Synthetic aperture imaging for multilayer cylindrical object using an exterior rotating transducer

Area of Science:

• Ultrasound imaging
• Non-destructive testing
• Wave propagation modeling

Background:

• Synthetic Aperture Focusing Technique (SAFT) offers improved lateral resolution in ultrasound imaging.
• Existing SAFT methods require adaptation for imaging cylindrical objects, particularly those with multilayer structures.
• Exterior cylindrical scanning is preferred for objects like solid axles and pipes.

Purpose of the Study:

• To propose a frequency-domain algorithm for SAFT applied to exterior cylindrical scans of multilayer objects.
• To enhance lateral resolution in ultrasound imaging of small-diameter cylindrical components.
• To validate the algorithm using simulated and experimental data.

Main Methods:

• Derivation of a frequency-domain algorithm from Fourier-domain wave equation solutions in cylindrical coordinates.
• Extension of the algorithm to accommodate multilayer structures.
• Establishment of a simulation model for multilayer objects.
• Demonstration using simulated and experimental C-scan data.

Main Results:

• The proposed algorithm significantly improves lateral resolution for multilayer cylindrical objects compared to raw images.
• Attainable angular resolution per layer is comparable to single-layer cases under uniform transmission factors.
• Experimental verification confirms the algorithm's capability to enhance lateral resolution in both scanning directions.

Conclusions:

• The developed frequency-domain SAFT algorithm effectively improves lateral resolution for multilayer cylindrical objects using exterior scans.
• The method is suitable for imaging small-diameter pipes and axles, offering enhanced detail.
• This technique provides a valuable tool for non-destructive evaluation of cylindrical components.