Designing Quasi-Spherical Resonators for Acoustic Thermometry
J B. Mehl, Michael R. Moldover, J Pitre
We describe a quasi-spherical, noble-gas-filled cavity designed to determine the thermodynamic temperature of the gas from measurements of the frequencies and the half-widths of microwave and acoustic resonances in the cavity. The quasi-spherical shape retains the advantages of spherical acoustic resonators (non-degenerate, radially-symmetric acoustic modes, negligible viscous damping at the boundary) while simplifying the determination of the cavity's thermal expansion using microwave resonances. As a specific example, we consider a cavity bounded by four quadrants of a perfect sphere of radius a connected to each other by narrow cylindrical sections of thickness 2e1a and 2e2a where e1 and e2 are of order 10-3. The cylindrical sections split the degenerate microwave triplets (TM11, TE11, TM12, etc.) into three easily-resolved components with predictable orientations. Preliminary measurements show that two judiciously-located microwave probes excite and detect all three components of each microwave triplet with approximately equal amplitudes. We discuss the placement of acoustic transducers and the dimensions of ducts that admit gas from a manifold into the cavity.
acoustic resonator, acoustic thermometry, microwave resonator, speed of sound, thermometry
, Moldover, M.
and Pitre, J.
Designing Quasi-Spherical Resonators for Acoustic Thermometry, Metrologia
(Accessed June 2, 2023)