A method for determining the acoustic properties of thin plates is described. Existing theoretical expressions are used to calculate transmission and reflection coefficients for sound waves striking the plates at arbitrary angles of incidence. Theory is substantiated by experimental data, and refined values for absorption coefficient and shear velocity are obtained by combining theory and experiment. Materials tested were Absonic-A, plexiglass, and polyethylene.

This paper presents the results of an experimental investigation of several passive sonar targets of the types used for calibration, marking, and tracking. Targets studied include spheres, spherical lenses, triplanes, icosahedrons, biconics, and some composite types designed to have specific frequency responses. It is concluded that, of the targets investigated, only the accurately made sphere and spherical lens are suitable for use as calibration standards under the condition of the target being supported by a flexible line. The various corner reflector configurations are suitable for marking, navigation, and tracking. The feasibility of designing passive targets with a specified frequency response is demonstrated.

This paper presents the results of an experimental investigation of the scattering of acoustic energy from finite circular cylinders in water. Photographs are shown of the pulses scattered in the backward direction in the plane normal to the longitudinal axis and in the plane containing the longitudinal axis of a cylinder. The echo structure exhibits characteristics dependent upon the corners of the cylinder where there is a sharp change in the slope of the projected area and discontinuities between air, brass, and water. The photographs of pulses returned from the cylinders in the plane normal to the longitudinal axes imply the existence of surface waves which travel around (the) circumferences of the cylinders. Distribution-in-angle diagrams of acoustic energy scattered in the plane perpendicular to the longitudinal axes of solid and hollow air-filled cylinders were taken for changes in cylinder length, changes in pulse length, and changes in acoustic radii. Length modes of vibration do not affect significantly the energy scattered perpendicular to the longitudinal axis. When pulses, which are long compared to the diameter of the cylinder, are used, the scattered energy distribution is dependent upon the composition and the acoustic radius of the cylinder.

This paper presents the results of an experimental investigation of the scattering of acoustic energy from finite circular cylinders in water. Solid and hollow brass cylinders were used as targets. Distribution-in-angle diagrams of acoustic energy scattered in the plane perpendicular to the longitudinal axis of the cylinders are shown for changes in finite cylinder length, changes in pulse length, and changes in frequency. Pulse photographs are presented to describe the echo structure of solid and hollow cylinders. Photographs are shown of the pulses scattered in the backward direction in the plane normal to the longitudinal axis of the cylinder and in the plane containing the longitudinal axis of the cylinder. The change in echo structure is presented as a function of pulse length and frequency. The echo structure exhibits characteristics dependent upon the sharp corners of the cylinder where there is a large change in slope and a discontinuity between brass and water. The photographs of pulses returned from the cylinders in the plane normal to the longitudinal axis describe the existence of surface waves which travel around the circumferences of the cylinders. (This work was partially supported by the Bureau of Ships.)

Equations are presented which describe an analytical model of the parametric receiving array and the calculated results are compared to experimental data. Beam patterns and signal levels achieved with an experimental parametric receiving array are presented to extend the ranges and frequencies of previous work conducted in model tanks to parameters of practical significance.