Multi-Mode Electromagnetic Ultrasonic Lamb Wave Tomography Imaging for Variable-Depth Defects in Metal Plates

Area of Science:

• Materials Science
• Non-Destructive Testing
• Ultrasonic Testing

Background:

• Variable-depth defects in metal plates pose challenges for conventional inspection methods.
• Lamb waves (LWs) exhibit dispersion characteristics sensitive to plate thickness variations.
• Electromagnetic acoustic transducers (EMATs) enable efficient LW generation and detection.

Purpose of the Study:

• To develop and validate a multi-mode cross-hole tomography imaging (CTI) method for variable-depth defects.
• To investigate the sensitivity of A0 and S0 Lamb wave modes to thickness variations.
• To compare the proposed multi-mode CTI with traditional single-mode CTI methods.

Main Methods:

• Theoretical analysis of A0 and S0 mode LW sensitivities to thickness.
• Development of principles for cooperative A0 and S0 mode LW CTI.
• Experimental setup using EMAT arrays for multi-mode LW CTI on an aluminum plate with a variable-depth defect.

Main Results:

• The multi-mode LW CTI method accurately computed the thickness distribution, reflecting actual variations.
• Single-mode (S0 or A0) LW CTI failed to distinguish thickness variations within the defect region.
• Quantification of defect thickness variation was significantly more accurate with the multi-mode approach.

Conclusions:

• The proposed multi-mode electromagnetic ultrasonic LW CTI method successfully visualizes variable-depth defects in metal plates.
• This technique offers superior accuracy in quantifying defect depth compared to single-mode methods.
• The study demonstrates the practical viability of multi-mode LW CTI for advanced material inspection.