Significance of a Low Noise Preamplifier and Filter Stage for Under Water Imaging Applications

High frequencies of the order of hundreds of kHz to MHz are employed for underwater imaging applications. Signal to noise ratios encountered for the front end receiver sections are seen to be very much reduced for these applications. Hence a low noise preamplifier and filter stage is very essential prior to the conventional antialiasing and digitization functionalities of the front end receivers. In this paper, an attempt is made to design and develop a low noise pre amplifier and filter to achieve a better SNR for the system. The pre amplifier stage designed is interfaced with hydrophones directly for gain and impedance matching purposes. The noise reduction is further achieved by means of a filter following the preamplifier stage which rejects the out of the band noise to an optimum level. Thorough study and analysis is carried out in this paper for the selection of low noise opamps, associated passive components and configuration of the preamplifier sections. Acoustic measurements are carried out for a sensor array of 150 kHz for evaluating the preamplifier and filter performance in the real scenario.