Abstract
Solid-dielectric capacitance transducers, 25.4 cm in diameter, have been constructed and used to generate and detect pulses of sound waves in the frequency range from 4 to 200 kHz. The waves are propagated inside an aluminum tube, 25.4 cm i.d. and 4.5 m long. One of the transducers generates the sound pulses and can be moved axially along the tube; the second serves as a microphone, detecting the sound pulse and reflecting it at one end of the tube. The transducers are made by stretching metalized Mylar across a polished backing plate. Effects of diffraction, transducer nonalignment, and transverse modes within the tube are discussed. The sound absorption is obtained by the measurement of either the attenuation of the first pulse or the increase in the echo decay rate with distance. Pulse heights are measured with a multichannel pulse height analyzer and an on-line computer. The system has been used to measure sound absorption in humid air. [Work supported by NASA-Lewis Research Center.]
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