An increasing demand and wide acceptance of composite components has been observed over the past few years due to their unique properties such as design flexibility, lower material costs, and improved productivity. Various non-destructive evaluation (NDE) techniques are required to detect the presence of important damage modes such as disbonds, voids, and delaminations in order to ensure the quality and performance of these structures \[1\]. 

Among the wide range of electromagnetic NDE techniques, microwave NDE is more commonly used in non-contact, rapid inspection of lossless and lowless dielectric materials such as glass fiber reinforced polymer composites \[2\]. Previous research by the authors have demonstrated the use of a conventional microwave time reversal (TR) imaging method for NDE applications \[3\]. Although the conventional TR method has the ability to detect multiple defects, diffraction limited resolutions limit the ability of this method in the presence of two closely spaced defects due to coupling of fields between them.

In order to tackle this, a TR based selective focusing method, known as the DORT (decomposition of the time reversal) \[4\], is utilized to steer and focus the microwave fields towards individual defects selectively, in case of multiple defects. This reduces the cross coupling between multiple defects, thus enhancing the imaging resolution \[5\]. The theory and overall approach of this method is discussed, followed by a computational study for detecting closely spaced multiple defects in a composite material. Simulation results from parametric studies investigate the feasibility and robustness of this approach as a promising NDE method for inspection of composites.

 

References

1.      R. Kline, “Nondestructive characterization of composite media”, Routledge, 2017.

2.      S. Kharkovsky and R. Zoughi, “Microwave and millimeter wave nondestructive testing and evaluation-overview and recent advances”, IEEE Instrumentation & Measurement Magazine, vol. 10, no. 2, pp. 26–38, 2007.

3.      S. Mukherjee, A. Tamburrino, M. Haq, S. Udpa and L. Udpa, “Far field microwave NDE of composite structures using time reversal mirror”, NDT & E International, 93:7-17, 2018.

4.      C. Prada and M. Fink, “Eigenmodes of the time reversal operator: A solution to selective focusing in multiple-target media”, Wave Motion, vol. 20, no. 2, pp. 151–163, 1994.

5.      Mehmet E Yavuz and Fernando L Teixeira, “Full time-domain dort for ultrawideband electromagnetic fields in dispersive, random inhomogeneous media”, IEEE Trans. Antennas Propag., 54(8), 2006.


A Time Reversal Based Selective Focusing Method for Microwave Nde of Gfrp Composites

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