Omnidirectional guided wave inspection of large metallic plate structures using an EMAT array

Area of Science:

• Materials Science
• Non-Destructive Testing
• Ultrasonics

Background:

• Inspection of large metallic structures requires efficient methods for detecting defects.
• Guided waves offer a promising approach for inspecting plate-like structures over large areas.
• Electromagnetic Acoustic Transducers (EMATs) provide a non-contact method for generating and detecting ultrasonic waves.

Purpose of the Study:

• To describe the design of an EMAT array for inspecting large metallic plates using the S0 guided wave mode.
• To investigate the influence of mode selection on EMAT array element design.
• To demonstrate the device's capability for inspecting steel and aluminum plates and its sensitivity to defects.

Main Methods:

• Development of a novel EMAT array construction with overlapped coils for high element density.
• Utilization of the S0 guided wave mode for efficient inspection.
• Testing the device on steel and aluminum plates (5-10 mm thickness) and a 20 mm thick plate (S1 mode).

Main Results:

• The EMAT array can inspect areas of at least 10 m² from a single location.
• Signal-to-coherent noise ratio is typically around 30 dB, despite spurious signals from the A0 mode and S0 sidelobes.
• The device demonstrated sensitivity to artificial defects and corrosion patches.

Conclusions:

• The developed EMAT array is effective for inspecting large metallic plates using the S0 guided wave mode.
• The novel array design and mode selection enable efficient and sensitive defect detection.
• The technology shows feasibility for inspecting thicker plates with different guided wave modes.