ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

1pEA13. Measurement of acoustic properties of materials at low frequencies in a water-filled tube.

Debra M. Kenney

Peter H. Rogers

Georgia Inst. of Technol., School of Mech. Eng., Atlanta, GA 30332

Two of the traditional methods for measuring the complex reflection coefficient of a material, the standing-wave tube method and the pulse tube method, each have shortcomings when the measurements are to be made in a water-filled tube at low frequencies. An acoustic impedance tube has been designed to overcome these shortcomings. The design uses a transient incident signal as opposed to a cw signal in order to minimize the problem of vibrations in the tube wall. It also uses a dual sensor system [D. Guicking and K. Karcher, Trans. ASME: J. Vib. Acoust. Stress Reliability Design 106, 393--396 (1984)] to separate the incident signal from the reflected signal without them being temporally separated. Active impedance control at the end of the tube opposite from the samples reduces the reflection from that end. The tube has been designed so that ambient pressure and temperature can be controlled during measurements to simulate an ocean environment. The analytic design of the tube and preliminary experimental results will be presented. [Work supported by ONR and NSF.]