The Extended Helmholtz Resonator in Low Temperature Pas

Abstract

A possible way to realize a PA-cell for measurements at variable temperatures is to separate the sample and the microphone chamber. In order to retain large acoustic amplification of the whole arrangement small gas volumes and resonance type acoustic cells are required. In this work we have investigated experimentally and theoretically PA cells which make use of a narrow cylindrical tube to separate the microphone from the sample. This type of construction has already been applied for low and high temperature PAS by several research groups /1,2/. The present approach proceeds from a generalized treatment of the Helmholtz resonator model which takes into acount the retardation effects in the duct. Here we report on theoretical and experimental results obtained in the temperature range between 10 K and 300 K with the cell arrangement sketched in Figure 1. The low temperature cell consists of two chambers V1 ≅ V2 ≅ 700 mm3 and the connecting tube which has an inner diameter of 1,5 mm and a length 1 = 600 mm. Both chambers are supplied with an electret microphone. The whole construction is designed to fit into an optical cryostat. Room temperature measurements were mostly carried out with air.