Resonant Ultrasound Spectroscopy (RUS) of a spherical sample in a pressuriz
ing gas atmosphere was investigated experimentally and theoretically. Measu
rements were made on a fused silica sphere in He, Ar, and N-2 gases up to p
ressures of 120 bar. The pressure-dependent shift in the resonant frequency
, Delta f, and the e-factor were measured for the S00, S11, and T02 modes.
A theoretical model based on acoustic radiation impedance was used to calcu
late Delta f and the radiation-resistance component, Q(r), of the Q-factor.
Agreement between theory and experiment was good for Q(r), but there were
discrepancies for Delta f. It was found that the theoretical Delta f due to
gas-loading effects associated with acoustic radiation was very small and
consistent with the observed dependence on pressure and gas species for the
T02 mode but not for the S00 and S11 modes. We conclude that the T02 mode
is the most reliable of these modes to use in measuring third-order elastic
constants by RUS. (C) 2000 Acoustical Society of America. [S0001-4966(00)0
3601-8].