An Overview of Clutter Mitigation Methods for Tomographic Material Inspection

• Published in: IEEE transactions on microwave theory and techniques Vol. 69; no. 1; pp. 846 - 860
• Main Authors: Meier, Dominik, Gashi, Bersant, Zech, Christian, Baumann, Benjamin, Link, Torsten, Schlechtweg, Michael, Kuhn, Jutta, Rosch, Markus, Reindl, Leonhard M.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.01.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Clutter; Clutter mitigation; Composite materials; Glass fiber reinforced plastics; Inspection; Measurement methods; Millimeter waves; millimeter-wave radar; Nondestructive testing; Radar; radar clutter; Radar imaging; Signal processing; Signal resolution; Singular value decomposition; singular value decomposition (SVD); Spatial filtering; Three dimensional composites; Tomography
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2020.3034364

Millimeter wave-based material inspection methods are capable of providing 3-D-tomographic images of composite materials with a sufficient resolution to detect, localize, and classify critical defects. The nondestructive and noncontact-based measurement methods' potential can only be utilized with a complete understanding of the signals propagation behavior. Such that the relevant signal processing is tailored to the respective application. A core challenge of these systems remains clutter mitigation. Due to the composite materials' structure, a significant component of the received signal is corrupted by internal reflections, manifesting as clutter. For this purpose, a variety of different clutter mitigation methods, which include: normalization, moving average and moving median filter, entropy-based filtering, time gating, spatial filtering, and singular value decomposition, are investigated. These methods are applied to tomographic data of glass fiber reinforced plastic components, acquired via a <inline-formula> <tex-math notation="LaTeX">{W} </tex-math></inline-formula>-band imaging system.