Using piezoelectric film and ultrasound resonance to determine the complete elastic tensor in one measurement

Abstract

The ultrasonic and elastic properties of materials is conventionally measured using quartz, lithium niobate, etc., transducers and a pulse‐echo technique with the transducer driven at resonance. Some problems include transducer ringing, transducer bonding, parallelism of sample faces, beam diffraction, and the necessity of remounting transducers in order to measure all of the elastic constants. Usually these problems can be minimized, but, with samples that are only a fraction of a millimeter in size, conventional ultrasound measurement becomes difficult, if not impossible. However, nearly all of these problems disappear if a resonance technique is used, and all of the elastic constants may be determined with a single measurement. For the broadband response and minimum loading by the transducer required for a resonance measurement in a small sample, polyvinylidene flouride (PVDF) piezoelectric film as thin as 9 μm is ideally suitable. Small active areas and leads are produced with metalization patterns on each side of the PVDF film. For resonance measurements, electrical cross talk across the small sample is processed by frequency modulating the drive and using phase sensitive detection. Samples with dimensions of only a few hundred microns may be measured with large signal‐to‐noise ratios. [Work supported by the Office of Naval Research and NSF Grant DMR 8701682.]