INFLUENCE OF THE THICKNESS OF POLYTETRAFLUOROETHYLENE FILMS ON THE PARAMETERS OF ULTRASONIC PULSE TRANSMISSION

The transmission of ultrasonic pulses through thin polytetrafluoroethylene (PTFE) films held between Duralumin buffer rods is investigated. Films having a thickness smaller than the longitudinal ultrasonic wavelength are used. It is established that the transit time of an ultrasonic pulse through the investigated system depends on the state of the charge carriers in the film and varies with the thickness of the film. The carrier state is known from the published results of mechanical-emission analysis. It is-concluded that the state of carriers in traps must be taken into account in the interpretation of acoustical measurements on polymers. The influence of the thickness h of PTFE films on the parameters of ultrasonic pulse transmission is determined. A correlation is noted between the observed variations and the variations of the charge Q on the polymer films as recorded by mechanical-emission methods.