Study on Evaluation System of Mechanical Properties of Coating Materials using Wavelet Analysis of Surface Wave

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Lamb waves and Rayleigh-like waves are often used for ultrasonic NDE of plates or coatings. The dispersive nature of these waves causes difficulties in excitation and detection of ultrasonic waves as well as in the analysis of detected signals. In this study, a contact-type line-focused transducer made of a quarter-cylindrical PMMA wedge with a PVDF film adhered to the wedge is developed. It is shown that dispersive waves in plates or coatings are successfully excited and detected by this transducer. Two techniques utilizing the wavelet transform are employed to determine the dispersion relation of Lamb or Rayleigh-like waves from detected signals. In addition, the elastic properties of plates or coatings are estimated from the dispersion relation by applying an optimization technique.