THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

426 15. Underwater AcousticsFigure 15.8. Cylindrical array and plane array of transducers.Examples of a cylindrical and a plane array are shown in Figure 15.8. Sphericalarrays have also been constructed for installation on submarines.Array GainThe improvement in the signal-to-noise ratio SNR, which results from the use ofarraying of hydrophones is measured by a parameter called array gain, which isdefined by()(S/N) arrayAG = 10 log(15.13)(S/N) single elementThe numerator of Equation (15.13) denotes the SNR at the array terminals and thedenominator represents the SNR of a single element of the array. It is assumed thatall the elements in the array are identical.Transducer ResponseThe effectiveness of a hydrophone in converting sound into an electric signalis called the response of the hydrophone. It relates the generated voltage to theacoustic pressure of the sound field. The receiving response of a hydrophone isdefined as the voltage produced across the terminals by a plane wave of unitacoustic pressure (the value before the introduction of the hydrophone into thesound field). The receiving response is usually expressed as the open-circuit responsethat is obtained when the hydrophone connects to an infinite impedance.The customary unit of the receiving response is the number of decibels relativeto 1 volt produced by an acoustic pressure of 1 μPa and it is written as decibelsre1V/μPa.