Quantitative evaluation of thin PET film by an ultrasonic micro-spectrometer

The elastic constants of a thin polyethylene terephthalate (PET) film were obtained through the fitting of theory to the dip points in magnitude of reflection coefficients measured by an ultrasonic micro-spectrometer. It was found that the film was an orthotropic material, and the obtained elastic constants were consistent with those measured by tensile tests. Furthermore, the reflection coefficients calculated using these values reproduced not only dip points but also the change in magnitude of measured reflection coefficients depending on the frequency and the incident angle