ASA 127th Meeting M.I.T. 1994 June 6-10

4aEA2. Low-frequency impedance measuring device for underwater acoustic materials.

John E. Cole, III

Kyle Martini

Cambridge Acoust. Assoc., Inc., 200 Boston Ave., Ste. 2500, Medford, MA 02155

A laboratory testing device for measuring the direct and transfer impedances of acoustic materials below 1 kHz has been developed. The 3-ft-long test chamber accommodates 4-in.-diam material samples. Excitation of the sample is by means of an impedance head consisting of a piezoelectric tonpilz driver and force gage. Responses of the excitation and of the sample backing plate are sensed by accelerometers. The material can be hydrostatically pressurized up to 500 psia. A unique feature of the device is a water layer that couples the impedance head to the material sample. This layer permits materials to be tested after deformation under hydrostatic loading. Design features and performance characteristics of the testing device are described. Results of calibration tests and measurements on an air-rubber material are presented. [Work supported by the Office of Naval Research.]