Detection of Surface and Subsurface Flaws with Miniature GMR-Based Gradiometer

Area of Science:

• Materials Science
• Nondestructive Testing
• Sensor Technology

Background:

• Eddy-current (EC) testing is crucial for inspecting conductive materials.
• Detecting small, complex defects requires high-sensitivity probes for improved signal quality and spatial resolution.
• Existing EC probes may lack the necessary sensitivity and resolution for intricate defect characterization.

Purpose of the Study:

• To propose and validate a novel miniature eddy-current probe design utilizing a giant magnetoresistance (GMR) sensor.
• To enhance the sensitivity and spatial resolution of EC imaging for defect detection.
• To demonstrate the probe's effectiveness in characterizing small and complex-shaped defects.

Main Methods:

• Fabrication of a miniature GMR sensor on a silicon chip, comprising two spin-valve elements in a Wheatstone bridge configuration.
• Design of the GMR sensor to function as an axial gradiometer for enhanced defect sensitivity.
• Verification through numerical simulations and experimental testing with machined defects on metallic samples.

Main Results:

• The GMR-based EC probe achieved a spatial resolution of approximately 1 mm.
• Numerical simulations and experiments confirmed the probe's capability to clearly visualize defect geometric characteristics.
• The proposed probe demonstrated superior performance in characterizing defects compared to conventional methods.

Conclusions:

• The developed miniature GMR EC probe is feasible and effective for nondestructive inspection.
• This novel design significantly improves the characterization of small and complex-shaped defects in conductive materials.
• The GMR EC probe offers a promising advancement for high-resolution defect analysis in multilayer samples.