Multi-mode dispersion compensation in Lamb wave time-reversal method for high damage sensitivity across frequencies

Area of Science:

• Structural Health Monitoring
• Non-Destructive Testing
• Wave Propagation

Background:

• Traditional time-reversal method (TRM) for Lamb wave-based damage detection suffers from amplitude dispersion.
• Amplitude dispersion prevents a zero damage index (DI) in undamaged structures and complicates threshold setting.
• Varying DI with excitation frequency reduces sensitivity and consistency in damage detection.

Purpose of the Study:

• To propose a novel technique to eliminate amplitude dispersion in the reconstructed signal after time-reversal.
• To enable a near-zero damage index (DI) threshold for improved damage detection.
• To enhance the sensitivity and reliability of Lamb wave-based structural health monitoring.

Main Methods:

• Developed a dispersion compensation technique by dividing the reconstructed signal's transfer function by the main mode transfer function (MTF) of a healthy path.
• Determined the MTF directly from forward response under broadband excitation, independent of sensing path length.
• Extended signal length for DI calculation to capture damage-induced extra modes, enhancing sensitivity.

Main Results:

• Successfully eliminated amplitude dispersion in the main mode of the reconstructed signal.
• Achieved a near-zero DI threshold for undamaged structures, consistent across frequencies.
• Demonstrated significant improvement in damage detection sensitivity and sizing for various damage types (notch, block-mass) both on and off the sensing path.

Conclusions:

• The proposed dispersion-compensated TRM effectively overcomes the amplitude dispersion limitation of traditional TRM.
• The method offers enhanced sensitivity and reliability for structural health monitoring applications.
• The technique's independence from sensing path length enables application in complex networks for damage localization.