Defect detection and imaging using electromagnetic acoustic transducer with butterfly coil

Area of Science:

• Materials Science
• Non-Destructive Testing
• Acoustics

Background:

• Electromagnetic ultrasonic (EMU) detection enables couplant-free ultrasonic wave generation and reception.
• Suboptimal detection performance can arise from acoustic field spatial distribution and shear wave polarization.
• Efficient non-destructive testing is crucial for industrial applications.

Purpose of the Study:

• To investigate the acoustic field directivity of shear waves generated by a butterfly coil electromagnetic acoustic transducer (EMAT).
• To determine the optimal shear wave polarization for detecting through-hole defects using EMU.
• To evaluate the effectiveness of the phase shift migration (PSM) method for EMU data processing.

Main Methods:

• Transmission method to measure shear wave acoustic field directivity.
• Reflection method to detect through-hole defects and analyze shear wave polarization effects.
• Frequency domain phase shift migration (PSM) for signal processing and imaging.

Main Results:

• Shear wave acoustic pressure amplitude is maximized along the acoustic field axis, suitable for synthetic aperture focusing technique (SAFT) imaging.
• Higher echo amplitudes for through-hole defects are achieved when shear wave polarization is perpendicular to the defect axis.
• PSM processing of experimental data yielded high-resolution images with high computational speed.

Conclusions:

• EMU technology, with optimized shear wave polarization, can effectively detect defects.
• The PSM method significantly enhances image resolution and processing efficiency in EMU.
• This study provides a foundation for improved couplant-free ultrasonic non-destructive evaluation.