Effect of Thevenin Equivalent Internal Impedance on Velocity Control and Acoustic Power of Planar Broadside Arrays

Abstract

A Thevenin equivalent circuit for array elements, which has an input force in series with a radiation impedance and an internal impedance ZI, is discussed. The arrays considered are 80-element, close-packed, unshaded arrays, with many different ka and ZI. Four limitations to input voltage are discussed: velocity, transducer voltage, available power, and cavitation. Velocity-limited acoustic power is maximum for infinite |ZI| (equal velocities) and worst for RI=0 and XI between −XSELF and −2XSELF. Cavitation-limited acoustic power is maximum for ZI=0, when about 3 dB more power is obtained than with equal velocities and, with steered arrays, more than 3 dB. A velocity control factor UCF=|Z12|/|ZI+ZSELF| is presented, where Z12 is the mutual impedance between nearest-neighboring pistons. Velocity-limited acoustic power decreased as UCF increased.