Stephen C. Butler
W. Jack Hughes
Appl. Res. Lab., Penn State Univ., P. O. Box 30, State College, PA 16804
Sonar transducers with a radiating face smaller than one half wavelength tend to have a low radiation impedance load and consequently a narrow transmitting bandwidth. Thus, when the transducer is tested alone, the measured results yield a poor representation of its intended array performance. The objective of this research was to develop a fluid means to ``(rho)c'' load a single sonar transducer element by imposing a condition similar to its intended use in an array. A new method which accomplishes this and attains ``(rho)c'' loading utilizes a linear endfired waveguide, which forces a single transducer to behave as if it were in an array under ``(rho)c'' loading conditions. This is accomplished by an ``underwater linear horn array simulator'' which is composed of a rigid-walled cylindrical tube with slots of equal area equally spaced along the length of the tube. Acoustical circuit theory shows that 85% (rho)c loading over an octave bandwidth would be achieved. Measurements on a physical model confirm the prediction. Measured mechanical Q's of the sonar transducer without the horn is 7.5, and with horn is 5, showing that the loading effects of the horn have been achieved. [Work supported by ONR and NUWC, New London, CT.]