Wiring Arrangement Impact on Hydrophone Performance in a Polyurethane Tube

Acoustic impedance is an important parameter in underwater sound transmission and depends upon sound speed and density of the medium. Sonar Technology is a major application area of underwater (UW) acoustics. In towed array sonar a series of hydrophones are enclosed in a hose jacketing made of thermoplastic polyurethane (TPU). The density of TPU is tailored to match that of seawater to make it transparent for sound waves. Telemetry system wires run along hose jacketing and carry electrical power from platform to hydrophones and bring back electrical signals from hydrophone for further processing onboard. The electrical wires have much larger acoustic impedance than seawater. Telemetry wires can be wrapped around in helical shape or can run as a bunch along the jacketing. In both cases they cover some surface area of hydrophone and block the acoustic signal from reaching the hydrophone due to mismatch in acoustic impedance of wires and seawater. This results in weaker acoustic signal and reduces the probability of target detection. To determine efficacy of wrapped or bunch telemetry system two sets of experiments were conducted in isolated hydro-acoustic tank: telemetry wire wrapped around test hydrophone and telemetry wires in bunch running along test hydrophone. Hydrophone sensitivity in terms of sound pressure level was measured with respect to reference hydrophone in both static and dynamic conditions. Results show that bunch wire telemetry system has better performance in dynamic conditions. This can be attributed to lower acoustic impedance of bunch configuration.