Gas‐filled spherical resonators: The current state of experiment and theory

Abstract

In the past decade, spherical acoustic resonators have proved to be useful tools for high‐accuracy measurements of the speed of sound in gases. Applications include thermophysical property determinations, acoustic thermometry, and the recent redetermination of the gas constant. The complex resonance frequencies of the resonator are described by a theoretical model that includes the effects of the viscous and thermal boundary layers, shell motion, imperfect spherical geometry, and other, less important, effects. The theoretical model is tested by comparing the consistency of speed‐of‐sound determinations using different modes, and by comparing the resonance half‐widths with the theoretical predictions. The current level of agreement of experiment and theory will be reviewed.