The sub-terahertz (THz) frequency band has proved to be a noteworthy option for nondestructive testing (NDT) of nonmetal aeronautics materials. Composite structures or laminates can be inspected for foreign objects (water or debris), delaminations, debonds, etc., using sub-THz sensors during the manufacturing process or maintenance. Given the harmless radiation to the human body of this frequency band, no special security measures are needed for operation. Moreover, the frequency-modulated continuous-wave sensor used in this study offers a very light, compact, inexpensive, and high-performing solution. An automated two-dimensional scanner carrying three sensors partially covering the 70- to 320-GHz band is operated, using two complementary measurement approaches: conventional focused imaging, where focusing lenses are used; and synthetic aperture (SA) or unfocused wide-beam imaging, for which lenses are no longer needed. Conventional focused imagery offers finer spatial resolutions but imagery is depth-limited due to the beam waist effect, whereas SA measurements allow imaging of thicker samples with depth-independent but coarser spatial resolutions. The present work is a compendium of a much larger study and describes the key technical aspects of the proposed imaging techniques and reports on results obtained from human-made samples (A-sandwich, C-sandwich, solid laminates) which include diverse defects and damages typically encountered in aeronautics multilayered structures. We conclude with a grading of the achieved results in comparison with measurements performed by other NDT techniques on the same samples

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Recently, there has been a significant interest in employing high frequency radar imagery for many industrial oriented and security applications. The quality control of aeronautics composite multi-layered materials and structures through Non-Destructive Testing (NDT) is the main focus of this study. The main motivations for using this technology are: it allows penetration of most non-metal and non-polarized materials, it provides the ability for three-dimensional (3-D) imagery and in-depth information, and the millimeter waves (mmW) pose no health risk to the operator. The main goal of this research is to develop an integrated, semi-automatic and near real-time mode-operated image processing methodology for frequency-modulated continuous-wave (FMCW) millimeter wave images with center frequ encies around 100 GHz and 300 GHz. The proposed methodology firstly foresees to process reflectance and transmittance 3-D imagery by extracting areas of interest and object's boundaries at two operated frequencies. Then, the detected areas are subjected to a multi-source database and integrated by a decision tree algorithm. The fused information is used to identify defects and in-homogeneities within the objects. Finally, the post-processing phase examines and evaluates the spatial accuracy of the extracted information

The increasing industrial application of fiber reinforced plastics demands developments of new techniques for non-destructive testing. The sub-terahertz frequency band has proved to be a noteworthy option for this task. Composite structures or laminates can be inspected for foreign inclusions, delaminations, debonds, etc., using sub-terahertz sensors during the manufacturing process or maintenance. In this contribution we present our results using a frequency modulated continuous wave terahertz imaging system in comparison with conventional NDT measurements on several different GFRP samples. Thereby a semi-automatic terahertz image processing approach for enhanced defect detection is applied

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