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Air-Coupled Ultrasound Time Reversal (ACU-TR) For Subwavelength Nondestructive Imaging.
Summary
Air-coupled ultrasound time reversal (ACU-TR) enhances nondestructive testing for composites. This method reconstructs pressure fields to improve defect detection and achieve subwavelength resolution, even at large separations.
Area of Science:
- Materials Science
- Acoustics
- Non-destructive Testing
Background:
- Air-coupled ultrasound (ACU) is a contact-free nondestructive testing (NDT) method offering high reproducibility.
- Increased sample-transducer separation in ACU degrades beam collimation and imaging resolution due to wave diffraction, particularly for thick composites.
- Existing ACU methods struggle with resolution at larger distances, limiting their application in production environments.
Purpose of the Study:
- To extend ACU reradiation principles for NDT of multilayered composites.
- To introduce a novel ACU time reversal (ACU-TR) method for significantly enhanced defect resolution.
- To compensate for diffraction phenomena and improve the minimum detectable defect size in ACU imaging.
Main Methods:
- The study extended ACU reradiation in unbounded media to NDT of multilayered composites.
- The ACU-TR method involved measuring the complete pressure distribution radiated by a large ACU source with point receivers (RXs).
- Acoustic holography was applied to quantitatively reconstruct the pressure field at arbitrary sample defect planes.
Main Results:
- The ACU-TR method significantly improved the defect resolution of ACU imaging.
- The technique compensated for diffraction, enabling subwavelength lateral resolution and improving the minimum detectable defect size.
- Complex wood-based composite samples were tested using ACU far-field measurements at a 160 mm separation, successfully detecting both surface and internal defects.
Conclusions:
- ACU-TR offers a powerful approach for NDT of composites, overcoming resolution limitations associated with increased sample-transducer separation.
- The method achieves subwavelength resolution, enabling the detection of smaller defects than previously possible with ACU.
- Future implementation with point receiver arrays could enable real-time data acquisition and evaluation for industrial applications.
