P3L-4 BAW Phase Velocity Measurements by Conventional Pulse Echo Techniques with Correction for Couplant Effect

This work reports on the importance of considering the couplant between a fused silica buffer rod and the piezoelectric sample in pulse echo overlap measurements. A transmission line model is used to account for the couplant effect in the measurement of bulk acoustic wave (BAW) phase velocities. The couplant correction theory and the experimental procedure and setup are detailed in this paper. Experiments have been performed with quartz and langatate (LGT). Quartz, due to its well-known material properties, has been used to validate the experimental procedure and confirm the necessity of considering the couplant effect. On LGT, BAW phase velocities have been measured along plusmn45deg Y rotated cuts, and the X, Y, and Z crystalline axes for the extraction of the full set of elastic constants. The experiments revealed that the effect of the couplant accounts for a correction to the measured BAW phase velocities about one order of magnitude above other experimental uncertainties. Corrections for the phase velocity measurements on quartz and LGT of the order of 10^-3 have been verified, which indicate the relevance of the couplant correction in pulse echo based parameter extraction