This paper describes the design and implementation of an ultrasonic non-contact air-coupled technique (UNCACT) using antisymmetric Lamb waves (ALW) for NDT assessments in novel composite sandwich plates of a car body shell. This technique is complemented with a C-Scan image implementation using guided waves. The finite element method (FEM) was developed using Comsol 6.1 for the interpretation of the several wave modes presented in the experiments, including the ALW mode. This FEM model is indispensable for the correct interpretation of the received signals and contributes to a better implementation of this technology. This is a novel contribution building upon previously reported work. Additionally, the phase velocity method (PVM) was applied for the verification of the ALW mode in the portion of the RF signal necessary for the C-Scan image.

Power ultrasonic transducers in industrial applications typically use Langevin-type transducers with PZT-4 piezoelectric rings. These piezoelectric rings are subjected to mechanical vibrations that fracture them. This paper describes a study of the radial mode frequency responses of fractures in piezoelectric ring-shaped elements. Four PZT-4 piezoelectric rings were used for this study. Ring 1 was preserved complete without alterations and the other 3 rings had slots of 1.0, 2.5 and 5.0 mm, respectively. Simulations were performed using Ansys Mechanical software, as well as the corresponding impedance measurements. A function generator, a digital oscilloscope and an analog circuit were used for the measurements. As a result, impedance plots of the simulations and of the measurements performed in a frequency range from 20 to 60 kHz are presented finding similar responses between simulations and measurements, it is observed in the graphs that the difference in the responses is evident, between rings with slots with respect to the ring without alterations. Based on the results obtained, it is concluded that it is possible to detect if a piezoelectric ring has fractured.

This paper describes the design and implementation of an ultrasonic non-contact air-coupled technique (UNCACT) using antisymmetric Lamb waves (ALW) for NDT assessment in novel composite sandwich plates of the car body shell. This technique is complemented with a C-Scan image implementation using this kind of guided waves. The finite element method using Comsol 6.1 is developed for the interpretation of the several wave modes presented in the experiments, including the ALW mode. The phase velocity method (PVM) is applied for the verification of the ALW mode in the portion of the RF signal necessary in the C-Scan image.