Misure non invasive a microonde ed ultrasuoni su materiali lapidei

During a stage at ISTI's Signals and Images Laboratory, I performed a number of nondestructive near-field microwave tests on lapideous materials relevant to cultural and architectural heritage (different marble samples), to detect and identify possible internal anomalies. The final goal is to experiment resonant microwave sensors developed at ISTI and to validate pre-existing measurements on the same samples, also comparing the results with the typical permittivity values found in the literature. The technique considered uses a narrowband patch antenna whose resonant frequency depends on the material illuminated. By inverting the formula for the resonant frequency, the permittivity of the material under test, averaged over the illuminated volume, can be estimated, thus allowing a map of this quantity to be reconstructed as a function of the sensor position. The results obtained are presented and discussed. Complementary measurements based on ultrasound transmission were not performed because of a delay in a previously scheduled field measurement campaign.