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2003
Conference Paper
Titel
Contactless characterization of coatings with a microwave radar sensor
Abstract
Free field microwave methods are well suited to characterize dielectric materials both in nondestructive and in contactless way. Variations of the distance between test object and the microwave sensor (air gap) are influencing the measuring values as the air gap is part of the system under test. By additional and independent air gap measurement with a laser triangulation sensor or with air coupled ultrasound it is possible to correct the air gap variations. One potential application is the online surveillance of the plastics coating process of steel pipes. Measurements have been performed using a FMCW radar with a carrier frequency of about 94 GHz in reflexion mode and in combination with air gap mearurements. The accuracy of thickness measurement is about 0.05 mm or better. The characterization of thin metallic layers on dielectric substrate can be performed with quite inexpensive microwave sensors. While signal phase is the essential measuring quantity in monitoring of plastics coating, amplitude is essential in monitoring of thin metallic layers.