Microwave Resonant Loaded Probe for Non-destructive Evaluation of Multilayer Composites

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Inspecting multilayer dielectric composite for subsurface defects and anomalies is critical in many applications. Towards this end, various near-field microwave non-destructive evaluation methods have been developed and applied successfully in the past. Among the various microwave probes used for this application, it has been demonstrated that circular aperture probes produce images of higher fidelity when compared to conventional rectangular aperture probes. Loading the circular aperture with a resonant structure has the potential of enhancing the sensitivity in the near-field. In this paper, thorough sensitivity analysis is performed for a circular aperture probe loaded with a resonant iris structure operating in the X-band frequency range. Extensive 3-D electromagnetic simulations are carried out to assess the sensitivity of the probe for disbond detection in multilayer composite structures at various standoff distances. The response of the probe is contrasted to a conventional rectangular aperture probe working at the same frequency (i.e., 10 GHz). The enhanced sensitivity of the iris-loaded probe is illustrated by considerable changes in the detected magnitude and phase for a composite structure with and without a disbond. It is shown that the circular aperture probe with resonant iris structure is at least three times more sensitive than the conventional rectangular aperture probe in terms of magnitude and phase change. Furthermore, to validate the simulation results, three multilayer composite samples and a fiberglass plate with holes are imaged using the aforementioned probes and their performance is compared. Relatively high resolution and qualitatively better images were rendered by the iris loaded aperture probe highlighting its efficacy and performance superiority when compared to its conventional counterpart. The overall dynamic range and signal to noise ratio values of the iris loaded probe images were at least two times higher than the rectangular probe for most samples.

Original languageBritish English
Article number5
JournalJournal of Nondestructive Evaluation
Issue number1
StatePublished - Mar 2022


  • Circular probe
  • Microwave imaging
  • Multilayer composites
  • Non-destructive testing
  • Radome structure
  • Resonant iris


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