Nondestructive evaluation of diamond film adhesion to the substrate of Si3N4 is treated by using an ultrasonic angle-beam technique. Model specimens with different values of adhesive strength were prepared and experimentally analysed. One of these specimens had a film which adhered strongly to the substrate, and another had a weakly adhering film. From the transmission coefficient obtained by fast Fourier transform, it was found that the maximum amplitude of the spectrum near the transducer centre frequency assumed higher values with better adhesion. This phenomenon is explained theoretically by considering the difference in transmission for the shear stress at the interface between the film and the substrate, which mirrors the difference in the state of adhesion.
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