Millimeter-Wave Tomographic Imaging of Composite Materials

Modern composite materials require measurement technologies, which can detect and classify critical defects during and after the manufacturing process. This thesis provides a theoretical and experimental investigation of the capabilities of millimeter-wave-based measurement systems for the above-mentioned task. It is demonstrated, that such systems are well suited as non-destructive and non-contact measurement tools for composite materials.

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To utilize the full potential of modern composite materials, new and innovative inspection methods are required to detect and classify defects, which are critical to the mechanical properties of the components. Ideally, such methods are non-contact, non-destructive, and can be applied during the manufacturing process, as well as during the complete lifespan of the components. Measurement systems based on millimeter waves meet these requirements, however, so far, such technologies are not used in an industrial environment, despite their potential of increasing the quality and efficiency of composite materials. Based on the propagation properties of millimeter waves, interacting with composite materials, the capabilities of such millimeter-wave-based measurement systems are investigated. Various measurement systems, operating at different frequency ranges within the millimeter wave spectrum, are developed to demonstrate the capabilities of such systems. This includes various signal-processing methods to provide an optimized evaluation of the measured signals, enabling high-resolution, non-destructive, and non-contact tomographic measurements with the presented measurement technology.