements, carried out on materials with known electromagnetic properties (air and demineralized water). A new calibration method has been introduced (the derivatives method) and the comparison between this method and the others two used in literature (the tangents method and the transfer function method) demonstrated that the tangents method is affected by systematic errors when it is applied to a dispersive medium. So, the empirical curves used in literature to estimate the soil water content and obtained with the tangents method, should be re-calibrated using the new method.
Anhydrous mixtures of glass beads and magnetite have been analyzed in order to estimate the electromagnetic velocity and the attenuation factor. The measurements have been carried out on three grains size ranges for different magnetite volumetric contents. The data have shown that the electromagnetic wave propagation velocities decrease with the increase of the magnetite content and are independent on the grains sizes. For the bigger grains size range, the attenuation factor increases with the volumetric percentage of magnetite, while for the smaller one, the experimental uncertainties, probably due to filling problems, prevent the accurate determination of the attenuation factor. To determine the reliability of the TDR measurements, the attenuation values have been compared with those obtained by other techniques (LCR-meter and Network Analyzer).
Dispersion of olive waste waters has been studied by measuring the electrical conductivity by TDR. Some preliminary experiments have been realized to test the possibility of monitoring the propagation of the olive waste water. Three different media have been chosen to establish the influence of the solid matrix on the dispersion phenomena. The conductivity has been correlated to the volumetric content using calibration curves: the concentration versus time has been compared with the dispersion curves of specific theoretical models of literature and the propagation parameters have been estimated by the experimental data fitting.
TDR and GPR measurements have been carried out on a test-site. The test site consists of a pit filled with gravel and sand in which a pipe system for water inflow is buried. The data were collected under different water charge conditions and the water level was monitored by piezometers. TDR measurements were performed at various depths using a multilevel probe system and using vertical three wire probes. GPR measurements were performed with a system equipped with 250 MHz and 500 MHz antennas. The electromagnetic parameters obtained by TDR have been compared with the GPR data to find a correlation between water content provided by the two techniques.
Additional information
Dottorato di ricerca in Scienze ambientali
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