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In many cryogenic systems, during useful life, defects or degradation of performance are found. Frequently these malfunctions are due to the presence of alterations in the characteristics of the thermal insulating materials used to coat the metal parts of the system. It is useful to evaluate methods for investigating the quality of insulating coatings by means of instruments, with low cost, that can be easily used during production. Thermal insulating materials are characterized by a relative dielectric constant close to the unit and a low Loss Factor: this work aims to investigate the use of microwave holographic radar for the detection of defects in such materials. The results show good detectability of defects when they are oriented as the antenna axis. Finally, it is shown that the robotic scan can examine large areas with the same detection performances of manual scan but with less set up and scanning time. [ABSTRACT FROM AUTHOR]

The evaluation of microwave (MW) imaging radar capabilities in non-destructive tests to detect internal structures or defects in the inner volume of thermal insulation coating has been carried out. The MW imaging with high spatial resolution has been performed with holographic subsurface radar operated in the frequency range from 22.2 to 26.2 GHz. The investigation of this non-destructive testing (NDT) technology is important to evaluate the feasibility for quality check of assembled polyurethane sandwich parts for thermal insulation. The samples of polyurethane foam thermal insulation have been fabricated in collaboration with a manufacturing industry of household appliances to have a representative set of real defects. The images obtained are of high quality and easy to be interpreted as they reveal the shapes and plane positions of the defect into samples with thickness up to 90 mm. • Microwave NDT of thermal insulating materials. • Microwave imaging with 22 GHz holographic subsurface radar. • Defects detection by high resolution imaging. • NDT investigation of polyurethane foam thermal insulation materials. • Detection and reconstruction of microwave holograms. [ABSTRACT FROM AUTHOR]