A new high-frequency analysis of coatings using leaky Lamb waves

This study applies the leaky Lamb wave (LLW) technique to the quantitative characterization of coatings. A new decoupling method for the efficient inversion of the measured LLW data to determine the unknown elastic wave speeds of coatings is presented. The method is based on the effects of the elastic wave speeds in the substrate and coating on the frequency difference between adjacent modes known as the modal frequency spacing (MFS) at high frequency. LLW measurements were carried out on titanium and aluminum samples with 0.2–0.3 mm plasma-sprayed coating. The measured data were analyzed and inverted with the help of the proposed MFS method and excellent agreement between measurements and predictions of coating is observed. The LLW technique is shown to be potentially viable for real-time inspection of coating quality.