Comparison of equal-area cylindrical and circular piston transducers
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http://hdl.handle.net/11250/105336Utgivelsesdato
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This report is not to be cited without prior reference to the authorSammendrag
Design of sondes for in situ measurement of zooplankton or other scatterers
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 according to the principle
that the acoustically active areas be equal. Computations are performed with
the actual dimensions of six fabricated cylindrical transducers, whose beam
patterns have been measured by the manufacturer at a total of eleven frequencies
spanning the range 27-710 kHz. Nominal power levels assigned to the cylindrical
transducers are also used for both transducer types. Comparison of theoretically
computed beam patterns with measurement gives confidence in the radiation model,
which is used to compute the directivity index and on-axis sensitivity loss due
to curvature of the cylindrical transducers, referred 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 sampling volume. In every single case, the performance of the
equal-area circular piston is superior to that of the corresponding cylindrical
transducer. This is directly attributable to differences in directivity index
and curvature loss. Other, pragmatic considerations argue for the choice of the
circular piston transducer over the cylindrical transducer. Three problems
requiring future treatment are identified.