Application of microwave holographic subsurface technology for non-destructive testing of reinforced polyurethane foam

Abstract

Glass fiber Reinforced Polyurethane Foam (RPUF) has found wide application primarily in the aerospace and construction industry due to its outstanding properties. Unlike pure non-reinforced Polyurethane Foam (PUF), it has increased strength characteristics and at the same time retains unique heat and sound insulation properties. The paper considers the features of reinforced polyurethane foam examination in the Microwave (MW) range. It is shown that there is a significant difference in the recorded MW images compared to pure polyurethane foam. This is expressed primarily in the fact that the reinforcing fibers have a dielectric constant that is different from enclosing polyurethane foam, which leads to scattering and reflection of the incident electromagnetic wave on them. Experimental studies have shown that for RPUF, in contrast to PUF, there is an optimal wavelength range in which the contrast of defects against the background of glass fiber reflections is of the greatest value. An experimental comparison of two methods of examination back-scattering and forward-scattering methods was also carried out for RPUF. It is shown that the forward-scattering technology of measurements, if it can be implemented, has certain advantages since allows reducing the contrast of background reflections from the reinforcing fibers.