Detection of a glass fiber-reinforced polymer with defects by terahertz computed tomography

Abstract

Terahertz (THz) computed tomography (THz CT) exhibits the potential to provide a wealth of data, surpassing that of THz tomographic imaging in applications such as detecting embedded defects, particularly defect evolution within a glass fiber-reinforced polymer. To realize high-resolution THz CT, a systematic approach guided by wave propagation simulation was employed. First, the front wave of the THz beam was fine-tuned to realize a beam diameter of <2 mm. To mitigate the strong refractive effect and minimize Fresnel reflection loss, a refractive-index-matching material was fabricated and utilized as a rounded enclosure for samples with sharp corners. To further improve the reconstruction resolution, a flat surface enclosure was applied to collect all incident beams at the detector. To realize comparable results to those of full-angle CT, a limited-angle CT approach was implemented, and the frequency range 0.1-3 THz was used in the image reconstruction study. The experimental and simulated images were used to validate the findings, and conductive and non-conductive defects measuring 200 µm were successfully visualized. Additionally, a custom-built user interface enabled us to visualize the field spatial distribution of the THz beam with respect to frequency.

Keywords

THz computed tomography / THz imaging / THz spectroscopy / Fiber reinforced polymer / Internal defect imaging

Declaration of Competing Interest

The authors declare the following personal relationship which may be considered as competing interests: Benjamin Russell is currently employed by Hexcel Composites Limited. Other authors declare that there are no competing interests.

CRediT authorship contribution statement

Qing Yang Steve Wu: Writing - original draft, Validation, Methodology, Conceptualization. Nan Zhang: Formal analysis, Data curation. Vincent Lim: Project administration, Methodology, Investigation. Lei Zhang: Visualization, Validation, Investigation. Yu Zhong: Writing review & editing, Supervision, Software. Benjamin Russell: Supervision, Resources. Lin Ke: Writing - review & editing, Conceptualization.

Acknowledgements

We acknowledge the A*STAR Aerospace program (Grant Reference No: A1715a0072) for funding this project and providing ample support in project management. We also acknowledge Hexcel (Stamford, CT, USA) for supplying materials and technical discussions.

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