High frequency resonant ultrasound spectroscopy to 50 MHz: Experimental developments and analytical refinement

High-frequency transducers up to 50MHz were developed for resonant ultrasound spectroscopy (RUS). The transducers were carefully designed as composites of high-Q (>100) and low-Q (<100) materials in order to be able to distinguish the resonant peaks of samples from the instrumental background. Combining the transducers with a high performance lock-in amplifier enabled us to conduct RUS of a specimen as small as ̃0.2 mm. One of the features of a lock-in amplifier is its ability to measure the phase of a resonance signal against the reference signal. We utilized this to subtract background noise and to decompose peaks that overlapped at a small frequency interval. The present experimental and analytical developments are useful for obtaining the elastic constants of high-pressure phases of minerals from sub millimeter single-crystal grains synthesized in a high-pressure apparatus.