We present an approach for the generation and use of coded signals with very wideband chip signals for underwater applications. We performed measurements using a parametric array in a large water tank. We fabricated a transducer consisting of a 3 mm thick and 75 mm-by-75 mm square-shaped PZT ceramic plate, which is matched to water media at the radiating face and terminated by a very low impedance at the back. We used the square-root amplitude modulation and complementary Golay sequences to code the driving signals centered around 855 kHz primary frequency. We employed a correlation receiver at reception. Our measurement results showed that generating coded signals with varying code and chip signal lengths at 10-80 kHz difference frequency range is possible. We measured that the normalized correlation receiver output at 40 kHz for a 2-chip coded signal with the widest bandwidth chip signal length of 2-cycles/chip is 0.94, which indicates a strong correlation and is consistent with those measured at other difference frequencies. As a result, we obtained well-defined coded signals with a chip length of 2-cycles/chip at a 10-80 kHz frequency range, although we also observed coded signals with shorter chip signals.

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