Ricerc@Sapienza

In this paper, preliminary results of complex permittivity measurements of clay-brick material will be presented. The general aim of the experimental project is to correlate the measured permittivity of construction materials with the content of water and salt, in order to obtain information on the condition of ancient walls by using non-invasive techniques. The complex permittivity values reported in this paper have been obtained by waveguide measurements on samples of clay-brick dried and then immersed in demineralized water or in a saturated solution of demineralized water and NaCl.

This paper presents the validation and test of an experimental set-up for complex permittivity measurements of construction materials. Measurements on reference materials like Plexiglas® and PVC in an anechoic chamber and in a laboratory set up give results in agreement with literature data. The proposed set up is able to accommodate walls made with different construction materials and to measure their complex permittivity as a function of the frequency in the 2 - 6 GHz range.

A portable setup for measurements of complex permittivity based on ad-hoc arrangements is proposed and its performance compared to the ones of a bench system. The measurement setup consists of a portable spectrum analyzer (used as vector network analyzer, VNA) connected to an open-end coaxial cable for S-11 acquisition. Scattering parameters were processed using custom Labview software specifically developed to obtain complex permittivity of liquids and soft materials in real-time. A suitable calibration procedure, based on a differential principle, enables accurate measurements.