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Terahertz

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Over the past several years, there has been a significant interest in the potential of terahertz (THz) detection for imaging of concealed weapons, explosives and chemical and biological agents. There are two major factors contributing to this interest :

By taking advantage of these unique radiation properties, THz imaging can be used for non destructive testing (NDT) purposes : Foreign Object Damage (FOD) and other defects such as delaminations, voids and heat damage can be identified in a variety of pre-cured and in-service composite structures.

Nowadays very little research is being performed using THz radiation for air transport NDT, and little is known on how typical composite material defects such as delamination, porosities and inclusions can be detected by THz waves. One research domain concentrates on this application domain by investigating within an international consortium the potential of developing a fast, high resolution, non-invasive and non-contact inspection system for assessing aeronautic composite parts during production. The developed NDT tool will be easy to integrate in industrial facilities and will fill in the performance gaps that are still present amongst the existing NDT techniques ; it will therefore be an extremely useful tool in NDT in terms of sensor fusion. Indeed, as always in the domain of NDT, this new method will not replace directly the existing NDT tools, but will deliver complementary results which can be sometimes more precise for some defects (like delamination or water ingress).

To achieve this overall goal, several underlying objectives need to be set and consequently achieved :

In the CISS department we will contribute by developing the signal processing algorithms based on the synthetic aperture principles know from radar applications.

The physical dimensions of the elementary components of numerous dielectric materials through which the THz waves are supposed to travel, correspond often to the applied wavelengths (tenths of microns to some millimeters) generated by the used THz source. This is the case for materials used in different domains of applications : cloths and powders for the detection of concealed explosives, and plastics and composite materials for NDT applications. From literature we know that working at wavelengths close to the size of elementary particles encountered during propagation, leads to an important decrease of the signal strength. This impacts directly the measured spectral information :

Given these important interactions between THz waves and materials, it is of uttermost importance to quantify in parallel with the above NDT survey, all the phenomena altering and degrading the propagated THz wave. Indeed, if the aim is to make from THz technology a reliable and performing detection and inspection tool, with a high probability of detection for a minimal probability of false alarms, there is a need for a fundamental research related to the THz diffusion during propagation of dielectric materials.

Research projects

F11/00

This study aims at modelling the behaviour of a THz wave in a strongly scattering dielectric, studying the THz wave scattering through dielectric materials inducing spectral distortions.

DOTNAC - Development and optimization of THz NDT tool on multi-layered composite aircraft structures.

Modern aircraft structures have to comply with severe requirements: they have to be light as well as safe. These requirements lead to an increased use of composite materials in the aircraft industry. However, new materials also require new techniques in order to inspect aircraft components during production in a non-destructive way.

The primary goal of the DOTNAC project is to develop a safe, contact-free, high resolution, and potentially on-site NDT tool based on terahertz (THz) waves, which will be easy to integrate in industrial facilities, and allowing the detection of surface, subsurface and in-depth defects in a variety of composite materials used in aeronautics. The developed NDT tool will fill in the performance gaps that are still present amongst the established NDT techniques and will therefore be an extremely useful tool in NDT in terms of sensor fusion.

C4/13

This study aims at studying the THz domain with applications in Non-Destructive Testing (NDT). One of the main development is the adaptation of Synthetic Aperture algorithms to THz sources in order to increase the cross-range resolution.

Publications

  1. Mathias Becquaert, Edison Cristofani, Johan Stiens, Marijke Vandewal, and Nikos Deligiannis. Compressed Sensing SAR Through-the-Wall Imaging with Side Information. In 26th URSI Benelux Forum, Brussels, Belgium, 2017. URSI.
  2. Edison Cristofani. Une nouvelle façon d'acquérir les signaux. Belgisch Militair Tijdschrift - Revue Militaire Belge Nr. 14, pages 121-127, June 2017.
  3. Edison Cristofani, Osama Mahfoudia, Mathias Becquaert, Xavier Neyt, François Horlin, Nikos Deligiannis, Johan Stiens, and Marijke Vandewal. Compressive Sensing and DVB-T-Based Passive Coherent Location. In 26th URSI Benelux Forum, Brussels, Belgium, 2017. URSI.
  4. Mathias Becquaert, Edison Cristofani, Gokarna Pandey, Marijke Vandewal, Johan Stiens, and Nikos Deligiannis. Compressed sensing mm-wave SAR for non-destructive testing applications using side information. In 2016 IEEE Radar Conference (RadarConf), number 2, pages 1-5. IEEE, May 2016.
  5. Edison Cristofani, Mathias Becquaert, Gokarna Pandey, Marijke Vandewal, Nikos Deligiannis, and Johan Stiens. Compressed Sensing And Defect-Based Dictionaries For Characteristics Extraction In Mm-Wave Non-Destructive Testing. In Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2016 41st International Conference on, Copenhagen, Denmark, 2016.
  6. Edison Cristofani, Fabian Friederich, Marijke Vandewal, and Joachim Jonuscheit. Non-destructive testing of aeronautics composite structures using UWB radars. In James D Taylor, editor, Advanced Ultrawideband Radar. High Resolution Materials, Sensor Systems, and Practical Applications, chapter 6, pages 237-270. Taylor & Francis Group, 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 CRC Press 2016, 2016.
  7. Edison Cristofani, Fabian Friederich, Sabine Wohnsiedler, Carsten Matheis, Joachim Jonuscheit, Marijke Vandewal, and René Beigang. Nondestructive testing potential evaluation of a terahertz frequency-modulated continuous-wave imager for composite materials inspection. Optical Engineering, 53(3):031211, 2014.
  8. Fabian Friederich, Edison Cristofani, Carsten Matheis, Joachim Jonuscheit, Rene Beigang, and Marijke Vandewal. Continuous wave terahertz inspection of glass fiber reinforced plastics with semi-automatic 3-D image processing for enhanced defect detection. In 2014 IEEE MTT-S International Microwave Symposium (IMS2014), pages 1-4. IEEE, June 2014.
  9. Fabian Friederich, Carsten Matheis, Joachim Jonuscheit, René Beigang, Edison Cristofani, and Marijke Vandewal. Terahertz FMCW Inspection of GFRP Composites: Comparison with Conventional NDT Techniques and Enhanced Defect Detection Capability through Semi-automatic 3-D Image Processing. In 2014 IEEE MTT-S International Microwave Symposium Digest, pages 1-4, Tampa Bay, FL, 2014.
  10. C. Matheis, S. Wohnsiedler, F. Ospald, E. Cristofani, A. Brook, J. Jonuscheit, R. Beigang, and M. Vandewal. Terahertz FMCW Inspection of GFRP Composites: Comparison with Conventional NDT Techniques and Enhanced Defect Detection Capability through. In Microwave Conference (GeMIC), 2014 German, pages 1-4, March 2014.
  11. M Becquaert, E Cristofani, and M Vandewal. On the applicability of compressive sensing on FMCW synthetic aperture radar data for sparse scene recovery. In European Microwave Week 2013, EuMW 2013 - Conference Proceedings; EuRAD 2013: 10th European Radar Conference, pages 9-12, October 2013.
  12. Anna Brook, Edison Cristofani, Mathias Becquaert, Ben Lauwens, Joachim Jonuscheit, and Marijke Vandewal. Applicability of compressive sensing on three-dimensional terahertz imagery for in-depth object defect detection and recognition using a dedicated semisupervised image processing methodology. Journal of Electronic Imaging, 22(2):21004, 2013.
  13. Edison Cristofani, Mathias Becquaert, and Marijke Vandewal. Performance of 2D Compressive Sensing on Wide-Beam Through-the-Wall Imaging. Journal of Electrical and Computer Engineering, 2013(636972):1-11, 2013.
  14. Edison Cristofani, Carsten Matheis, Sabine Wohnsiedler, Joachim Jonuscheit, Rene Beigang, and Marijke Vandewal. Capability of FMCW-THz Sensors for NDT of Aeronautics Materials. In 8th AIRTEC - Aerospace Sensors, Frankfurt/Mainz, 2013.
  15. C Matheis, S Wohnsiedler, J Jonuscheit, R Beigang, E Cristofani, A Brook, and M Vandewal. Inspektion von faserverst{ä}rkten Kunststoffen und Composite-Materialien unter Einsatz von Terahertz-Messtechniken. In DGZfP-Jahrestagung, Dresden, Germany, 2013.
  16. M. Vandewal, E. Cristofani, A. Brook, W. Vleugels, F. Ospald, R. Beigang, S. Wohnsiedler, C. Matheis, J. Jonuscheit, JP. Guillet, P. Mounaix, P. Venegas, I. Lopez, R. Martinez, and Y. Sternberg. Advanced Inspection of Aircraft Materials with THz Sensors. In 8th AIRTEC - Aerospace Sensors, Frankfurt/Mainz, 2013.
  17. M. Vandewal, E. Cristofani, A. Brook, W. Vleugels, F. Ospald, R. Beigang, S. Wohnsiedler, C. Matheis, J. Jonuscheit, JP. Guillet, B. Recur, P. Mounaix, I. Manek Honninger, P. Venegas, I. Lopez, R. Martinez, and Y. Sternberg. Structural health monitoring using a scanning THz system. In 2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), pages 1-2. IEEE, September 2013.
  18. A Brook, E Cristofani, M Vandewal, and J Jonuscheit. In-Depth Detection and Reconstruction Techniques using High-Frequency Microwaves for Non-Destructive Testing on Multi-Layered Composite Materials. In In Proc. of 12th Mediterranean Microwave Symposium (MMS 2012), Istanbul, Turkey, 2012.
  19. A. Brook, E. Cristofani, M. Vandewal, C. Matheis, and J. Jonuscheit. 3-D radar image processing methodology for non-destructive testing of aeronautics composite materials and structures. In IEEE National Radar Conference - Proceedings, pages 0806-0811, Atlanta, USA, May 2012.
  20. A Brook, E Cristofani, M Vandewal, C Matheis, and J Jonuscheit. Assessment of 3D Image Processing using FMCW THz Imagery. In 5th International Forum on Terahertz Spectroscopy and Imaging, number February, 2012.
  21. A. Brook, E. Cristofani, M. Vandewal, C. Matheis, J. Jonuscheit, and R. Beigang. A 3D THz image processing methodology for a fully integrated, semi-automatic and near real-time operational system. In Proceedings of SPIE, volume 8363, pages 83630E-83630E-12, Baltimore, USA, April 2012.
  22. Edison Cristofani and Marijke Vandewal. High-Resolution 3D SAR Imaging applied to Non-Destructive Testing of Multi-Layered Materials. In EUSAR 2012, number 2, pages 493-496, 2012.
  23. E Cristofani, M Becquaert, and M Vandewal. Ultra-Wideband , Non-Destructive Testing SAR Systems towards Compressive Sensing. In 1st International workshop on Compressed Sensing applied to Radar (CoSeRa 2012), number May, pages 14-16, Bonn, Germany, May 2012.
  24. E. Cristofani, A. Brook, M. Vandewal, C. Matheis, and J. Jonuscheit. Assessment of 3D Signal and Image Processing using FMCW THz Signals. In In Proc. of the OPTRO 2012, 5th International Symposium on Optronics in Defense and Security, Paris, France, 2012.
  25. E Cristofani, A Brook, M Vandewal, C Matheis, and J Jonuscheit. Synthetic Aperture Processing applied to FMCW THz Imagery. In 5th International Forum on Terahertz Spectroscopy and Imaging, Kaiserslautern, Germany, March 2012.
  26. Edison Cristofani, Anna Brook, and Marijke Vandewal. 3-D synthetic aperture processing on high-frequency wide-beam microwave systems. In Kenneth I. Ranney and Armin W. Doerry, editors, Proc. of SPIE Defense, Security, and Sensing Symposium 2012, pages 83610E-83610E-10, May 2012.
  27. Edison Cristofani, Marijke Vandewal, Carsten Matheis, and Joachim Jonuscheit. In-depth high-resolution SAR imaging using Omega-k applied to FMCW systems. In IEEE National Radar Conference - Proceedings, pages 0725-0730, 2012.
  28. J. Jonuscheit, C. Matheis, S. Wohnsiedler, M. Herrmann, R. Beigang, E. Cristofani, A. Brook, and M. Vandewal. Inspection of Aeronautics Multi-Layered Composite Structures using Terahertz Techniques. In 4 th International Symposium on NDT in Aerospace, Augsburg, Germany, 2012.
  29. M. Vandewal, J. Depauw, K. Rombaut, R. Beigang, J. Jonuscheit, P. Mounaix, I. Sáez de Ocáriz, R. Martínez Edo, A. Priegue, and Y. Sternberg. Development and optimization of THz NDT on aeronautics composite multilayered structures. In A. F. Mehdi Anwar, Nibir K. Dhar, Thomas W. Crowe, and Tariq Manzur, editors, Spie, volume 8363, pages 83630Y-83630Y-9, Kaiserslautern, Germany, May 2012.
  30. R Heremans, M Vandewal, and M Acheroy. Space-time versus frequency domain signal processing for 3D THz imaging. In Proceedings of IEEE Sensors conference, pages 739-744, October 2009.
  31. M Vandewal, R Heremans, and M Acheroy. Synthetic aperture signal processing for high resolution 3D image reconstruction in the THz-domain. In Proc of the 17th European Signal Processing Conference, pages 744-748, August 2009.
  32. Marijke Vandewal. Investigation of High Resolution SAR-Systems aboard UAV-Platforms using Simulated Raw Data. PhD thesis, Vrije Universiteit Brussel and Deutsches Zentrum für Luft- und Raumfahrt, 2006.