volume | PIER Journals

Abstract

In this work, a delamination model for millimeter-wave inspections of glass fiber reinforced polymer (GFRP) is proposed that replicates the scattering characteristics of a real delamination. The model can be used not only for the performance assessment of conventional non-destructive testing (NDT) approaches, but also for structural health monitoring (SHM) applications with permanently installed radar sensors in the frequency band from 57 to 65 GHz. Parametric numerical and experimental investigations were carried out for three different cases: (a) delamination represented by two GFRP plates with a defined air gap between the plates, (b) erosion protection tape above a GFRP plate separated by an air gap, and (c) erosion protection tape on top of a rigid foam that has similar dielectric properties to air. All signals have been processed using a damage indicator approach (DI). The numerical and experimental results show a high degree of similarity in the DI curve as a function of the delamination thickness. The differences between simulation and experiment are between 0 and 0.3 mm in delamination thickness. Hence, the proposed model can be used for the qualification of radar-based NDT and SHM systems for various practical applications, e.g. wind turbine blades, eliminating the need for expensive, destructive testing.

1. Saeed, Najmadeen Mohammed, "Recent advances in structural health monitoring: Techniques, applications and future directions," International Journal of Reliability and Safety, Vol. 18, No. 1, 55-85, 2024.
doi:10.1504/ijrs.2024.139199 Google Scholar

2. Hassani, Sahar, Mohsen Mousavi, and Amir H. Gandomi, "Structural health monitoring in composite structures: A comprehensive review," Sensors, Vol. 22, No. 1, 153, 2021.
doi:10.3390/s22010153 Google Scholar

3. Tang, Wenshuo, Jamie Blanche, Daniel Mitchell, Samuel Harper, and David Flynn, "Characterisation of composite materials for wind turbines using frequency modulated continuous wave sensing," Journal of Composites Science, Vol. 7, No. 2, 75, 2023.
doi:10.3390/jcs7020075 Google Scholar

4. Skolnik, M., Radar Handbook, McGraw-Hill, New York, 2008.

5. Simon, Jonas, Thomas Kurin, Jochen Moll, Oliver Bagemiel, Raphael Wedel, Stefan Krause, Fabian Lurz, Andreas Nuber, Vadim Issakov, and Viktor Krozer, "Embedded radar networks for damage detection in wind turbine blades: Validation in a full-scale fatigue test," Structural Health Monitoring, Vol. 22, No. 6, 4252-4263, 2023.
doi:10.1177/14759217231152815 Google Scholar

6. Beziuk, Grzegorz, Thomas C. Baum, Kamran Ghorbani, and Kelvin J. Nicholson, "Structurally integrated radar in an aerospace composite laminate," IEEE Transactions on Components, Packaging and Manufacturing Technology, Vol. 11, No. 11, 1835-1843, 2021.
doi:10.1109/tcpmt.2021.3118108 Google Scholar

7. Ciattaglia, Gianluca, Grazia Iadarola, Gianmarco Battista, Linda Senigagliesi, Ennio Gambi, Paolo Castellini, and Susanna Spinsante, "Displacement evaluation by mmWave FMCW radars: Method and performance metrics," IEEE Transactions on Instrumentation and Measurement, Vol. 73, 1-13, 2024.
doi:10.1109/tim.2024.3421440 Google Scholar

8. Pramudita, Aloysius Adya, Ding-Bing Lin, Azizka Ayu Dhiyani, Harfan Hian Ryanu, Tjahjo Adiprabowo, and Erfansyah Ali Yudha, "FMCW radar for noncontact bridge structure displacement estimation," IEEE Transactions on Instrumentation and Measurement, Vol. 72, 1-14, 2023.
doi:10.1109/tim.2023.3292960 Google Scholar

9. Ma, Zhanxiong, Jaemook Choi, Liu Yang, and Hoon Sohn, "Structural displacement estimation using accelerometer and FMCW millimeter wave radar," Mechanical Systems and Signal Processing, Vol. 182, 109582, 2023.
doi:10.1016/j.ymssp.2022.109582 Google Scholar

10. Keshmiry, Ayoub, Sahar Hassani, Mohsen Mousavi, and Ulrike Dackermann, "Effects of environmental and operational conditions on structural health monitoring and non-destructive testing: A systematic review," Buildings, Vol. 13, No. 4, 918, 2023.
doi:10.3390/buildings13040918 Google Scholar

11. Mahendran, Javagar, Francesca Schenkel, Birk Hattenhorst, Thomas Musch, Ilona Rolfes, Jan Barowski, and Christian Schulz, "Temperature and humidity effects on electromagnetic waves utilizing 140 GHz radar measurements," 2025 IEEE/MTT-S International Microwave Symposium --- IMS 2025, 713-716, San Francisco, CA, USA, 2025.
doi:10.1109/IMS40360.2025.11103768

12. Simon, Jonas, Jochen Moll, and Viktor Krozer, "Trend decomposition for temperature compensation in a radar-based structural health monitoring system of wind turbine blades," Sensors, Vol. 24, No. 3, 800, 2024.
doi:10.3390/s24030800 Google Scholar

13. Figueiredo, Eloi, Gyuhae Park, Charles R. Farrar, Keith Worden, and Joaquim Figueiras, "Machine learning algorithms for damage detection under operational and environmental variability," Structural Health Monitoring, Vol. 10, No. 6, 559-572, 2011.
doi:10.1177/1475921710388971 Google Scholar

14. Streser, Erik, Sercan Alipek, Manuel Rao, Jonas Simon, Jochen Moll, Peter Kraemer, and Viktor Krozer, "Radar-based damage detection in a wind turbine blade using convolutional neural networks: A proof-of-concept under fatigue loading," Sensors, Vol. 25, No. 11, 3337, 2025.
doi:10.3390/s25113337 Google Scholar

15. He, Wenchao, Wallace Wai-Lok Lai, Xin Sui, and Antonios Giannopoulos, "Delamination characterization in thin asphalt pavement structure using dispersive GPR data," Construction and Building Materials, Vol. 402, 132834, 2023.
doi:10.1016/j.conbuildmat.2023.132834 Google Scholar

16. Liu, Juanyu, Dan G. Zollinger, and Robert L. Lytton, "Detection of delamination in concrete pavements using ground-coupled ground-penetrating radar technique," Transportation Research Record: Journal of the Transportation Research Board, Vol. 2087, No. 1, 68-77, 2008.
doi:10.3141/2087-08 Google Scholar

17. Popovics, J. S., S. Ham, M. T. Ghasr, and R. Zoughi, "Comparison of synthetic aperture radar and impact-echo imaging for detecting delamination in concrete," AIP Conference Proceedings, Vol. 1581, No. 1, 866-871, Baltimore, MD, USA, 2014.
doi:10.1063/1.4864912

18. Tsivouraki, Niki, Konstantinos Tserpes, and Ioannis Sioutis, "Modelling of fatigue delamination growth and prediction of residual tensile strength of thermoplastic coupons," Materials, Vol. 17, No. 2, 362, 2024.
doi:10.3390/ma17020362 Google Scholar

19. Eun, Se-Won, Won-Ho Choi, Hong-Kyu Jang, Jae-Hwan Shin, Jin-Bong Kim, and Chun-Gon Kim, "Effect of delamination on the electromagnetic wave absorbing performance of radar absorbing structures," Composites Science and Technology, Vol. 116, 18-25, 2015.
doi:10.1016/j.compscitech.2015.04.001 Google Scholar

20. Xu, Xiaojuan, Tao Dai, Jin Luo, Jinling Zhao, Jinhao Qiu, Sile Chen, and Zhaoquan Chen, "Detectability of delamination in laminated CFRPs with diverse stacking sequences using eddy current method with TR pancake coil," NDT & E International, Vol. 136, 102814, 2023.
doi:10.1016/j.ndteint.2023.102814 Google Scholar

21. Akbar, Muhammad F., Ghassan N. Jawad, Laith R. Danoon, and Robin Sloan, "Delamination detection in glass-fibre reinforced polymer (GFRP) using microwave time domain reflectometry," 2018 15th European Radar Conference (EuRAD), 253-256, Madrid, Spain, 2018.
doi:10.23919/EuRAD.2018.8546540

22. Moll, Jochen, Jens Kathol, Claus-Peter Fritzen, Maria Moix-Bonet, Marcel Rennoch, Michael Koerdt, Axel S. Herrmann, Markus G. R. Sause, and Martin Bach, "Open guided waves: Online platform for ultrasonic guided wave measurements," Structural Health Monitoring, Vol. 18, No. 5-6, 1903-1914, 2018.
doi:10.1177/1475921718817169 Google Scholar

23. Baron, Samuel, Benoit Guiffard, and Ala Sharaiha, "Polyurethane membranes for flexible centimeter-wave patch antennas," Journal of Micromechanics and Microengineering, Vol. 24, No. 7, 075020, 2014.
doi:10.1088/0960-1317/24/7/075020 Google Scholar

24. Jankiraman, M., FMCW Radar Design, Artech House, 2018.

25. Pozar, David M., Microwave Engineering, John Wiley & Sons, 2012.

Mr. Manuel E. Rao

Dr. Jochen Moll

Dr. Maximilian Ebel

Dr. Peter Kraemer

Prof. Viktor Krozer