Abstract
A very sensitive microphone suitable for acoustic measurements in liquid helium is described. With the use of it both, the pressure amplitude of second sound and the amplitude of first sound radiated from the second sound transmitter (carbon layer heater) can be detected. By a special extension of the reciprocity theory the first sound pressure response of the microphone and the second sound transmitter response can be measured. The measured pressure signals of first and second sound are compared with the results of the two-fluid theory.
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This paper is a part of the thesis of doctorate: A. Hofmann „Kopplung zwischen Druck und Temperaturamplituden in Wellen zweiten Schalls im flüssigen Helium“, Mainz 1968.
Supported by the Stiftung Volkswagenwerk.
The authors whish to thank all members of our low temperature group for helpful ideas and discussions. We especially thank D. Brandt who has helped to develope the microphones.
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Hofmann, A., Keck, K. & Schubert, G.U. Coupling between pressure and temperature amplitudes in waves of second sound in liquid helium. Z. Physik 231, 177–192 (1970). https://doi.org/10.1007/BF01392509
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DOI: https://doi.org/10.1007/BF01392509