Nondestructive and contactless materials characterization with the help of microwave sensors

With the help of microwave sensors it is possible to characterize nonconductive test objects in nondestructive and contactless manner concerning the materials properties like the permittivity and the correlated materials parameters like density or porosity. Since the specimen geometry influences the measuring quantities the specimen dimensions like thickness can be determined, too, if the materials properties remain constant. In the frame of experimental investigations the density of foam specimens made of polyurethane could be determined with phase sensitive microwave sensors working at the frequencies of 2.45 GHz and 5.8 GHz. By applying a pattern recognition procedure this is possible even if the distance between sensor and test object is changing. With a monolithic frequency modulated continuous wave (FMCW) radar sensor working in the millimetre wave range (94 GHz) the thickness of the anticorrosive plastics layer (polyethylene) on a steel pipeline is measured contactlessly. By combining the millimetre-wave sensor with a distance sensor the unavoidable distance variation between sensor and pipeline occurring during coating process can be measured and corrected.