Signal-to-noise ratio optimization in hydrophone—pre-amplifier systems

Abstract

The decrease in signal-to-noise ratio caused by electronic noise is an important factor in the design of an acoustic receiving system. Normally, this loss is dominated by the hydrophone, cable, and proamplifier which make up the “front-end” of the system. In this paper, the signal-to-noise degradation factor (SND) for these components is defined. It is shown that the SND can be minimized by proper impedance matching of components. This can be accomplished either by use of a transformer or by the choice of a particular interconnection scheme for a multielement hydrophone. The minimum value of SND which can be achieved is determined by the product of figures of merit (FOM) of the hydrophone and preamplifier. For piezoelectric hydrophones, the FOM is a function of fundamental material parameters and the volume of the ceramic element. The amplifier FOM depends on the equivalent voltage and current noise sources of the device. Both charge amplifier and voltage amplifier configurations have been considered. The charge amplifier is found to have inherently poorer noise performance.