PVDF-Transducers for MHZ-Pulse-Echo Attemiatopm Measurements in Metals at Low Temperatures (Advantages and Limits)

Piezoelectric PVDF-foils have been tested as transducers for pulse-echo sound attenuation measurements at 10 to 200 MHz between 4 and 300 K. Their performance is compared with that of quartz transducers. Measurements of dislocation resonance absorption in high-purity copper single crystals are used to demonstrate that the thin foil PVDF transducers, in contrast to quartz transducers, cause no measurable dislocation effects due thermal expansion mismatch between sample and transducer, e.g. during cooling to low temperatures. However, measurements of the frequency dependence of attenua tion show that foil resonance and foil-X/ 4 interference effects have to be considered carefully with respect to measurements of stress amplitude, frequency and temperature dependence of attenuation.