COMPARISON OF EQUAL-AREA CYLINDRICAL AND CIRCULAR PISTON TRANSDUCERS

Design of sondes for in situ measurement of zooplankton or other scatt erers requires choosing among alternative transducer geometries. This contribution addresses the problem of choosing between cylindrical and circular piston transducers by comparing the performance of the two a ccording to the principle that the acoustically active areas be equal. Computations are performed with the actual dimensions of six fabricat ed cylindrical transducers, whose beam patterns have been measured by the manufacturer at a total of 11 frequencies spanning the range 27-71 0 kHz. Nominal power levels assigned to the cylindrical transducers ar e also used for both transducer types. Comparison of theoretically com puted beam patterns with measurement gives confidence in the radiation model, which is used to compute the directivity index and on-axis sen sitivity loss due to curvature of the cylindrical transducers, referre d to as the curvature loss. Under identical conditions of excitation, isotropic ambient noise, and detection threshold of 20 dB, the active sonar equation is exercised to estimate the maximum detection range of both single targets and multiple targets distributed throughout the s ampling volume. In every single case, the performance of the equal-are a circular piston is superior to that of the corresponding cylindrical transducer. This is directly attributable to differences in directivi ty index and curvature loss. Other, pragmatic considerations argue for the choice of the circular piston transducer over the cylindrical tra nsducer. Three problems requiring future treatment are identified.