Research on the Low-Cost Coating Detection Method Based on Electromagnetic Acoustic Transducer and Nonlinear Effect

This study introduces three nondestructive techniques for measuring coating thickness and bonding quality, critical in coating research. These techniques are nonlinear electromagnetic acoustic resonance (NEMAR), nonlinear electromagnetic ultrasound sweeping frequency (NEMUSF), and flip accumulation nonlinear single electromagnetic ultrasound sweeping frequency (FANSEMUSF). All use electromagnetic acoustic transducers (EMATs) to generate ultrasound waves with different amplitudes, which shift the resonance frequency of coated specimens. This shift helps determine the nonlinear coefficient
$\alpha $
, indicating coating thickness and bonding quality. These methods are noncontact, preventing damage to the coated specimen. The effectiveness of these techniques was proven on various coated specimens. NEMAR’s second harmonic echo signal enhances its usability. NEMUSF offers robust
$\alpha $
measurement without requiring sweeping and filtering equipment. FANSEMUSF’s simplicity, needing only a single excitation, makes it suitable for industrial applications. The quantification of the contributions of coating thickness and bonding quality to the nonlinear coefficient was not performed in this study, which could be a potential avenue for future research.