Ultrasonic spectroscopy of adhesively bonded multi-layered structures

Ultrasonic spectroscopy utilizes information in the frequency domain obtained due to the constructive and destructive interference of elastic waves for nondestructive evaluation of adhesively bonded structures. In resonance inspection (RI) an ultrasonic toneburst with a sweeping frequency is applied to an ultrasonic transducer and a resonance spectrum of the inspected structure is acquired. A theoretical model is developed in the paper to predict the modal shapes and resonance frequencies of the thickness mode resonances occurring in multi-layered structures. The model includes the piezoelectric transducer used for sensing the resonances. Modeling results are verified by the measurements performed using a network analyzer. The principles of narrow-band and wideband RI are explained, and an example of the solution to the spectrum classification issue in wideband test is presented.