ULTRASONIC SPECTROSCOPY IN POLYMERIC MATERIALS - APPLICATION OF THE KRAMERS-KRONIG RELATIONS

The propagation of ultrasonic plane waves through a material can be ex pressed by a transfer function related to the attenuation and the velo city dispersion. These acoustical parameters are determined from ultra sonic spectroscopy. Experiments were performed on different polymers a nd for the particular materials we have tested it was observed that am orphous materials can be considered as low-dispersive media, whereas i n semicrystalline materials the velocity dispersion cannot be neglecte d. These experimental results are compared with those deduced from the Kramers-Kronig relations. These analytical expressions, assuming the causality conditions of every physical system, are verified for differ ent materials proving the validity of our measurements. Other interest s of the Kramers-Kronig relations are also discussed. (C) 1996 America n Institute of Physics.