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.