M. J. McKenna
P. S. Spoor
J. D. Maynard
Penn State Univ., University Park, PA 16802
The ultrasonic and elastic properties of materials are conventionally measured using quartz or lithium niobate transducers in a pulse-echo technique where the transducer is driven at resonance. Some problems include transducer ringing, transducer bonding, parallelism of the sample faces, beam diffraction, and the necessity of remounting transducers in order to measure all the elastic constants. Nearly all these problems disappear if a resonance technique is used, and all the elastic constants may be determined with a single measurement. For broadband response, minimum loading by the transducer required for a resonance measurement, and to gently contact a small fragile sample, polyvinylidene flouride (PVDF) piezoelectric film as thin as 9 (mu)m is ideally suitable. Small active areas and leads are produced with metalization patterns on each side of the PVDF film. For resonance measurements, electrical crosstalk across the small sample is processed by frequency modulating the drive and using phase sensitive detection. Small fragile samples such as aerogels or biological crystals with dimensions of only a few hundred microns may be measured with large signal-to-noise ratios. Recent measurements on the elastic anisotropy of a single grain Al--Cu--Li quasicrystal are two orders of magnitude more sensitive than conventional pulse-echo techniques and should help to resolve some of the questions over the structure of actual quasicrystalline materials. [Work supported by NSF Grant No. DMR-9000549 and by the Office of Naval Research.]