Ultrasonic characterization of materials. The case of polymers

Abstract

During ultrasound inspection by echo mode in polymeric materials, there is a modification of the acoustic parameters such velocity and attenuation of the transmitted wave. This work lies in the study of propagation properties and the attenuation of ultrasonic waves with a view to simultaneous evaluation of propagation velocities and attenuation of ultrasound in polymeric materials. We modeled the propagation of the ultrasonic wave through these materials, using Szabo's theoretical formulation. This reflects the frequency dependence of the absorption phenomenon and takes into account both natural and pure real integer frequency power factors. These measurements were made in echo mode, using ultrasonic transducers in a frequency band between 1 and 4 MHz. This allowed us to establish a law linking the absorption coefficient to the frequency and to assess the evolution of the phase velocity in the same frequency range, for the different types of materials studied. The results obtained are in line with those obtained by numerical simulation. The absorption phenomenon varies from one material to another. It is more significant towards high frequencies. It is also related to the distance travelled by the acoustic wave. For some materials such as polyamide and Plexiglas, the absorption coefficient has been determined with considerable precision. The results obtained further encourage the generalization of these ultrasonic methods for a real characterization of new materials.