Measuring shell resonances of spherical acoustic resonators
Résumé
Coupling between gas and shell is a concern in the experiment used at LNE-CNAM to determine the Boltzmann constant kB by an acoustic method. As the walls of real resonators are not perfectly ridig, some perturbations occur in the frequency range of the acoustic resonances measured within helium gas contained in the caivity. As a contribution for a better understanding of the phenomenon, we have built an experiment to measure the shell modes of the spherical resonators in use in our laboratory. We report here a work in progress to assess these modes using a hammer blow method together with modal analysis. The study is carried out with air-filled, copper-walled, half-litre quasi-spherical resonator in the frequency range from 1 Hz to 20 kHz. Our results show that the shell modes expand into multiple resonances of similar modal shape, including the "breathing" mode. We confirm the observations reported in other works [4,6] of shell perturbations at other frequencies than the breathing frequency.
Domaines
Mécanique [physics.med-ph]
Origine : Fichiers produits par l'(les) auteur(s)
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