Analysis of the effect of radiating surface geometry on the beam pattern of underwater acoustic transducers

Piston-type underwater acoustic transducers are used individually as well as in arrays for various acoustic applications. Circular pistons, in particular, are widely used in arrays. However, the performance of an array with circular pistons is restricted due to the limited edge contact of the circular geometry, which in turn limits the radiating power of the array. In this study, the radiation characteristics of other common piston geometries that can readily overcome the edge contact limitation of the circular piston were theoretically investigated and compared with each other. The pistons considered include those with circular, square, hexagonal, and octagonal radiating surfaces. The analysis results confirmed that, for smaller pistons with an equivalent circular diameter less than a half wavelength, the effect of the radiation surface geometry is insignificant. As such, pistons of the other shapes can be used to overcome the limitation of the circular piston without deteriorating the radiation characteristics of the array, which opens up many possibilities regarding the design of underwater acoustic piston arrays. The validity of the theoretical analysis was verified through the finite element analysis and experimental measurement of the radiation pattern of a prototype Tonpilz transducer with an octagonal head mass.