Millimeter-Wave Tomographic Imaging of Composite Materials Based on Phase Evaluation

A novel data processing algorithm for the generation of tomographic images of composite materials, based on measurements acquired via frequency-modulated continuous-wave (FMCW) radars operating in the millimeter wave regime, is presented. The presented algorithm, in tandem with the applied method and achieved results, provides valuable information for the optimization of the quality and efficiency of composite-based components. By utilizing the high sensitivity of the signals' phase, the detection and classification of defect type, shape, and position are possible. Since the ambiguity of the phase generates radar images resembling optical fringe patterns, the data evaluation is inspired by the respective fringe pattern analysis, as often utilized in optics. The signal processing is adapted accordingly to match the radar-based data. To demonstrate the feasibility of the proposed algorithm, glass fiber reinforced plastic samples with deliberate and predefined defects, including resin wedges and dry fibers, are measured with a radar system operating in W-band (75-110 GHz), with the used bandwidth of 24 GHz and the signal focused to the sample under test.