Microwave reflectometric methodologies for water content estimation in stone-made Cultural Heritage materials

In this work, the assessment of water content of building materials, to be used for moisture content monitoring of Cultural Heritage structures is addressed. To this purpose, different methods and probes were comparatively used to infer, noninvasively, the relationship between the water content of stone materials and the reflection properties at microwave frequency of the material. In particular, three types of probes were used: an open-ended coaxial probe; a patch resonator; and an open-ended waveguide. In addition, two different measurement instruments were compared; namely, a vector network analyzer and a time-domain reflectometer. Experimental tests were carried out on two types of stone materials (gentile and leccese stone), which are typically found in Cultural Heritage structures of Southern Italy. For each of the considered measurement systems, the experimental results and the related uncertainty evaluation are reported.