Hydrophone Sensor Having a Cardioid Directivity Pattern.
Final rept. 10 Apr 75-29 Mar 77,
NAVAL RESEARCH LAB WASHINGTON D C
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The electroacoustic analysis is presented together with actual acoustic performance of a hydrophone sensor configuration that is omnidirectional below its horizontal plane and having reduced sensitivity above this plane. This sensor is inherently omnidirectional in the horizontal plane. The sensor consists of an axially polled piezo-ceramic tube with pistons of different masses cemented to each end. This assembly is mounted with axis vertical inside an air filled tubular ceramic housing so that only the piston outside faces are exposed to the sound pressure. The equations are derived for the theoretical vertical directivity of the sensor as a function of vertical angle, piston dynamic mass ratio, piston radius, and sensor axial length parameters. A true cardioid directivity pattern with the maximum reduction in sensivitity above the horizontal plane for a given sensor length occurs only at a single frequency which can be calculated. The equations derived were verified from directivity measurements made on several hydrophone sensors. They were found to be valid for all sensor lengths evaluated, piston dynamic mass ratios up to 2.55, and piston radii up to .159 times the wavelength. Author
- Acoustic Detection and Detectors